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Modeling Selenoprotein Se-Nitrosation: Synthesis of a Se-Nitrososelenocysteine with Persistent Stability
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  • Ryosuke Masuda
    Ryosuke Masuda
    Department of Chemistry, School of Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan
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  • Satoru Kuwano
    Satoru Kuwano
    Department of Chemistry, School of Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan
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  • Kei Goto*
    Kei Goto
    Department of Chemistry, School of Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan
    *Email: [email protected]
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    Orcidhttps://orcid.org/0000-0002-5422-1074
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Journal of the American Chemical Society

Cite this: J. Am. Chem. Soc. 2023, 145, 26, 14184–14189
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https://doi.org/10.1021/jacs.3c03394
Published June 2, 2023

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Abstract

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The Se-nitrosation in selenoproteins such as glutathione peroxidase and thioredoxin reductase to produce Se-nitrososelenocysteines (Sec–SeNOs) has been proposed to play crucial roles in signaling processes mediated by reactive nitrogen species and nitrosative-stress responses, although chemical evidence for the formation of Sec–SeNOs has been elusive not only in proteins but also in small-molecule systems. Herein, we report the first synthesis of a Sec–SeNO by employing a selenocysteine model system that bears a protective molecular cradle. The Sec–SeNO was characterized using 1H and 77Se nuclear magnetic resonance as well as ultraviolet/visible spectroscopy and found to have persistent stability at room temperature in solution. The reaction processes involving the Sec–SeNO provide experimental information that serves as a chemical basis for elucidating the reaction mechanisms involving the SeNO species in biological functions, as well as in selenol-catalyzed NO generation from S-nitrosothiols.

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Glutathione peroxidase (GPx) (1) and thioredoxin reductase (TrxR) (2) are selenoenzymes that play important and well-established roles in signaling processes mediated by reactive oxygen species (ROS) and oxidative-stress responses. (3,4) Since the 1990s, an increasing amount of research has indicated that GPx and TrxR are also crucial in signaling processes mediated by reactive nitrogen species (RNS) and nitrosative-stress responses. (5−8) In particular, GPx and TrxR constitute key components in cellular redox pathways involved in the metabolism of S-nitrosothiols (RSNOs) and peroxynitrite; by promoting the metabolism of RSNOs and peroxynitrite, GPx and TrxR are integrated into the mammalian nitrosative-stress response. (6c,8,9) It has also been reported that GPx and TrxR are sensitive to RNS and are inactivated by RSNOs and peroxynitrite. In the interactions between these selenoenzymes and RNS, the SeH groups of the selenocysteine (Sec) residues in their active sites are critically involved. (5b) Based on the inherent high nucleophilicity of selenols, the Se-nitrosation of Sec–SeH to produce Se-nitrososelenoycsteines (Sec–SeNOs) is expected in RNS-treated selenoproteins (Figure 1a), (6b,10) just as the oxidation of Sec–SeHs with ROS produces selenocysteine selenenic acids (Sec–SeOHs) as reactive intermediates. (11) However, in sharp contrast to the ubiquitous S-nitrosation (12) of various proteins and peptides, (13) SeNO modification has not yet been identified in any selenoproteins. Moreover, the observation of a Sec–SeNO in a small-molecule system has not been reported so far. Yet, for the identification of the Se-nitrosated forms of selenoproteins and the chemical elucidation of their roles in RNS-mediated signaling processes and nitrosative-stress responses, the development of a small-molecule model compound for a Sec–SeNO with sufficient stability is highly desirable.

Figure 1

Figure 1. Previous works on Se-nitrososelenols and conceptual illustration of this study.

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The formation of Se-nitrososelenols for nonselenocysteinyl derivatives has been experimentally demonstrated by our group and others. We have already reported the synthesis of BpqSeNO (14) and BmtSeNO (15) as stable Se-nitrososelenols with bulky aromatic substituents (Figure 1c). Moreover, du Mont and co-workers have reported the generation of (Me3Si)3CSeNO, which was suggested by IR spectroscopy at −78 °C, although it decomposed upon warming. (16) Mardyukov and co-workers have reported the spectroscopic identification of MeSeNO in an argon matrix at 10 K. (17)

The studies of these nonselenocysteinyl derivatives revealed that Se-nitrososelenols are more prone to bimolecular decomposition (Figure 1b) involving the formation of Se–Se bonds than other selenium-containing reactive species such as selenenic acids, which are notoriously labile due to facile self-condensation. (18) We found that BmtSeNO gradually decomposes to the corresponding diselenide at room temperature in solution, (15) while the selenenic acid bearing the same substituent, BmtSeOH, (19) exhibited high stability upon heating (Figure 1d). This instability of nonselenocysteinyl Se-nitrososelenols suggests that stabilizing Sec–SeNOs in small-molecule systems would be extremely difficult.

During our studies on modeling the reactive intermediates in the catalytic cycle of selenoenzymes, we have recently succeeded in the first observation of a Sec–SeOH (20,21) by employing a large molecular cradle (22) as an N-terminal protecting group (henceforth denoted as “Bpsc”; Figure 2A). To overcome the more facile bimolecular decomposition of Sec–SeNOs, we designed an expanded molecular cradle with peripheral 3,5-di-tert-butylphenyl units (henceforth denoted as “DB-Bpsc”; Figure 2B). Herein, we report the first synthesis of a Sec–SeNO, which is formed by Se-nitrosation of a selenocysteine model compound that bears the expanded molecular cradle (Figure 1e). The small-molecule Sec–SeNO, which was characterized by 1H and 77Se nuclear magnetic resonance (NMR) spectroscopy as well as ultraviolet–visible (UV–vis) spectroscopy, exhibited persistent stability at room temperature in solution. Some biologically relevant reaction processes involving Sec–SeNOs were investigated using this stable model compound.

Figure 2

Figure 2. Cradled selenocysteines that bear the Bpsc group (A) and the DB-Bpsc group (B).

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We thus synthesized Sec–SeH 4b bearing the DB-Bpsc group (23) as the starting material for Sec–SeNO 2b by reduction of selenocystine derivative 3 (24) (Scheme 1). The structure of the DB-Bpsc molecular cradle was unequivocally determined by single-crystal X-ray diffraction analysis of the corresponding selenocysteine selenenyl iodide (Sec–SeI; 5b). Sec–SeI 5b was obtained from the treatment of Sec–SeH 4b with N-iodosuccinimide (NIS). (25) The single-crystal X-ray diffraction analysis (Figure 3) showed that the size of the DB-Bpsc group of 5b is approximately 2.1 nm × 3.0 nm, which is much larger than that of Bpsc (1.7 nm × 2.3 nm; Figure S15). (22b) The increased steric bulk of the peripheral moiety of the DB-Bpsc cradle can be expected to more effectively suppress the bimolecular decomposition of selenocysteine-derived reactive species than the Bpsc cradle.

Scheme 1

Scheme 1. Synthesis of 4b and 5b
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Figure 3

Figure 3. Crystal structure of 5b (one of the two independent molecules).

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The synthesis of Sec–SeNO 2b by Se-nitrosation of Sec–SeH 4b with organic nitrites was then examined, and the use of an ethanol solution of t-BuONO (8.0 equiv) as a nitrosating agent in THF-d8 at room temperature was identified as the optimal conditions (Figure 4a). (26) After 13 h, the mixture gradually turned red and its 1H NMR monitoring indicated the formation of Sec–SeNO 2b in 98% yield (Figure 4b). In the 77Se NMR spectrum in CDCl3, 2b showed a signal at 2223 ppm (Figure 4c), which is in good agreement with those of the aryl-substituted Se-nitrososelenols (Figure 1c) that we have previously reported (Table S3). (14,15) To the best of our knowledge, this is the first experimental evidence for the formation of a selenocysteine-derived Se-nitrososelenol. In the 1H NMR spectrum (THF-d8), the methylene protons adjacent to the selenium atom of 2b were observed at 4.13 and 4.19 ppm, respectively. The downfield shifts of these methylene protons of Sec–SeNO 2b compared to those of Sec–SeH 4b (Table S2) indicate the presence of strong magnetic deshielding effects of the N=O group in 2b. The UV–vis spectrum of the reddish reaction mixture in CDCl3 containing Sec–SeNO 2b, which was generated by a reaction protocol similar to that shown in Figure 4a, exhibited an absorption maximum (λmax) at 446 nm (ε 167) (27) (Figure 4d), which is assignable to the n–π* transition (28) and consistent with the reported value for MeSeNO (λmax = 440 nm) in an argon matrix at 10 K. (17)

Figure 4

Figure 4. (a) Se-nitrosation of 4b. (b) 1H NMR spectrum (500 MHz, THF-d8) of 2b. (c) 77Se NMR spectrum (95 MHz, CDCl3) of 2b. (d) UV–vis (CDCl3) spectrum of 2b.

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We attempted to isolate 2b by the solvent removal-recrystallization sequence (Scheme 2a), but the resulting crystals contained not only 2b, but also diselenide 6b (2b:6b = 79:19). (29) However, under conditions other than concentrated solutions, Sec–SeNO 2b showed persistent stability; at a concentration of 8 mM in C6D6, no conversion from 2b to 6b was observed after 24 h at room temperature (Scheme 2b). Furthermore, 2b showed essentially no decomposition in the presence of excess D2O (Scheme S14). Although Se-nitrososelenols have been proposed to be thermally labile due to facile Se–NO homolysis, (10,15,16) these results indicate persistent stability for Sec–SeNOs, at least at physiological temperatures. This thermal stability of Sec–SeNO 2b stands in sharp contrast to the behavior of Sec–SeOH 1a, which undergoes spontaneous deselenation to the corresponding dehydroalanine (30,31) at room temperature. (20a) Due to the thermal instability of Sec–SeOHs, it has been proposed that the catalytic cycle of GPx must include a protective bypass mechanism that involves the intramolecular cyclization of the Sec–SeOH intermediates (32) to the corresponding cyclic selenenyl amides (33) to prevent inactivation by the deselenation from Sec–SeOHs. The stability of 2b suggests that such a protective mechanism to prevent thermal degradation is not necessary for Sec–SeNOs generated in proteins at physiological temperatures.

Scheme 2

Scheme 2. Investigation of the Stability of Sec–SeNO 2b
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In contrast to the stability of Sec–SeNO 2b under an inert gas atmosphere, 2b was found to be sensitive to air. When a C6D6 solution of Sec–SeNO 2b (77% purity) (34) was exposed to air for 2.5 h, 70% of 2b was converted to the corresponding dehydroalanine 7b (Scheme 2c). This reaction is reminiscent of the thermal deselenation of Sec–SeOHs to dehydroalanines. It is likely that dehydroalanine 7b was formed by initial oxidation of the selenium atom of 2b and subsequent β elimination. These results indicate that Sec–SeNOs are more susceptible to oxidation than their sulfur analogues, Cys–SNOs, which are relatively stable in air. (12,35) Under aerobic conditions, the SeNO modification of selenoproteins may lead to their degradation through oxidative deselenation.

Taniguchi et al. have shown that S-nitroso-N-acetyl-DL-penicillamine (SNAP) (35a) induces the inactivation of GPx, probably through SeNO modification of the Sec residue, and that the inhibitory effect of SNAP on GPx is reversed by dithiothreitol (DTT). (6b,c) It has also been reported that SNAP-mediated inactivation of GPx finally forms a selenenyl sulfide bridge between Sec45 and Cys91. Benhar et al. have reported that exposure of TrxR to S-nitrosocysteine leads to an increased formation of a selenenyl sulfide bridge between Sec498 and Cys497. (8a) These results can be feasibly interpreted by assuming that a reaction occurs between the SeNO group and the SH group of DTT or the Cys residue (Scheme 3a). We have already reported the similar reactivity of the nonselenocysteinyl Se-nitrososelenol Bpq-SeNO (Figure 1c) toward DTT and a thiol. (14) Therefore, we subsequently carried out model studies of the reaction processes of the SeNO-modified selenoenzymes with cysteine thiols or DTT using the stable selenocysteine-derived compound 2b. The 1H NMR monitoring of the reaction of Sec–SeNO 2b (74% purity) (34) with cysteine thiol 8 (3.0 equiv) in C6D6 at room temperature indicated the gradual conversion of 2b to Sec–SeS–Cys 9 in 97% conversion yield after 14 h (Scheme 3b). These results support the notion that the formation of the selenenyl sulfide in the interactions of GPx or TrxR with RSNOs involves the preceding SeNO modification of the catalytic Sec residue. When 2b (77% purity) (34) was treated with DTT (3.0 equiv) in the presence of (i-Pr)2NEt (6.0 equiv) in C6D6 at room temperature for 20 min, 2b was reduced to Sec–SeH 4b in quantitative conversion yield (Scheme 3c), suggesting that the SeNO modification of selenoenzymes can be easily reversed by reducing thiols.

Scheme 3

Scheme 3. Model Reactions of Sec–SeNO with Thiols
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We have previously reported that a Se-nitrososelenol undergoes intermolecular Se–Se bond formation more readily than a selenenic acid (Figure 1d). (15,19) The high propensity of a Sec–SeNO to undergo diselenide formation was demonstrated experimentally by the behavior of Bpsc-subsituted Sec–SeNO 2a, which is less bulky than DB-Bpsc-subsituted Sec–SeNO 2b. When Sec–SeH 4a (20a) was treated with an ethanol solution of t-BuONO (8.0 equiv) in THF-d8 at room temperature, the 1H NMR spectrum of the resulting solution after 22 h indicated the formation of a new compound derived from 4a, most likely Sec–SeNO 2a, albeit in a low yield of 26% (Figure 5a). The new compound showed spectral properties similar to those of DB-Bpsc-subsituted Sec–SeNO 2b in the 1H NMR and UV/vis spectra (Figures S3 and S4), which is consistent with the formation of Sec–SeNO 2a. However, the main product of this reaction was diselenide 6a (55% NMR yield), along with the unreacted 4a (19%) (Figure 5b). The bimolecular reaction of Sec–SeNO 2a to produce diselenide 6a was likely so fast that it was not fully suppressed by the Bpsc cradle, which can effectively protect Sec–SeOHs from self-condensation. The diselenide formation of Sec–SeNOs should be accompanied by the generation of NO. Given that S-nitrosothiols do not undergo disulfide formation very rapidly, not even when they do not carry bulky substituents, (12,36) these results suggest that the spontaneous generation of NO from Se-nitrososelenols is much faster than that from S-nitrosothiols. Recently, various diselenides (37,38) have been used as efficient catalysts for the generation of NO from Cys–SNOs. (39,40) However, many reports (6,38,39,41) have briefly summarized the mechanism for the NO generation by chemical equations in which selenols produced by the reduction of diselenides react with Cys–SNOs, leading to the release of two equivalents of NO (Figure 5c, top). Considering the ease of diselenide formation from Se-nitrososelenols, the detailed elementary-reaction processes of the catalytic NO generation can be rationalized in terms of an initial transnitrosation from Cys–SNOs to selenols to produce Se-nitrososelenols, (42) which then rapid form the diselenide with concomitant release of NO (Figure 5c, bottom).

Figure 5

Figure 5. (a) Se-nitrosation of 4a. (b) 1H NMR spectrum (500 MHz, THF-d8) of 2a. (c) Diselenide-catalyzed NO generation from Cys–SNO.

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In conclusion, we have presented the first synthesis of a Se-nitrososelenocysteine (Sec–SeNO) with persistent stability at room temperature by using a protective cradle with an expanded framework. The reaction processes involving this Sec–SeNO, along with those of its less bulky congener, provide important chemical information to elucidate the reaction mechanisms involving SeNO species in biological functions, as well as in the selenol-catalyzed NO generation from S-nitrosothiols.

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  • Corresponding Author
  • Authors
    • Ryosuke Masuda - Department of Chemistry, School of Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan
    • Satoru Kuwano - Department of Chemistry, School of Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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This work was partly supported by JSPS KAKENHI Grant Numbers JP19H02698 (K.G.) and JP21K18952 (K.G.), the Society of Iodine Science (S.K.), and JST SPRING Grant Number JPMJSP2106 (R.M.).

References

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    (c) Igarashi, J.; Nishida, M.; Hoshida, S.; Yamashita, N.; Kosaka, H.; Hori, M.; Kuzuya, T.; Tada, M. Inducible Nitric Oxide Synthase Augments Injury Elicited by Oxidative Stress in Rat Cardiac Myocytes. Am. J. Physiol. Cell Physiol. 1998, 274, C245– C252,  DOI: 10.1152/ajpcell.1998.274.1.C245
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  6. 6
    (a) Asahi, M.; Fujii, J.; Suzuki, K.; Seo, H. G.; Kuzuya, T.; Hori, M.; Tada, M.; Fujii, S.; Taniguchi, N. Inactivation of Glutathione Peroxidase by Nitric Oxide: Implication for Cytotoxicity. J. Biol. Chem. 1995, 270, 21035– 21039,  DOI: 10.1074/jbc.270.36.21035
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    6a
    Inactivation of glutathione peroxidase by nitric oxide. Implication for cytotoxicity
    Asahi, Michio; Fujii, Junichi; Suzuki, Keiichiro; Seo, Han Geuk; Kuzuya, Tsunehiko; Hori, Masatsugu; Tada, Michihiko; Fujii, Shigeru; Taniguchi, Naoyuki
    Journal of Biological Chemistry (1995), 270 (36), 21035-9CODEN: JBCHA3; ISSN:0021-9258. (American Society for Biochemistry and Molecular Biology)
    S-nitro-N-acetyl-DL-penicillamine (SNAP), a nitric oxide (NO) donor, inactivated bovine glutathione peroxidase (GPx) in a dose- and time-dependent manner. The IC50 of SNAP for GPx was 2 μM at 1 h of incubation and was 20% of the IC50 for another thiol enzyme, glyceraldehyde-3-phosphate dehydrogenase, in which a specific cysteine residue is known to be nitrosylated. Incubation of the inactivated GPx with 5 mM dithiothreitol within 1 h restored about 50% of activity of the start of the SNAP incubation. A longer exposure to NO donors, however, irreversibly inactivated the enzyme. The similarity of the inactivation with SNAP and reactivation with dithiothreitol of GPx to that of glyceraldehyde-3-phosphate dehydrogenase, suggested that NO released from SNAP modified a cysteine-like essential residue on GPx. When U937 cells were incubated with 100 μM SNAP for 1 h, a significant decrease in GPx activity was obsd. although the change was less dramatic than that with the purified enzyme, and intracellular peroxide levels increased as judged by flow cytometric anal. using a peroxide-sensitive dye. Other major antioxidative enzymes, copper/zinc superoxide dismutase, manganese superoxide dismutase, and catalase, were not affected by SNAP, which suggested that the increased accumulation of peroxides in SNAP-treated cells was due to inhibition of GPx activity by NO. Moreover, stimulation with lipopolysaccharide significantly decreased intracellular GPx activity in RAW 264.7 cells, and this effect was blocked by NO synthase inhibitor Nω-methyl-L-arginine. This indicated that GPx was also inactivated by endogenous NO. This mechanism may at least in part explain the cytotoxic effects of NO on cells and NO-induced apoptotic cell death.
    (b) Asahi, M.; Fujii, J.; Takao, T.; Kuzuya, T.; Hori, M.; Shimonishi, Y.; Taniguchi, N. The Oxidation of Selenocysteine Is Involved in the Inactivation of Glutathione Peroxidase by Nitric Oxide Donor. J. Biol. Chem. 1997, 272, 19152– 19157,  DOI: 10.1074/jbc.272.31.19152
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    6b
    The oxidation of selenocysteine is involved in the inactivation of glutathione peroxidase by nitric oxide donor
    Asahi, Michio; Fujii, Junichi; Takao, toshifumi; Kuzuya, Tsunehiko; Hori, Masatsugu; Shimonishi, Yasutsugu; Taniguchi, Naoyuki
    Journal of Biological Chemistry (1997), 272 (31), 19152-19157CODEN: JBCHA3; ISSN:0021-9258. (American Society for Biochemistry and Molecular Biology)
    Glutathione peroxidase (GPx) was inactivated by S-nitroso-N-acetyl-D,L-penicillamine (SNAP), a nitric oxide donor. The structural basis of the inactivation was studied. We also show that 3-morpholinosydnonimine N-ethylcarbamide, a peroxynitrite precursor, as well as synthetic peroxynitrite also inactivated bovine GPx. The degree of incorporation of a sulfhydryl reagent, n-octyldithionitrobenzoic acid, into GPx decreased after pretreatment with SNAP as evidenced by mass spectrometry. To identify the modification site of this enzyme by SNAP, both SNAP-pretreated and untreated GPxs were reacted with n-octyldithionnitrobenzoic acid and digested with lysylendopeptidase, and the resulting peptides were subjected to mass spectrometry. This technique identified a bridge between two peptides, one of which contains Sec45 at the catalytic center and Cys74, and the other contains Cys91. Although there are two possible combinations, selenocystine 45 (Sec45) and Cys91 or Cys74 and Cys91, the tertiary structure of GPx indicates that a cross-link between Sec45 and Cys91 is more feasible. This is consistent with the exptl. evidence that SNAP specifically inactivates GPx, in which Sec45 forms the catalytic center. Thus, we conclude that SNAP mainly oxidized Sec45 to form a selenenyl sulfide (Se-S) with a free thiol, leading to the inactivation of the enzyme. These data suggest that nitric oxide and its derivs. directly inactivate GPx in a specific manner via the prodn. of a selenenyl sulfide, resulting in an increase in intracellular peroxides that are responsible for cellular damage.
    (c) Fujii, J.; Taniguchi, N. Down regulation of superoxide dismutases and glutathione peroxidase by reactive oxygen and nitrogen species. Free Radical Res. 1999, 31, 301– 308,  DOI: 10.1080/10715769900300861
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    6c
    Down regulation of superoxide dismutases and glutathione peroxidase by reactive oxygen and nitrogen species
    Fujii, Junichi; Taniguchi, Naoyuki
    Free Radical Research (1999), 31 (4), 301-308CODEN: FRARER; ISSN:1071-5762. (Harwood Academic Publishers)
    A review, with 42 refs. The levels of antioxidative enzymes are regulated by gene expressions as well as by post-translational modifications. Although their functions are to scavenge reactive oxygen (ROS) and nitrogen species (RNS), they may also be targets of various oxidants. When ROS and RNS modify the functions of antioxidative enzymes, esp. glutathione peroxidase, they may induce apoptotic cell death in susceptible cells. It is conceivable, therefore, that at least a part of the apoptotic pathways mediated by ROS and RNS may be assocd. with modification of the redox regulation of cellular functions due to elevations of such substances. In this article we review recent findings about the effects of various oxidative conditions assocd. with alteration of these antioxidative enzymes and the concomitant cellular damage induced.
    (d) Koh, H. Y.; Suzuki, K.; Che, W.; Park, Y. S.; Miyamoto, Y.; Higashiyama, S.; Taniguchi, N. Inactivation of Glutathione Peroxidase by Nitric Oxide Leads to the Accumulation of H2O2 and the Induction of HB-EGF via c-Jun NH2-Terminal Kinase in Rat Aortic Smooth Muscle Cells. FASEB J. 2001, 15, 1335– 1492,  DOI: 10.1096/fj.00-0572fje
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  7. 7
    Nikitovic, D.; Holmgren, A. S-Nitrosoglutathione Is Cleaved by the Thioredoxin System with Liberation of Glutathione and Redox Regulating Nitric Oxide. J. Biol. Chem. 1996, 271, 19180– 19185,  DOI: 10.1074/jbc.271.32.19180
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    7
    S-nitrosoglutathione is cleaved by the thioredoxin system with liberation of glutathione and redox regulating nitric oxide
    Nikitovic, Dragana; Holmgren, Arne
    Journal of Biological Chemistry (1996), 271 (32), 19180-19185CODEN: JBCHA3; ISSN:0021-9258. (American Society for Biochemistry and Molecular Biology)
    In activated human neutrophils a burst of nitric oxide (NO) converts intracellular GSH to S-nitrosoglutathione (GSNO) which is subsequently cleaved to restore GSH by an unknown mechanism. We discovered that GSNO is an NADPH oxidizing substrate for human or calf thymus thioredoxin reductase (TR) with an apparent Km value of 60 μM and a Kcat of 0.6 × s-1. Addn. of human thioredoxin (Trx) stimulated the initial NADPH oxidn. rate severalfold but was accompanied by progressive inactivation of TR. Escherichia coli TR lacked activity with GSNO, but with E. coli Trx present, GSNO was reduced without inhibition of the enzyme. Chem. reduced E. coli Trx-(SH)2 was oxidized to Trx-S2 by GSNO with a rate const. of 760 M-1S-1 (7-fold faster than by GSSG) as measured by tryptophan fluorescence. Anal. of this reaction in the presence of oxymyoglobin revealed quant. formation of metmyoglobin indicative of NO. release. Anal. of GSNO redn. demonstrated that oxidn. of NADPH produced a stoichiometric amt. of free GSH. These results demonstrate a homolytic cleavage mechanism of GSNO, giving rise to GSH and NO. GSNO efficiently inhibited the protein disulfide reductase activity of the complete human or calf thymus thioredoxin systems. Our results demonstrate enzymic cleavage of GSNO by TR or Trx and suggest novel mechanisms for redox signaling.
  8. 8
    (a) Engelman, R.; Ziv, T.; Arnér, E. S. J.; Benhar, M. Inhibitory nitrosylation of mammalian thiredoxin reductase 1: Molecular characterization and evidence for its functional role in cellular nitroso-redox imbalance. Free Radic. Biol. Med. 2016, 97, 375– 385,  DOI: 10.1016/j.freeradbiomed.2016.06.032
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    8a
    Inhibitory nitrosylation of mammalian thioredoxin reductase 1: Molecular characterization and evidence for its functional role in cellular nitroso-redox imbalance
    Engelman, Rotem; Ziv, Tamar; Arner, Elias S. J.; Benhar, Moran
    Free Radical Biology & Medicine (2016), 97 (), 375-385CODEN: FRBMEH; ISSN:0891-5849. (Elsevier B.V.)
    Mammalian thioredoxin 1 (Trx1) and the selenoprotein Trx reductase 1 (TrxR1) are key cellular enzymes that function coordinately in thiol-based redox regulation and signaling. Recent studies have revealed that the Trx1/TrxR1 system has an S-nitrosothiol reductase (denitrosylase) activity through which it can regulate nitric oxide-related cellular processes. In this study we revealed that TrxR1 is itself susceptible to nitrosylation, characterized the underlying mechanism, and explored its functional significance. We found that nitrosothiol or nitric oxide donating agents rapidly and effectively inhibited the activity of recombinant or endogenous TrxR1. In particular, the NADPH-reduced TrxR1 was partially and reversibly inhibited upon exposure to low concns. (<10 μM) of S-nitrosocysteine (CysNO) and markedly and continuously inhibited at higher doses. Concurrently, TrxR1 very efficiently reduced low, but not high, levels of CysNO. Biochem. and mass spectrometric analyses indicated that its active site selenocysteine residue renders TrxR1 highly susceptible to nitrosylation-mediated inhibition, and revealed both thiol and selenol modifications at the two redox active centers of the enzyme. Studies in HeLa cancer cells demonstrated that endogenous TrxR1 is sensitive to nitrosylation-dependent inactivation and pointed to an important role for glutathione in reversing or preventing this process. Notably, depletion of cellular glutathione with L-buthionine-sulfoximine synergized with nitrosating agents in promoting sustained nitrosylation and inactivation of TrxR1, events that were accompanied by significant oxidn. of Trx1 and extensive cell death. Collectively, these findings expand our knowledge of the role and regulation of the mammalian Trx system in relation to cellular nitroso-redox imbalance. The observations raise the possibility of exploiting the nitrosylation susceptibility of TrxR1 for killing tumor cells.
    (b) Benhar, M. Roles of Mammalian Glutathione Peroxidase and Thioredoxin Reductase Enzymes in the Cellular Response to Nitrosative Stress. Free Radic. Biol. Med. 2018, 127, 160– 164,  DOI: 10.1016/j.freeradbiomed.2018.01.028
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    8b
    Roles of mammalian glutathione peroxidase and thioredoxin reductase enzymes in the cellular response to nitrosative stress
    Benhar, Moran
    Free Radical Biology & Medicine (2018), 127 (), 160-164CODEN: FRBMEH; ISSN:0891-5849. (Elsevier B.V.)
    A review. Mammalian cells employ elaborate antioxidant systems to effectively handle reactive oxygen and nitrogen species (ROS and RNS). At the heart of these systems operate two selenoprotein families consisting of glutathione peroxidase (GPx) and thioredoxin reductase (TrxR) enzymes. Although mostly studied in the context of oxidative stress, considerable evidence has amassed to indicate that these selenoenzymes also play important roles in nitrosative stress responses. GPx and TrxR, together with their redox partners, metabolize nitrosothiols and peroxynitrite, two major RNS. As such, these enzymes play active roles in the cellular defense against nitrosative stress. However, under certain conditions, these enzymes are inactivated by nitrosothiols or peroxynitrite, which may exacerbate oxidative and nitrosative stress in cells. The selenol groups in the active sites of GPx and TrxR enzymes are critically involved in these beneficial and detrimental processes. Further elucidation of the biochem. interactions between distinct RNS and GPx/TrxR will lead to a better understanding of the roles of these selenoenzymes in cellular homeostasis and disease.
  9. 9
    Dobashi, K.; Asayama, K.; Nakane, T.; Kodera, K.; Hayashibe, H.; Nakazawa, S. Induction of glutathione peroxidase in response to inactivation by nitric oxide. Free Radical Res. 2001, 35, 319– 327,  DOI: 10.1080/10715760100300851
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    9
    Induction of glutathione peroxidase in response to inactivation by nitric oxide
    Dobashi, Kazushige; Asayama, Kohtaro; Nakane, Takaya; Kodera, Koji; Hayashibe, Hidemasa; Nakazawa, Shinpei
    Free Radical Research (2001), 35 (3), 319-327CODEN: FRARER; ISSN:1071-5762. (Harwood Academic Publishers)
    To det. the effect of nitric oxide (NO) on cellular glutathione peroxidase (GPX) levels in living cells, we measured the activity, protein and mRNA of GPX in rat kidney (KNRK) cells under a high NO condition. Combined treatment of lipopolysaccharide (LPS, 1 μg/mL) and tumor necrosis factor-α (TNF-α, 50 ng/mL) synergistically enhanced (23-folds) nitrite prodn. from KNRK cells. This was suppressed by an inducible NO synthase (iNOS) inhibitor (aminoguanidine, N-nitro-L-arginine methylester hydrochloride) and arginase. INOS expression was detected by RT-PCR in the treated cells. GPX was inactivated irreversibly when the cells had been homogenized before exposure to the NO donor, S-nitroso-N-acetylpenicillamine (SNAP). In living KNRK cells, SNAP and LPS + TNF-α exerted a transient effect on the GPX activity. The treatment with SNAP (200 μM) or sodium nitroprusside (200 μM) enhanced GPX gene expression, which was blocked by a NO scavenger, 2-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-oxide. GPX mRNA was markedly increased by the treatment with LPS + TNF-α, and aminoguanidine blocked the effect. In cells metabolically labeled with 75Se, LPS + TNF-α accelerated the incorporation of radioactivity into GPX mols. by 2.1-fold. These results suggest that inactivation of GPX by NO triggers a signal for inducing GPX gene expression in KNRK cells, thereby restoring the intracellular level of this indispensable enzyme.
  10. 10
    Lai, C.-H.; Chou, P.-T. The Theoretical Comparison between Two Model NO Carriers, MeSNO and MeSeNO. J. Mol. Model. 2008, 14, 1– 9,  DOI: 10.1007/s00894-007-0246-z
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    10
    The theoretical comparison between two model NO carriers, MeSNO and MeSeNO
    Lai, Chin-Hung; Chou, Pi-Tai
    Journal of Molecular Modeling (2008), 14 (1), 1-9CODEN: JMMOFK; ISSN:0948-5023. (Springer GmbH)
    In this study, we apply a hybrid DFT functional, MPW1LYP, to make a comparison between MeSNO and MeSeNO. Due to the mesomeric effect and neg. hyperconjugation, Se-nitrososelenols seem to be more unstable than S-nitrosothiols regarding unimol. decompn. Interestingly, however, the barrier of the transnitrosation reaction of MeSeNO is larger than that of MeSNO, disregarding nucleophiles in the gas phase. Using the polarizable continuum model to consider the water solvent effect, the transnitrosation reactions of MeXNO and YMe- (X = S, Se; Y = S, Se) are found to undergo concerted reactions, in sharp contrast to the two-step reaction pathways concluded in the gas phase. Moreover, the barriers of the transnitrosation reactions of MeSNO for nucleophiles SMe- and SeMe- from the gas phase to the aq. soln. are found to be decreased, while the transnitrosation reactions of MeSeNO are essentially barrierless in aq. soln.
  11. 11
    (a) Flohé, L. Glutathione Peroxidase Brought into Focus. In Free Radicals in Biology; Pryor, A. W., Ed.; Academic Press: 1982.
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    There is no corresponding record for this reference.
    (b) Epp, O.; Ladenstein, R.; Wendel, A. The Refined Structure of the Selenoenzyme Glutathione Peroxidase at 0.2-nm Resolution. Eur. J. Biochem. 1983, 133, 51– 69,  DOI: 10.1111/j.1432-1033.1983.tb07429.x
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    11b
    The refined structure of the selenoenzyme glutathione peroxidase at 0.2-nm resolution
    Epp, Otto; Ladenstein, Rudolf; Wendel, Albrecht
    European Journal of Biochemistry (1983), 133 (1), 51-69CODEN: EJBCAI; ISSN:0014-2956.
    The crystal structure of bovine erythrocyte glutathione peroxidase (I) was refined by a combined procedure of restrained crystallog. refinement and energy minimization at 0.2 nm resoln. The structure at 0.28 nm resoln., which was detd. by multiple isomorphous replacement, served as a starting model. The refined model allowed a detailed survey of the H-bonding pattern and of the subunit contact areas in the mol. The model contained 165 solvent mols. per dimer, all taken as water mols. The mobility of the structure was derived from the individual at. temp. factors. The complete tetramer, including the active sites, appeared to be rather rigid, except for narrow loops near the N-terminal ends and some β turns exposed to solvent. The active centers of I were found in flat depressions on the mol. surface. The catalytically active selenocysteine residues could be located at the N-terminal ends of α helixes forming βαβ substructures together with 2 adjacent parallel β strands. In the vicinity of the reactive group, some arom. amino acid side-chains could be localized; esp. tryptophan-148, which could be H-bonded to selenocysteine-35 and may play a functional role during catalysis. The results of substrate and inhibitor binding studies in soln. and in the cryst. state could be interpreted by an apparent half-site reactivity of I. I appeared to react in the sense of neg. cooperativity with dimers being the functional units. Based on difference Fourier analyses of appropriate derivs., a reasonable model of glutathione binding is presented. Among the residues which could be of functional importance are arginine-40, glutamine-130, and arginine-167, presumably forming salt bridges and an H-bond to the glutathione mol. Thus, a general picture of a minimal reaction mechanism, which is in good agreement with functional and structural data, is proposed. The main reaction of the catalytic cycle presumably shuttles between the selenolate and the selenenic acid state of selenocysteine-35.
    (c) Maiorino, F. M.; Brigelius-Flohé, R.; Aumann, K. D.; Roveri, A.; Schomburg, D.; Flohé, L. Diversity of Glutathione Peroxidases. Methods Enzymol. 1995, 252, 38– 53,  DOI: 10.1016/0076-6879(95)52007-4
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    11c
    Diversity of glutathione peroxidases
    Ursini, F.; Maiorino, M.; Brigelius-Flohe, R.; Aumann, K. D.; Roveri, A.; Schomburg, D.; Flohe, L.
    Methods in Enzymology (1995), 252 (Biothiols, Part B), 38-53, 6 platesCODEN: MENZAU; ISSN:0076-6879. (Academic)
    In this chapter, the authors compile the structural knowledge on various glutathione peroxidase types to provide a basis for discussion of the possible biol. meaning of the structural diversification within this family of selenoenzymes.
    (d) Brigelius-Flohé, R.; Maiorino, M. Glutathione Peroxidases. Biochim. Biophys. Acta 2013, 1830, 3289– 3303,  DOI: 10.1016/j.bbagen.2012.11.020
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    11d
    Glutathione peroxidases
    Brigelius-Flohe, Regina; Maiorino, Matilde
    Biochimica et Biophysica Acta, General Subjects (2013), 1830 (5), 3289-3303CODEN: BBGSB3; ISSN:0304-4165. (Elsevier B.V.)
    A review. With increasing evidence that hydroperoxides are not only toxic but rather exert essential physiol. functions, hydroperoxide-removing enzymes need to be reviewed. In mammals, the peroxidases inter alia comprise the 8 glutathione peroxidases (GPx1-GPx8) so far identified. Since GPxs have recently been reviewed under various aspects, the authors here focus on novel findings considering their diverse physiol. roles exceeding an antioxidant activity. GPxs are involved in balancing H2O2 homeostasis in signaling cascades, e.g., in the insulin-signaling pathway by GPx1. GPx2 plays a dual role in carcinogenesis depending on the mode of initiation and cancer stage. GPx3 is membrane-assocd. possibly explaining a peroxidatic function despite low plasma concns. of GSH. GPx4 has novel roles in the regulation of apoptosis and, together with GPx5, in male fertility. The functions of GPx6 are still unknown, and the proposed involvement of GPx7 and GPx8 in protein folding awaits elucidation. Collectively, Se-contg. GPxs (GPx1-4 and Gpx6) as well as their non-selenium congeners (GPx5, GPx7, and GPx8) have become key players in important biol. contexts far beyond the detoxification of hydroperoxides.
  12. 12
    Perissinotti, L. L.; Turjanski, A. G.; Estrin, D. A.; Doctorovich, F. Transnitrosation of Nitrosothiols: Characterization of an Elusive Intermediate. J. Am. Chem. Soc. 2005, 127, 486– 487,  DOI: 10.1021/ja044056v
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    12
    Transnitrosation of Nitrosothiols: Characterization of an Elusive Intermediate
    Perissinotti, Laura L.; Turjanski, Adrian G.; Estrin, Dario A.; Doctorovich, Fabio
    Journal of the American Chemical Society (2005), 127 (2), 486-487CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    We report an investigation of the reaction between (S)-nitroso-L-cysteine Et ester and L-cysteine Et ester as a model of physiol. relevant transnitrosation processes. Our theor. and exptl. evidence clearly supports the existence of a nitroxyl disulfide intermediate in soln.
  13. 13

    For recent reviews, see

    (a) Hess, T. D.; Matsumoto, A.; Kim, S.-O.; Marshall, E. H.; Stamler, J. S. Protein S-nitrosylation: purview and parameters. Nat. Rev. Mol. Cell. Biol. 2005, 6, 150– 166,  DOI: 10.1038/nrm1569
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    13a
    Protein S-nitrosylation: purview and parameters
    Hess, Douglas T.; Matsumoto, Akio; Kim, Sung-Oog; Marshall, Harvey E.; Stamler, Jonathan S.
    Nature Reviews Molecular Cell Biology (2005), 6 (2), 150-166CODEN: NRMCBP; ISSN:1471-0072. (Nature Publishing Group)
    A review. Protein S-nitrosylation (thionitrosylation), the covalent attachment of a NO group to the thiol side-chain of Cys residues, has emerged as an important mechanism for dynamic, post-translational regulation of most or all main classes of protein. S-nitrosylation thereby conveys a large part of the ubiquitous influence of NO on cellular signal transduction, and provides a mechanism for redox-based physiol. regulation.
    (b) Nakamura, T.; Lipton, S. Redox modulation by S-nitrosylation contributes to protein misfolding, mitochondrial dynamics, and neuronal synaptic damage in neurodegenerative diseases. Cell Death Differ. 2011, 18, 1478– 1486,  DOI: 10.1038/cdd.2011.65
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    13b
    Redox modulation by S-nitrosylation contributes to protein misfolding, mitochondrial dynamics, and neuronal synaptic damage in neurodegenerative diseases
    Nakamura, T.; Lipton, S. A.
    Cell Death and Differentiation (2011), 18 (9), 1478-1486CODEN: CDDIEK; ISSN:1350-9047. (Nature Publishing Group)
    A review. The pathol. processes of neurodegenerative disorders such as Alzheimer's and Parkinson's diseases engender synaptic and neuronal cell damage. While mild oxidative and nitrosative (nitric oxide (NO)-related) stress mediates normal neuronal signaling, excessive accumulation of these free radicals is linked to neuronal cell injury or death. In neurons, N-methyl--aspartate (NMDA) receptor (NMDAR) activation and subsequent Ca2+ influx can induce the generation of NO via neuronal NO synthase. Emerging evidence has demonstrated that S-nitrosylation, representing covalent reaction of an NO group with a crit. protein thiol, mediates the vast majority of NO signaling. Analogous to phosphorylation and other posttranslational modifications, S-nitrosylation can regulate the biol. activity of many proteins. Here, we discuss recent studies that implicate neuropathogenic roles of S-nitrosylation in protein misfolding, mitochondrial dysfunction, synaptic injury, and eventual neuronal loss. Among a growing no. of S-nitrosylated proteins that contribute to disease pathogenesis, in this review we focus on S-nitrosylated protein-disulfide isomerase (forming SNO-PDI) and dynamin-related protein 1 (forming SNO-Drp1). Furthermore, we describe drugs, such as memantine and newer derivs. of this compd. that can prevent both hyperactivation of extrasynaptic NMDARs as well as downstream pathways that lead to nitrosative stress, synaptic damage, and neuronal loss. Cell Death and Differentiation (2011) 18, 1478-1486; doi:10.1038/cdd.2011.65; published online 20 May 2011.
  14. 14
    Shimada, K.; Goto, K.; Kawashima, T.; Takagi, N.; Choe, Y.-K.; Nagase, S. Isolation of a Se-Nitrososelenol: A New Class of Reactive Nitrogen Species Relevant to Protein Se-Nitrosation. J. Am. Chem. Soc. 2004, 126, 13238– 13239,  DOI: 10.1021/ja0457009
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    14
    Isolation of a Se-Nitrososelenol: A New Class of Reactive Nitrogen Species Relevant to Protein Se-Nitrosation
    Shimada, Keiichi; Goto, Kei; Kawashima, Takayuki; Takagi, Nozomi; Choe, Yoong-Kee; Nagase, Shigeru
    Journal of the American Chemical Society (2004), 126 (41), 13238-13239CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Nitric oxide (NO) is a messenger mol. implicated in a no. of physiol. processes. Nitrosation of selenoproteins has been suggested as playing an important role in NO-mediated cellular functions such as the inactivation of glutathione peroxidase (GPx), but no chem. information about Se-nitrosated species has been available to date. Here a stable Se-nitrososelenol (RSeNO), a new class of NO deriv., was synthesized and fully characterized by x-ray crystallog. and spectroscopic methods. This Se-nitrososelenol can be formed by direct transnitrosation from an S-nitrosothiol to a selenol, as is the case in the proposed mechanism for the NO-mediated inactivation of GPx.
  15. 15
    Shimada, K.; Goto, K.; Kawashima, T. Thermolysis and Photolysis of Stable Se-Nitrososelenols. Chem. Lett. 2005, 34, 654– 655,  DOI: 10.1246/cl.2005.654
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    15
    Thermolysis and photolysis of stable Se-nitrososelenols
    Shimada, Keiichi; Goto, Kei; Kawashima, Takayuki
    Chemistry Letters (2005), 34 (5), 654-655CODEN: CMLTAG; ISSN:0366-7022. (Chemical Society of Japan)
    The stable sterically encumbered bowl-type Se-nitrososelenols undergo thermal and photochem. decompn. affording diselenides. Thermolysis of 2,6-Ar2C6H3SeNO [1, Ar = 3,5-bis(2,6-diisopropylphenyl)phenyl] afforded diselenide [2,6-Ar2C6H3Se]2 (3), the structure of which was detd. by x-ray crystallog., while tetraselenide 2,6-Ar2C6H3Se4C6H3Ar2-2,6 (13) was obtained as the major product in photolysis of 1. Thermolysis of 4-tBu-2,6-R2C6H2SeNO (2, R = 2,6-bis(2,6-dimethylphenyl)phenylmethyl) gave diselenide [4-tBu-2,6-R2C6H2Se]2 (12).
  16. 16
    Wismach, C.; du Mont, W.-W.; Jones, P. G.; Ernst, L.; Papke, U.; Mugesh, G.; Kaim, W.; Wanner, M.; Becker, K. D. Selenol Nitrosation and Se-Nitrososelenol Homolysis: A Reaction Path with Possible Biochemical Implications. Angew. Chem., Int. Ed. 2004, 43, 3970– 3974,  DOI: 10.1002/anie.200453872
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    16
    Selenol nitrosation and Se-nitrososelenol homolysis: A reaction path with possible biochemical implications
    Wismach, Cathleen; du Mont, Wolf-Walther; Jones, Peter G.; Ernst, Ludger; Papke, Ulrich; Mugesh, Govindasamy; Kaim, Wolfgang; Wanner, Matthias; Becker, Klaus D.
    Angewandte Chemie, International Edition (2004), 43 (30), 3970-3974CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The nitrosation of selenols REH [E = Se, R = 2-(4,4-dimethyl-2-oxazolinyl)phenyl, (Me3Si)3Si] with tert-Bu nitrite at -78° generated the 1st Se-nitrososelenol, REN:O (2b and 4b, resp.), which were identified by IR spectroscopy and further proven by its 1,4-addn. to 2,3-dimethyl-1,3-butadiene. Compd. 2b decomps. rapidly to give diselenide R2E2. The expts. may give insight into the interactions of selenoproteins with NO in vivo.
  17. 17
    Song, L.; Keul, F.; Mardyukov, A. Preparation and Spectroscopic Identification of Methyl-Se-Nitrososelenol. Chem. Commun. 2019, 55, 9943– 9946,  DOI: 10.1039/C9CC05065E
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    17
    Preparation and spectroscopic identification of methyl-Se-nitrososelenol
    Song, Lijuan; Keul, Felix; Mardyukov, Artur
    Chemical Communications (Cambridge, United Kingdom) (2019), 55 (67), 9943-9946CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    Herein, we report, for the first time, the prepn., matrix-isolation, and spectroscopic characterization of the Me selenyl radical and methyl-Se-nitrososelenol in combination with DFT and CASSCF/NEVPT2 computations. The latter proved to be highly photolabile, and upon irradn. with light at λ = 465 nm it leads to Me selenyl and nitric oxide radical pairs. Upon λ > 730 nm irradn. it rearranges back to methyl-Se-nitrososelenol.
  18. 18
    Reich, H. J.; Hoeger, C. A.; Willis, W.W. Organoselenium Chemistry : A Study of Intermediates in the Fragmentation of Aliphatic Ketoselenoxides. Characterization of Selenoxides, Selenenamides and Selenolseleninates by 1H-,13C- and 77Se-NMR. Tetrahedron 1985, 41, 4771– 4779,  DOI: 10.1016/S0040-4020(01)96716-X
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    18
    Organoselenium chemistry. A study of intermediates in the fragmentation of aliphatic keto selenoxides. Characterization of selenoxides, selenenamides and selenol seleninates by proton, carbon-13 and selenium-77 NMR
    Reich, Hans J.; Hoeger, Carl A.; Willis, W. W. Jr.
    Tetrahedron (1985), 41 (21), 4771-9CODEN: TETRAB; ISSN:0040-4020.
    PhCOCMe2SeSe(O)CMe2COPh(I) was detected as an intermediate in the decompn. of PhCOCMe2Se(O)R [II, R = CMe2COPh, C(CH2Ph)(COMe)2]. I, which is stable in soln. below -50°, underwent thermal decompn. and reactions with P(OMe)3 to give (PhCOCMe2)Se2 and with Me2NH to give PhCOCMe2SeNMe2 as the major product. Decompn. of I in the presence of (PhCH2)2NH results in trapping PhCOCMe2SeSeOH to give PhCOCMe2SeSeN(CH2Ph)2. I could not be prepd. by oxidn. of (PhCOCMe2)2Se2. 1,2-Diselenolane III was prepd. by oxidn. of the corresponding diselenide. Cyclopropanes IV (R = OH R1 = H, Me) were generated from IV (R = CMe2COPh, C(COMe)2CH2Ph]. IV (R = CMe2COPh, R1 = H) underwent disproportionation to IV (R = OH, R1 = H) and diselenide V (R1 = H) even when prepd. at -49°. IV (R = CMe2COPh, R1 = Me) gave a selenol seleninate, which disproportionated at -17° to V (R1 = Me) and IV (R = OH, R1 = Me).
  19. 19
    Goto, K.; Nagahama, M.; Mizushima, T.; Shimada, K.; Kawashima, T.; Okazaki, R. The First Direct Oxidative Conversion of a Selenol to a Stable Selenenic Acid: Experimental Demonstration of Three Processes Included in the Catalytic Cycle of Glutathione Peroxidase. Org. Lett. 2001, 3, 3569– 3572,  DOI: 10.1021/ol016682s
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    19
    The First Direct Oxidative Conversion of a Selenol to a Stable Selenenic Acid: Experimental Demonstration of Three Processes Included in the Catalytic Cycle of Glutathione Peroxidase
    Goto, Kei; Nagahama, Michiko; Mizushima, Tadashi; Shimada, Keiichi; Kawashima, Takayuki; Okazaki, Renji
    Organic Letters (2001), 3 (22), 3569-3572CODEN: ORLEF7; ISSN:1523-7060. (American Chemical Society)
    A stable selenenic acid, I (Z = SeOH: BmtSeOH), was synthesized by direct oxidn. of selenol, BmtSeH, bearing a novel bowl-type substituent with H2O2, and its structure was established by x-ray crystallog. anal. Selenenyl sulfides obtained by the reaction of the selenenic acid with 1,4-dithiols were reduced to the corresponding selenol by treatment with a tertiary amine, thus achieving the exptl. demonstration of three processes included in the catalytic cycle of glutathione peroxidase.
  20. 20
    (a) Masuda, R.; Kimura, R.; Karasaki, T.; Sase, S.; Goto, K. Modeling the Catalytic Cycle of Glutathione Peroxidase by Nuclear Magnetic Resonance Spectroscopic Analysis of Selenocysteine Selenenic Acids. J. Am. Chem. Soc. 2021, 143, 6345– 6350,  DOI: 10.1021/jacs.1c02383
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    20a
    Modeling the catalytic cycle of glutathione peroxidase by nuclear magnetic resonance spectroscopic analysis of selenocysteine selenenic acids
    Masuda, Ryosuke; Kimura, Ryutaro; Karasaki, Takafumi; Sase, Shohei; Goto, Kei
    Journal of the American Chemical Society (2021), 143 (17), 6345-6350CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Although selenocysteine selenenic acids (Sec-SeOHs) have been recognized as key intermediates in the catalytic cycle of glutathione peroxidase (GPx), examples of the direct observation of Sec-SeOH in either protein or small-mol. systems have remained elusive so far, mostly due to their instability. Here, we report the first direct spectroscopic (1H and 77Se NMR) evidence for the formation of Sec-SeOH in small-mol. selenocysteine and selenopeptide model systems with a cradle-type protective group. The catalytic cycle of GPx was investigated using NMR-observable Sec-SeOH models. All the hitherto proposed chem. processes, i.e., not only those of the canonical catalytic cycle but also those involved in the bypass mechanism, including the intramol. cyclization of Sec-SeOH to the corresponding five-membered ring selenenyl amide, were examd. in a stepwise manner.
    (b) Masuda, R.; Goto, K. Modeling of selenocysteine-derived reactive intermediates utilizing a nano-sized molecular cavity as a protective cradle. Methods Enzymol. 2022, 662, 331– 361,  DOI: 10.1016/bs.mie.2021.10.018
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    20b
    Modeling of selenocysteine-derived reactive intermediates utilizing a nano-sized molecular cavity as a protective cradle
    Masuda, Ryosuke; Goto, Kei
    Methods in Enzymology (2022), 662 (Selenoprotein Structure and Function), 331-361CODEN: MENZAU; ISSN:1557-7988. (Elsevier Inc.)
    In the biol. functions of selenoproteins, various highly reactive species formed by oxidative modification of selenocysteine residues have been postulated to play crucial roles. Representative examples of such species are selenocysteine selenenic acids (Sec-SeOHs) and selenocysteine selenenyl iodides (Sec-SeIs), which have been widely recognized as important intermediates in the catalytic cycle of glutathione peroxidase (GPx) and iodothyronine deiodinase, resp. However, examples of even spectroscopic observation of Sec-SeOHs and Sec-SeIs in either protein or small-mol. model systems remain elusive so far, most likely due to their notorious instability. For the synthesis of small-mol. model compds. of these reactive species, it is essential to suppress their very facile bimol. decompn. such as self-condensation and disproportionation. Here we outline a novel method for the synthesis of stable small-mol. model compds. of the selenocysteine-derived reactive species, in which a nano-sized mol. cavity is used as a protective cradle to accommodate the reactive selenocysteine unit. Stabilization by the mol. cradle led to the successful synthesis of Sec-SeOHs, which are stable in soln. at low temps., and a Sec-SeI, which can be isolated as crystals. The catalytic cycle of GPx was investigated using the NMR-observable Sec-SeOH models, and all the chem. processes proposed for the catalytic cycle of GPx, including the bypass process from Sec-SeOH to the corresponding cyclic selenenyl amide, were exptl. confirmed. Detailed protocols for the syntheses of selenopeptide derivs. bearing the mol. cradle and for the spectroscopic monitoring of their reactions are provided.
  21. 21
    Masuda, R.; Kuwano, S.; Sase, S.; Bortoli, M.; Madabeni, A.; Orian, L.; Goto, K. Model Study on the Catalytic Cycle of Glutathione Peroxidase Utilizing Selenocysteine-Containing Tripeptides: Elucidation of the Protective Bypass Mechanism Involving Selenocysteine Selenenic Acids. Bull. Chem. Soc. Jpn. 2022, 95, 1360– 1379,  DOI: 10.1246/bcsj.20220156
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    21
    Model study on the catalytic cycle of glutathione peroxidase utilizing selenocysteine-containing tripeptides: Elucidation of the protective bypass mechanism involving selenocysteine selenenic acids
    Masuda, Ryosuke; Kuwano, Satoru; Sase, Shohei; Bortoli, Marco; Madabeni, Andrea; Orian, Laura; Goto, Kei
    Bulletin of the Chemical Society of Japan (2022), 95 (9), 1360-1379CODEN: BCSJA8; ISSN:0009-2673. (Chemical Society of Japan)
    Although much attention has been paid to chem. elucidation of the catalytic cycle of glutathione peroxidase (GPx), it has been hampered by instability of selenocysteine selenenic acid (Sec-SeOH) intermediates. In this study, not only chem. processes of the canonical catalytic cycle but also those involved in the bypass mechanism, including the intramol. cyclization of a Sec-SeOH to the corresponding five-membered ring selenenyl amide were demonstrated exptl. by utilizing selenopeptide model systems in which reactive intermediates can be stabilized by a nano-sized mol. cradle. The resulting cyclic selenenyl amide exhibited higher durability under oxidative conditions than in the state of a Sec-SeOH, corroborating its role as the protective form of GPx. The cyclization of Sec-SeOHs of the Sec-Gly-Thr and Sec-Gly-Lys models, which mimic the catalytic site of isoenzymes GPx1 and GPx4, resp., was found to proceed at lower temp. than in the Sec-Gly-Gly model, which corresponds to the generalized form of the tripeptides in the catalytic site of GPx. The role of the hydrogen-bond accepting moieties in the cyclization process was elucidated by DFT calcn. It was indicated that, if the selenocysteine centers are incorporated in appropriate microenvironments, the bypass mechanism can function efficiently.
  22. 22
    (a) Sase, S.; Kimura, R.; Masuda, R.; Goto, K. Model Study on Trapping of Protein Selenenic Acids by Utilizing a Stable Synthetic Congener. New J. Chem. 2019, 43, 6830– 6833,  DOI: 10.1039/C9NJ01072F
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    22a
    Model study on trapping of protein selenenic acids by utilizing a stable synthetic congener
    Sase, Shohei; Kimura, Ryutaro; Masuda, Ryosuke; Goto, Kei
    New Journal of Chemistry (2019), 43 (18), 6830-6833CODEN: NJCHE5; ISSN:1144-0546. (Royal Society of Chemistry)
    A stable primary-alkyl-substituted selenenic acid was developed as a synthetic model of selenocysteine-derived selenenic acid (Sec-SeOH) by taking advantage of a huge cavity-shaped substituent. The primary-alkyl model compd. was successfully applied to model studies on the trapping reaction of protein Sec-SeOH generated in the active site of selenoenzymes with several reagents.
    (b) Sano, T.; Masuda, R.; Sase, S.; Goto, K. Isolable Small-Molecule Cysteine Sulfenic Acid. Chem. Commun. 2021, 57, 2479– 2482,  DOI: 10.1039/D0CC08422K
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    22b
    Isolable small-molecule cysteine sulfenic acid
    Sano, Tsukasa; Masuda, Ryosuke; Sase, Shohei; Goto, Kei
    Chemical Communications (Cambridge, United Kingdom) (2021), 57 (20), 2479-2482CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
    An isolable small-mol. cysteine sulfenic acid (Cys-SOH) protected by a mol. cradle was synthesized by direct oxidn. of the corresponding cysteine thiol and its structure was established by X-ray crystallog. anal. Studies on biol. relevant reactivity indicated its usefulness as a biorepresentative small-mol. sulfenic acid model.
  23. 23
    Masuda, R.; Kuwano, S.; Goto, K. Late-Stage Functionalization of the Periphery of Oligophenylene Dendrimers with Various Arene Units via Fourfold C–H Borylation. J. Org. Chem. 2021, 86, 14433– 14443,  DOI: 10.1021/acs.joc.1c01252
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    23
    Late-Stage Functionalization of the Periphery of Oligophenylene Dendrimers with Various Arene Units via Fourfold C-H Borylation
    Masuda, Ryosuke; Kuwano, Satoru; Goto, Kei
    Journal of Organic Chemistry (2021), 86 (21), 14433-14443CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
    Late-stage functionalization of the periphery of oligophenylene dendrimers was efficiently achieved via site-selective C-H activation of a preconstructed, readily accessible dendron. By fourfold iridium-catalyzed C-H borylation followed by Suzuki-Miyaura cross-coupling, various arene units were introduced into the end points of the 1,3,5-phenylene-based hydrocarbon dendron. Coupling of the modified dendrons with a core unit, such as 2,6-dibromobenzoic acid derivs., afforded the periphery-functionalized dendrimers that also have an endohedral functionality at the core position.
  24. 24
    Selenocystine 3 was synthesized by the condensation of the acid chloride of DB-Bpsc-OH (ref ) with a selenocystine derivative (Scheme S3), which was prepared according to the following report:Stocking, E. M.; Schwarz, J. N.; Senn, H.; Salzmann, M.; Silks, L. A. Synthesis of L-Selenocystine, L-[77Se] Selenocystine and L-Tellurocystine. J. Chem. Soc., Perkin Trans. 1997, 1, 2443– 2448,  DOI: 10.1039/a600180g
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    Goto, K.; Sonoda, D.; Shimada, K.; Sase, S.; Kawashima, T. Modeling of the 5′-Deiodination of Thyroxine by Iodothyronine Deiodinase: Chemical Corroboration of a Selenenyl Iodide Intermediate. Angew. Chem., Int. Ed. 2010, 49, 545– 547,  DOI: 10.1002/anie.200905796
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    25
    Modeling of the 5'-Deiodination of Thyroxine by Iodothyronine Deiodinase: Chemical Corroboration of a Selenenyl Iodide Intermediate
    Goto, Kei; Sonoda, Daiju; Shimada, Keiichi; Sase, Shohei; Kawashima, Takayuki
    Angewandte Chemie, International Edition (2010), 49 (3), 545-547, S545/1-S545/6CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Herein, we report exptl. evidence for the formation of a selenenyl iodide in 5'-deiodination of a thyroxine deriv. by an organoselenol, through the use of a nanosized mol. cavity to stabilize the selenenyl iodide intermediate.
  26. 26

    Details of the optimization of the reaction conditions are given in the SI (Scheme S7). We have previously reported that Se-nitrosation of an aromatic selenol to a Se-nitrososelenol was sufficiently fast in CDCl3. However, in the case of Sec–SeH 2b, its Se-nitrosation was slower under similar conditions; for details, see the SI (Figure S5).

    There is no corresponding record for this reference.
  27. 27

    In addition, there was also a very weak absorption at ∼640 nm, which was assigned to the π–π* transition on the basis of our previous DFT calculations on PhSeNO (711 nm); for details, see ref (14).

    There is no corresponding record for this reference.
  28. 28

    The observed absorption maximum of Sec–SeNO 2b is in good agreement with those of our previously reported Se-nitrososelenols; for details, see the SI (Table S4).

    There is no corresponding record for this reference.
  29. 29

    Determined by 1H NMR spectroscopy; we propose that diselenide 6b was formed during the concentration of the reaction mixture containing Sec–SeNO 2b.

    There is no corresponding record for this reference.
  30. 30
    Walter, R.; Roy, J. Selenomethionine, a Potential Catalytic Antioxidant in Biological Systems. J. Org. Chem. 1971, 36, 2561– 2563,  DOI: 10.1021/jo00816a045
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    Selenomethionine, a potential catalytic antioxidant in biological systems
    Walter, Roderich; Roy, Jyotirmoy
    Journal of Organic Chemistry (1971), 36 (17), 2561-3CODEN: JOCEAH; ISSN:0022-3263.
    Z = CO2CH2Ph in this abstr. N-Carbobenzoxy-DL-selenomethionine diphenylmethyl ester (I) is treated with NaIO4 or dil. H2O2 to give the selenoxide, MeSe(O)CH2CH2CH(NHZ)CO2CHPh2, which slowly loses O to give I. N-Carbobenzoxydehydroalanine, not the resp. selenoxides, are obtained from the selenocysteine deriv. and the selenocystine deriv., Ph2CHSeCH2CH(NHZ)CO2CHPh2 and Ph2CHO2CCH(NHZ)CH2SeSeCH2(NHZ)CO2ChPh2.
  31. 31
    Ma, S.; Caprioli, R. M.; Hill, K. E.; Burk, R. F. Loss of Selenium from Selenoproteins: Conversion of Selenocysteine to Dehydroalanine in Vitro. J. Am. Soc. Mass Spectrom. 2003, 14, 593– 600,  DOI: 10.1016/S1044-0305(03)00141-7
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    31
    Loss of selenium from selenoproteins: conversion of selenocysteine to dehydroalanine in vitro
    Ma, Shuguang; Caprioli, Richard M.; Hill, Kristina E.; Burk, Raymond F.
    Journal of the American Society for Mass Spectrometry (2003), 14 (6), 593-600CODEN: JAMSEF; ISSN:1044-0305. (Elsevier Science Inc.)
    Characterization of reduced and alkylated rat selenoprotein P by mass spectrometry yielded selenopeptides from which one or more selenium atoms were missing. Predicted selenopeptide mass peaks were accompanied by peaks corresponding to the conversion of one or more selenocysteine residues to dehydroalanine(s). Expts. were carried out to det. whether this loss of selenium occurred in vitro. A selenopeptide was isolated that contained two selenocysteine residues that were both in selenide-sulfide linkages with cysteine residues. After the peptide had been reduced and alkylated, in addn. to the predicted mass peak with both selenocysteine residues present, two mass peaks were detected at positions expected for conversion of one and two selenocysteine residues of this selenopeptide to dehydroalanine residues, which was confirmed by tandem mass spectrometry. Similar findings were obtained from a study of another selenoprotein, rat plasma glutathione peroxidase. These results indicate that selenium atoms are lost from selenoproteins during purifn. and characterization. The loss of selenium from selenoproteins is probably through the mechanism of oxidn. of selenocysteine residue to selenoxide followed by syn-β-elimination of selenenic acid during sample processing.
  32. 32
    Orian, L.; Mauri, P.; Roveri, A.; Toppo, S.; Benazzi, L.; Bosello-Travain, V.; De Palma, A.; Maiorino, M.; Miotto, G.; Zaccarin, M.; Polimeno, A.; Flohé, L.; Ursini, F. Selenocysteine Oxidation in Glutathione Peroxidase Catalysis: An MS-Supported Quantum Mechanics Study. Free Radic. Biol. Med. 2015, 87, 1– 14,  DOI: 10.1016/j.freeradbiomed.2015.06.011
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    32
    Selenocysteine oxidation in glutathione peroxidase catalysis: an MS-supported quantum mechanics study
    Orian, Laura; Mauri, Pierluigi; Roveri, Antonella; Toppo, Stefano; Benazzi, Louise; Bosello-Travain, Valentina; De Palma, Antonella; Maiorino, Matilde; Miotto, Giovanni; Zaccarin, Mattia; Polimeno, Antonino; Flohe, Leopold; Ursini, Fulvio
    Free Radical Biology & Medicine (2015), 87 (), 1-14CODEN: FRBMEH; ISSN:0891-5849. (Elsevier B.V.)
    Glutathione peroxidases (GPxs) are enzymes working with either selenium or sulfur catalysis. They adopted diverse functions ranging from detoxification of H2O2 to redox signaling and differentiation. The relative stability of the selenoenzymes, however, remained enigmatic in view of the postulated involvement of a highly unstable selenenic acid form during catalysis. Nevertheless, d. functional theory calcns. obtained with a representative active site model verify the mechanistic concept of GPx catalysis and underscore its efficiency. However, they also allow that the selenenic acid, in the absence of the reducing substrate, reacts with a nitrogen in the active site. MS/MS anal. of oxidized rat GPx4 complies with the predicted structure, an 8-membered ring, in which selenium is bound as selenenylamide to the protein backbone. The intermediate can be re-integrated into the canonical GPx cycle by glutathione, whereas, under denaturing conditions, its selenium moiety undergoes β-cleavage with formation of a dehydro-alanine residue. The selenenylamide bypass prevents destruction of the redox center due to over-oxidn. of the selenium or its elimination and likely allows fine-tuning of GPx activity or alternate substrate reactions for regulatory purposes.
  33. 33
    (a) Reich, H. J.; Jasperse, C. P. Organoselenium Chemistry. Redox Chemistry of Selenocysteine Model Systems. J. Am. Chem. Soc. 1987, 109, 5549– 5551,  DOI: 10.1021/ja00252a055
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    33a
    Organoselenium chemistry. Redox chemistry of selenocysteine model systems
    Reich, Hans J.; Jasperse, Craig P.
    Journal of the American Chemical Society (1987), 109 (18), 5549-51CODEN: JACSAT; ISSN:0002-7863.
    Two model systems for the selenocysteine active site of the selenoenzyme glutathione peroxidase have been prepd., and their redox chem. was studied. The 1st is 2,2-dimethyl-3-selenopropionic acid and the 2nd is N-acetyl-N'-methyl-α-methylselenocysteamide. Selenides PhCOCMe2SeCH2CRMeCONHMe (R = Me, NHAc) were oxidized by O3 to give selenenic acids HOSeCH2CRMeCONHMe, which underwent in situ cyclization to give cyclic selenamides I [R = Me (II), NHAc]. In aq. McCN, II was in equil. with diselenide (SeCH2CMe2CONHMe)2 (III) and cyclic seleninamide IV. Such equil. are usually completely on the side of the disproportionation products. The reactions of II and IV with PhCH2SH and Me3CSH were studied. The reaction of IV with PhCH2SH gave sequentially PhCH2SSe(O)CH2CMe2CONHMe, II, PhCH2SSeCH2CMe2CONHMe, and finally HSeCH2CMe2CONHMe (V), following closely the proposed mechanism for the redn. steps in the glutathione peroxidase catalytic cycle. Oxidn. of V with either tert-Bu hydroperoxide or m-chloroperbenzoic acid gave in sequence III, II, and IV.
    (b) Sarma, B. K.; Mugesh, G. Glutathione Peroxidase (GPx)-like Antioxidant Activity of the Organoselenium Drug Ebselen: Un-expected Complications with Thiol Exchange Reactions. J. Am. Chem. Soc. 2005, 127, 11477– 11485,  DOI: 10.1021/ja052794t
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    33b
    Glutathione Peroxidase (GPx)-like Antioxidant Activity of the Organoselenium Drug Ebselen: Unexpected Complications with Thiol Exchange Reactions
    Sarma, Bani Kanta; Mugesh, G.
    Journal of the American Chemical Society (2005), 127 (32), 11477-11485CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    The factors that are responsible for the relatively low glutathione peroxidase (GPx)-like antioxidant activity of organoselenium compds. such as ebselen (1, 2-phenyl-1,2-benzisoselenazol-3(2H)-one) in the redn. of hydroperoxides with arom. thiols such as benzenethiol and 4-methylbenzenethiol as cosubstrates are described. Exptl. and theor. investigations reveal that the relatively poor GPx-like catalytic activity of organoselenium compds. is due to the undesired thiol exchange reactions that take place at the selenium center in the selenyl sulfide intermediate. This study suggests that any substituent that is capable of enhancing the nucleophilic attack of thiol at sulfur in the selenyl sulfide state would enhance the antioxidant potency of organoselenium compds. such as ebselen. It is proved that the use of thiol having an intramolecularly coordinating group would enhance the biol. activity of ebselen and other organoselenium compds. The presence of strong S···N or S···O interactions in the selenyl sulfide state can modulate the attack of an incoming nucleophile (thiol) at the sulfur atom of the -Se-S- bridge and enhance the GPx activity by reducing the barrier for the formation of the active species selenol.
    (c) Bhowmick, D.; Srivastava, S.; D’Silva, P.; Mugesh, G. Highly Efficient Glutathione Peroxidase and Peroxiredoxin Mimetics Protect Mammalian Cells against Oxidative Damage. Angew. Chem., Int. Ed. 2015, 54, 8449– 8453,  DOI: 10.1002/anie.201502430
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    33c
    Highly Efficient Glutathione Peroxidase and Peroxiredoxin Mimetics Protect Mammalian Cells against Oxidative Damage
    Bhowmick, Debasish; Srivastava, Shubhi; D'Silva, Patrick; Mugesh, Govindasamy
    Angewandte Chemie, International Edition (2015), 54 (29), 8449-8453CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Novel isoselenazoles with high glutathione peroxidase (GPx) and peroxiredoxin (Prx) activities provide remarkable cytoprotection to human cells, mainly by exhibiting antioxidant activities in the presence of cellular thiols. The cytotoxicity of the isoselenazoles is found to be significantly lower than that of ebselen, which is being clin. evaluated by several groups for the treatment of reperfusion injuries and stroke, hearing loss, and bipolar disorder. The compds. reported in this paper have the potential to be used as therapeutic agents for disorders mediated by reactive oxygen species.
  34. 34

    These samples were prepared by a procedure similar to that in Scheme 2a.

    There is no corresponding record for this reference.
  35. 35
    (a) Field, L.; Dilts, R. V.; Ravichandran, R.; Lenhert, P. G.; Carnahan, G. E. An Unusually Stable Thionitrite from N-Acetyl-D,L-Penicillamine; X-Ray Crystal and Molecular Structure of 2-(Acetylamino)-2-Carboxy-l,l-Dimethylethyl Thionitrite. J. Chem. Soc. Chem. Commun. 1978, 249– 250,  DOI: 10.1039/c39780000249
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    35a
    An unusually stable thionitrite from N-acetyl-D,L-penicillamine; x-ray crystal and molecular structure of 2-(acetylamino)-2-carboxy-1,1-dimethylethyl thionitrite
    Field, Lamar; Dilts, Robert V.; Ravichandran, Ramanathan; Lenhert, P. Galen; Carnahan, Gary E.
    Journal of the Chemical Society, Chemical Communications (1978), (6), 249-50CODEN: JCCCAT; ISSN:0022-4936.
    The structure of HO2CCH(NHAc)C(SR)Me2 (I; R = NO), prepd. (63%) from N-acetyl-DL-penicillamine (I; R = H) by reaction with HNO2, was detd. by x-ray anal. Refluxing of I (R = NO) in MeOH gave 100% [HO2CCH(NHAc)CMe2S]2. The homolytic and heterolytic reactions of I (R = NO) are described.
    (b) Yi, J.; Khan, M. A.; Lee, J.; Richter-Addo, G. B. The Solid-State Molecular Structure of the S-Nitroso Derivative of L-Cysteine Ethyl Ester Hydrochloride. Nitric Oxide 2005, 12, 261– 266,  DOI: 10.1016/j.niox.2005.03.005
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    The solid-state molecular structure of the S-nitroso derivative of L-cysteine ethyl ester hydrochloride
    Yi, Jun; Khan, Masood A.; Lee, Jonghyuk; Richter-Addo, George B.
    Nitric Oxide (2005), 12 (4), 261-266CODEN: NIOXF5; ISSN:1089-8603. (Elsevier)
    Nitrosation of protein sulfhydryl groups to form thionitrites (S-nitrosothiols) has been reported to be important in the biochem. of nitric oxide. Such S-nitrosation of protein thiol residues has been shown to alter the function of some proteins. In this brief communication, we report the x-ray crystal structure of S-nitroso-L-cysteine Et ester hydrochloride. Two rotamers with respect to the N-C-C-S moiety are present in the crystal: the major rotamer is in the gauche + conformation, and the minor rotamer is in the rare anti (trans, antiperiplanar) conformation for a cysteinyl compd. Importantly, the C-S-N=O groups for both rotamers are in the syn (cis, synperiplanar) form. To the best of our knowledge, this is the first reported high-resoln. solid-state structure of an S-nitroso deriv. of a cysteine or cysteinyl-contg. compd.
  36. 36
    (a) Bartberger, M. D.; Houk, K. N.; Powell, S. C.; Mannion, J. D.; Lo, K. Y.; Stamler, J. S.; Toone, E. J. Theory, Spectroscopy, and Crystallographic Analysis of S-Nitrosothiols: Conformational Distribution Dictates Spectroscopic Behavior. J. Am. Chem. Soc. 2000, 122, 5889– 5890,  DOI: 10.1021/ja994476y
    Google Scholar
    36a
    Theory, Spectroscopy, and Crystallographic Analysis of S-Nitrosothiols: Conformational Distribution Dictates Spectroscopic Behavior
    Bartberger, Michael D.; Houk, K. N.; Powell, Steven C.; Mannion, Joseph D.; Lo, Kenneth Y.; Stamler, Jonathan S.; Toone, Eric J.
    Journal of the American Chemical Society (2000), 122 (24), 5889-5890CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Exptl. (anti/syn ratios, 15N NMR chem. shift, and UV) and theor. [DFT, MP2, and QCISD(T) calcns. of optimized structures and anti/syn ratios and free energy differences, and GIAO calcn. of NMR chem. shifts] results establish the conformations of S-nitrosothiols. Revision of crystallog. structures and structure activity relations are warranted.
    (b) Zhao, Y.-L.; McCarren, P. R.; Houk, K. N.; Choi, B. Y.; Toone, E. J. Nitrosonium-Catalyzed Decomposition of S-Nitrosothiols in Solution: A Theoretical and Experimental Study. J. Am. Chem. Soc. 2005, 127, 10917– 10924,  DOI: 10.1021/ja050018f
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    36b
    Nitrosonium-Catalyzed Decomposition of S-Nitrosothiols in Solution: A Theoretical and Experimental Study
    Zhao, Yi-Lei; McCarren, Patrick R.; Houk, K. N.; Choi, Bo Yoon; Toone, Eric J.
    Journal of the American Chemical Society (2005), 127 (31), 10917-10924CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    The decompn. of S-nitrosothiols (RSNO) in soln. under oxidative conditions is significantly faster than can be accounted for by homolysis of the S-N bond. Here we propose a cationic chain mechanism in which nitrosation of nitrosothiol produces a nitrosated cation that, in turn, reacts with a second nitrosothiol to produce nitrosated disulfide and the NO dimer. The nitrosated disulfide acts as a source of nitrosonium for nitrosothiol nitrosation, completing the catalytic cycle. The mechanism accounts for several unexplained facets of nitrosothiol chem. in soln., including the observation that the decompn. of an RSNO is accelerated by O2, mixts. of O2 and NO, and other oxidants, that decompn. is inhibited by thiols and other antioxidants, that decompn. is dependent on sulfur substitution, and that decompn. often shows nonintegral kinetic orders.
  37. 37
    Cha, W.; Meyerhoff, M. E. Catalytic Generation of Nitric Oxide from S-Nitrosothiols Using Immobilized Organoselenium Species. Biomaterials 2007, 28, 19– 27,  DOI: 10.1016/j.biomaterials.2006.08.019
    Google Scholar
    37
    Catalytic generation of nitric oxide from S-nitrosothiols using immobilized organoselenium species
    Cha Wansik; Meyerhoff Mark E
    Biomaterials (2007), 28 (1), 19-27 ISSN:0142-9612.
    Novel nitric oxide (NO) generating polymeric materials possessing immobilized organoselenium species are described. These materials mimic the capability of small organoselenium molecules as well as a known selenium-containing enzyme, glutathione peroxidase (GPx), by catalytically decomposing S-nitrosothiols (RSNO) into NO and the corresponding free thiol. Model polymeric materials, e.g., cellulose filter paper and polyethylenimine, are modified with an appropriate diselenide species covalently linked to the polymeric structures. Such organoselenium (RSe)-derivatized polymers are shown to generate NO from RSNO species in the presence of an appropriate thiol reducing agent (e.g., glutathione). The likely involvement of both immobilized selenol/selenolate and diselenide species for NO production is suggested via a catalytic pathway, as deduced in separate homogeneous solution phase experiments using non-immobilized forms of small organodiselenide species. Preliminary experiments with the new RSe-polymers clearly demonstrate the ability of such materials to generate NO from RSNO species even after the contact with fresh animal plasma. It is anticipated that such NO generation from endogenous S-nitrosothiols in blood could render RSe-containing polymeric materials more thromboresistant when in contact with flowing blood, owing to NO's ability to inhibit platelet adhesion and activation.
  38. 38
    Kunwar, A.; Priyadarsini, K. I.; Jain, V. K. 3,3′-Diselenodipropionic Acid (DSePA): A Redox Active Multifunctional Molecule of Biological Relevance. Biochim. Biophys. Acta Gen. Subj. 2021, 1865, 129768,  DOI: 10.1016/j.bbagen.2020.129768
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    38
    3,3'-Diselenodipropionic acid (DSePA): A redox active multifunctional molecule of biological relevance
    Kunwar, A.; Priyadarsini, K. Indira; Jain, Vimal K.
    Biochimica et Biophysica Acta, General Subjects (2021), 1865 (1), 129768CODEN: BBGSB3; ISSN:0304-4165. (Elsevier B.V.)
    A review. Extensive research is being carried out globally to design and develop new selenium compds. for various biol. applications such as antioxidants, radio-protectors, anti-carcinogenic agents, biocides, etc. In this pursuit, 3,3'-diselenodipropionic acid (DSePA), a synthetic organoselenium compd., has received considerable attention for its biol. activities. This review intends to give a comprehensive account of research on DSePA so as to facilitate further research activities on this organoselenium compd. and to realize its full potential in different areas of biol. and pharmacol. sciences. It is an interesting diselenide structurally related to selenocystine. It shows moderate glutathione peroxidase (GPx)-like activity and is an excellent scavenger of reactive oxygen species (ROS). Exposure to radiation, as envisaged during radiation therapy, has been assocd. with normal tissue side effects and also with the decrease in selenium levels in the body. In vitro and in vivo evaluation of DSePA has confirmed its ability to reduce radiation induced side effects into normal tissues. Administration of DSePA through i.p. (IP) or oral route to mice in a dose range of 2 to 2.5 mg/kg body wt. has shown survival advantage against whole body irradn. and a significant protection to lung tissue against thoracic irradn. Pharmacokinetic profiling of DSePA suggests its max. absorption in the lung. Research work on DSePA reported in fifteen years or so indicates that it is a promising multifunctional organoselenium compd. exhibiting many important activities of biol. relevance apart from radioprotection.
  39. 39
    Yang, Z.; Yang, Y.; Xiong, K.; Li, X.; Qi, P.; Tu, Q.; Jing, F.; Weng, Y.; Wang, J.; Huang, N. Nitric Oxide Producing Coating Mimicking Endothelium Function for Multifunctional Vascular Stents. Biomaterials 2015, 63, 80– 92,  DOI: 10.1016/j.biomaterials.2015.06.016
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    39
    Nitric oxide producing coating mimicking endothelium function for multifunctional vascular stents
    Yang, Zhilu; Yang, Ying; Xiong, Kaiqin; Li, Xiangyang; Qi, Pengkai; Tu, Qiufen; Jing, Fengjuan; Weng, Yajun; Wang, Jin; Huang, Nan
    Biomaterials (2015), 63 (), 80-92CODEN: BIMADU; ISSN:0142-9612. (Elsevier Ltd.)
    The continuous release of nitric oxide (NO) by the native endothelium of blood vessels plays a substantial role in the cardiovascular physiol., as it influences important pathways of cardiovascular homeostasis, inhibits vascular smooth muscle cell (VSMC) proliferation, inhibits platelet activation and aggregation, and prevents atherosclerosis. In this study, a NO-catalytic bioactive coating that mimics this endothelium functionality was presented as a hemocompatible coating with potential to improve the biocompatibility of vascular stents. The NO-catalytic bioactive coating was obtained by covalent conjugation of 3,3-diselenodipropionic acid (SeDPA) with glutathione peroxidase (GPx)-like catalytic activity to generate NO from S-nitrosothiols (RSNOs) via specific catalytic reaction. The SeDPA was immobilized to an amine bearing plasma polymd. allylamine (PPAam) surface (SeDPA-PPAam). It showed long-term and continuous ability to catalytically decomp. endogenous RSNO and generate NO. The generated NO remarkably increased the cGMP synthesis both in platelets and human umbilical artery smooth muscle cells (HUASMCs). The surface exhibited a remarkable suppression of collagen-induced platelet activation and aggregation. It suppressed the adhesion, proliferation and migration of HUASMCs. Addnl., it was found that the NO catalytic surface significantly enhanced human umbilical vein endothelial cell (HUVEC) adhesion, proliferation and migration. The in vivo results indicated that the NO catalytic surface created a favorable microenvironment of competitive growth of HUVECs over HUASMCs for promoting re-endothelialization and reducing restenosis of stents in vivo.
  40. 40
    Höfler, L.; Meyerhoff, M. E. Modeling the Effect of Oxygen on the Amperometric Response of Immobilized Organoselenium-Based S-Nitrosothiol Sensors. Anal. Chem. 2011, 83, 619– 624,  DOI: 10.1021/ac1021979
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    40
    Modeling the Effect of Oxygen on the Amperometric Response of Immobilized Organoselenium-Based S-Nitrosothiol Sensors
    Hofler, Lajos; Meyerhoff, Mark E.
    Analytical Chemistry (Washington, DC, United States) (2011), 83 (2), 619-624CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
    Amperometric detection of S-nitrosothiols (RSNOs) at submicromolar levels in blood samples is of potential importance for monitoring endothelial function and other disease states that involve changes in physiol. nitric oxide (NO) prodn. It is shown here that the elimination of dissolved oxygen from samples is crit. when covalently attached diselenocystamine-based amperometric RSNO sensors are used for practical RSNO measurements. The newest generation of RSNO sensors utilizes an amperometric NO gas sensor with a thin organoselenium modified dialysis membrane mounted at the distal sensing tip. Sample RSNOs are catalytically reduced to NO within the dialysis membrane by the immobilized organoselenium species. In the presence of oxygen, the sensitivity of these sensors for measuring low levels of RSNOs (<μM) is greatly reduced. It is demonstrated that the main scavenger of the generated nitric oxide is not the dissolved oxygen but rather superoxide anion radical generated from the reaction of the reduced organoselenium species (the reactive species in the catalytic redox cycle) and dissolved oxygen. Computer simulations of the response of the RSNO sensor using rate consts. and diffusion coeffs. for the reactions involved, known from the literature or estd. from fitting to the obsd. amperometric response curves, as well as the specific geometric dimensions of the RSNO sensor, further support that nitric oxide and superoxide anion radical quickly react resulting in near zero sensor sensitivity toward RSNO concns. in the submicromolar concn. range. Elimination of oxygen from samples helps improve sensor detection limits to ∼10 nM levels of RSNOs.
  41. 41
    Cha, W.; Meyerhoff, M. E. Catalytic Generation of Nitric Oxide from S-Nitrosothiols Using Immobilized Organoselenium Species. Biomaterials 2007, 28, 19– 27,  DOI: 10.1016/j.biomaterials.2006.08.019
    Google Scholar
    41
    Catalytic generation of nitric oxide from S-nitrosothiols using immobilized organoselenium species
    Cha Wansik; Meyerhoff Mark E
    Biomaterials (2007), 28 (1), 19-27 ISSN:0142-9612.
    Novel nitric oxide (NO) generating polymeric materials possessing immobilized organoselenium species are described. These materials mimic the capability of small organoselenium molecules as well as a known selenium-containing enzyme, glutathione peroxidase (GPx), by catalytically decomposing S-nitrosothiols (RSNO) into NO and the corresponding free thiol. Model polymeric materials, e.g., cellulose filter paper and polyethylenimine, are modified with an appropriate diselenide species covalently linked to the polymeric structures. Such organoselenium (RSe)-derivatized polymers are shown to generate NO from RSNO species in the presence of an appropriate thiol reducing agent (e.g., glutathione). The likely involvement of both immobilized selenol/selenolate and diselenide species for NO production is suggested via a catalytic pathway, as deduced in separate homogeneous solution phase experiments using non-immobilized forms of small organodiselenide species. Preliminary experiments with the new RSe-polymers clearly demonstrate the ability of such materials to generate NO from RSNO species even after the contact with fresh animal plasma. It is anticipated that such NO generation from endogenous S-nitrosothiols in blood could render RSe-containing polymeric materials more thromboresistant when in contact with flowing blood, owing to NO's ability to inhibit platelet adhesion and activation.
  42. 42

    We previously reported the generation of BpqSeNO by transnitrosation from S-nitrosoglutathione (GSNO) (ref (14)). It was also confirmed that treatment of 4b with GSNO afforded 2b in conversion yield of ca. 30% (Scheme S12).

    There is no corresponding record for this reference.

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  • Abstract

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    Figure 1

    Figure 1. Previous works on Se-nitrososelenols and conceptual illustration of this study.

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    Figure 2

    Figure 2. Cradled selenocysteines that bear the Bpsc group (A) and the DB-Bpsc group (B).

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    Scheme 1

    Scheme 1. Synthesis of 4b and 5b
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    Figure 3

    Figure 3. Crystal structure of 5b (one of the two independent molecules).

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    Figure 4

    Figure 4. (a) Se-nitrosation of 4b. (b) 1H NMR spectrum (500 MHz, THF-d8) of 2b. (c) 77Se NMR spectrum (95 MHz, CDCl3) of 2b. (d) UV–vis (CDCl3) spectrum of 2b.

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    Scheme 2

    Scheme 2. Investigation of the Stability of Sec–SeNO 2b
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    Scheme 3

    Scheme 3. Model Reactions of Sec–SeNO with Thiols
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    Figure 5

    Figure 5. (a) Se-nitrosation of 4a. (b) 1H NMR spectrum (500 MHz, THF-d8) of 2a. (c) Diselenide-catalyzed NO generation from Cys–SNO.

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  • References

    This article references 42 other publications.

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      (a) Mustacich, D.; Powis, G. Thioredoxin Reductase. Biochem. J. 2000, 346, 1– 8,  DOI: 10.1042/bj3460001
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      A review with 105 refs. The mammalian thioredoxin reductases (TrxRs) are a family of Se-contg. pyridine nucleotide-disulfide oxidoreductases with mechanistic and sequence identity, including a conserved -Cys-Val-Asn-Val-Gly-Cys- redox catalytic site, to glutathione reductases. TrxRs catalyze the NADPH-dependent redn. of the redox protein, thioredoxin (Trx), as well as of other endogenous and exogenous compds. The broad substrate specificity of mammalian TrxRs is due to a 2nd redox-active site, a C-terminal -Cys-SeCys- (where SeCys is selenocysteine), that is not found in glutathione reductase or Escherichia coli TrxR. There are currently 2 confirmed forms of mammalian TrxRs (TrxR1 and TrxR2), and it is possible that other forms will be identified. The availability of Se is a key factor detg. TrxR activity both in cell culture and in vivo, and the mechanism(s) for the incorporation of Se into TrxRs, as well as the regulation of TrxR activity, have only recently begun to be investigated. The importance of Trx to many aspects of cell function make it likely that TrxRs also play a role in protection against oxidant injury, cell growth and transformation, and the recycling of ascorbate from its oxidized form. Since TrxRs are able to reduce a no. of substrates other than Trx, it is likely that addnl. biol. effects will be discovered for TrxR. Furthermore, inhibiting TrxR with drugs may lead to new treatments for human diseases such as cancer, AIDS, and autoimmune diseases.
      (b) Arnér, J.E. S. Focus on mammalian thioredoxin reductases─Important selenoproteins with versatile functions. Biochim. Biophys. Acta, Gen. Subj. 2009, 1790, 495– 526,  DOI: 10.1016/j.bbagen.2009.01.014
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      Focus on mammalian thioredoxin reductases - Important selenoproteins with versatile functions
      Arner, Elias S. J.
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      A review. Thioredoxin systems, involving redox-active thioredoxins and thioredoxin reductases, sustain a no. of important thioredoxin-dependent pathways. These redox-active proteins support several processes crucial for cell function, cell proliferation, antioxidant defense, and redox-regulated signaling cascades. Mammalian thioredoxin reductases are Se-contg. flavoprotein oxidoreductases, dependent upon a selenocysteine residue for redn. of the active site disulfide in thioredoxins. Their activity is required for normal thioredoxin function. The mammalian thioredoxin reductases also display surprisingly multifaceted properties and functions beyond thioredoxin redn. Expressed from 3 sep. genes (in humans named TXNRD1, TXNRD2, and TXNRD3), the thioredoxin reductases can each reduce a no. of different types of substrates in different cellular compartments. Their expression patterns involve intriguingly complex transcriptional mechanisms resulting in several splice variants, encoding a no. of protein variants likely to have specialized functions in a cell- and tissue-type restricted manner. The thioredoxin reductases are also targeted by a no. of drugs and compds. having an impact on cell function and promoting oxidative stress, some of which are used in treatment of rheumatoid arthritis, cancer, or other diseases. However, potential specific or essential roles for different forms of human or mouse thioredoxin reductases in health or disease are still rather unclear, although it is known that at least the murine Txnrd1 and Txnrd2 genes are essential for normal development during embryogenesis. This review is a survey of current knowledge of mammalian thioredoxin reductase function and expression, with a focus on human and mouse and a discussion of the striking complexity of these proteins. Several yet open questions regarding their regulation and roles in different cells or tissues are emphasized. It is concluded that the intriguingly complex regulation and function of mammalian thioredoxin reductases within the cellular context and in intact mammals strongly suggests that their functions are highly fine-tuned with the many pathways involving thioredoxins and thioredoxin-related proteins. These selenoproteins furthermore propagate many functions beyond a redn. of thioredoxins. Aberrant regulation of thioredoxin reductases, or a particular dependence upon these enzymes in diseased cells, may underlie their presumed therapeutic importance as enzymic targets using electrophilic drugs. These reductases are also likely to mediate several of the effects on health and disease that are linked to different levels of nutritional Se intake. The thioredoxin reductases and their splice variants may be pivotal components of diverse cellular signaling pathways, having importance in several redox-related aspects of health and disease. Clearly, a detailed understanding of mammalian thioredoxin reductases is necessary for a full comprehension of the thioredoxin system and of selenium dependent processes in mammals.
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      Freedman, Jane E.; Frei, Balz; Welch, George N.; Loscalzo, Joseph
      Journal of Clinical Investigation (1995), 96 (1), 394-400CODEN: JCINAO; ISSN:0021-9738. (Rockefeller University Press)
      GSH peroxidase (Px) catalyzes the redn. of lipid hydroperoxides (LOOH), known metabolic products of platelets and vascular cells. Because interactions between these cells are modulated by nitric oxide (NO) and LOOH inactivate NO, the authors investigated the effect of GSH-Px on the inhibition of platelet function by the naturally occurring S-nitrosothiol, S-nitrosoglutathione (SNO-Glu). Concns. of SNO-Glu that alone did not inhibit platelet function (subthreshold inhibitory concns.) were added to platelet-rich plasma together with GSH-Px (0.2-20 U/mL); this led to a dose-dependent inhibition of platelet aggregation with an IC50 of 0.6 U/mL GSH-Px. In the presence of subthreshold inhibitory concns. of SNO-Glu, the LOOH, 5-hydroperoxy-6,8,11,14-eicosatetraenoic acid, increased platelet aggregation, an effect reversed by GSH-Px. Glutathione and SNO-Glu were equally reversed by GSH-Px. Glutathione and SNO-Glu were equally effective as cosubstrates for GSH-Px. Incubation of SNO-Glu with GSH-Px for 1 min led to a 48.5% decrease in the concn. of SNO-Glu. Incubation of SNO-Glu with serum albumin led to the formation of S-nitroso-albumin, an effect enhanced by GSH-Px. These observations suggest that GSH-Px has two functions: redn. of LOOH, thereby preventing inactivation of NO, and metab. of SNO-Glu, thereby liberating NO and/or supporting further transnitrosation reactions.
      (b) Hou, Y.; Guo, Z.; Li, J.; Wang, P. G. Seleno Compounds and Glutathione Peroxidase Catalyzed Decomposition of S-Nitrosothiols. Biochem. Biophys. Res. Commun. 1996, 228, 88– 93,  DOI: 10.1006/bbrc.1996.1620
      5b
      Seleno compounds and glutathione peroxidase catalyzed decomposition of S-nitrosothiols
      Hou, Yongchun; Guo, Zhengmao; Li, Jun; Wang, Peng George
      Biochemical and Biophysical Research Communications (1996), 228 (1), 88-93CODEN: BBRCA9; ISSN:0006-291X. (Academic)
      Seleno compds. such as selenocystamine and seleno-D,L-cystine were found to catalyze the decompn. of S-nitrosothiols (e.g. S-nitroso-glutathione and S-nitroso-N-acetyl-D,L-penicillamine) in the presence of different thiols (e.g. glutathione, N-acetyl-D-penicillamine and 2-mercaptoethanol), and liberate nitric oxide. It was also found that glutathione peroxidase itself can catalyze the decompn. of S-nitroso-glutathione without the presence of any thiol or H2O2.
      (c) Igarashi, J.; Nishida, M.; Hoshida, S.; Yamashita, N.; Kosaka, H.; Hori, M.; Kuzuya, T.; Tada, M. Inducible Nitric Oxide Synthase Augments Injury Elicited by Oxidative Stress in Rat Cardiac Myocytes. Am. J. Physiol. Cell Physiol. 1998, 274, C245– C252,  DOI: 10.1152/ajpcell.1998.274.1.C245
      There is no corresponding record for this reference.
    6. 6
      (a) Asahi, M.; Fujii, J.; Suzuki, K.; Seo, H. G.; Kuzuya, T.; Hori, M.; Tada, M.; Fujii, S.; Taniguchi, N. Inactivation of Glutathione Peroxidase by Nitric Oxide: Implication for Cytotoxicity. J. Biol. Chem. 1995, 270, 21035– 21039,  DOI: 10.1074/jbc.270.36.21035
      6a
      Inactivation of glutathione peroxidase by nitric oxide. Implication for cytotoxicity
      Asahi, Michio; Fujii, Junichi; Suzuki, Keiichiro; Seo, Han Geuk; Kuzuya, Tsunehiko; Hori, Masatsugu; Tada, Michihiko; Fujii, Shigeru; Taniguchi, Naoyuki
      Journal of Biological Chemistry (1995), 270 (36), 21035-9CODEN: JBCHA3; ISSN:0021-9258. (American Society for Biochemistry and Molecular Biology)
      S-nitro-N-acetyl-DL-penicillamine (SNAP), a nitric oxide (NO) donor, inactivated bovine glutathione peroxidase (GPx) in a dose- and time-dependent manner. The IC50 of SNAP for GPx was 2 μM at 1 h of incubation and was 20% of the IC50 for another thiol enzyme, glyceraldehyde-3-phosphate dehydrogenase, in which a specific cysteine residue is known to be nitrosylated. Incubation of the inactivated GPx with 5 mM dithiothreitol within 1 h restored about 50% of activity of the start of the SNAP incubation. A longer exposure to NO donors, however, irreversibly inactivated the enzyme. The similarity of the inactivation with SNAP and reactivation with dithiothreitol of GPx to that of glyceraldehyde-3-phosphate dehydrogenase, suggested that NO released from SNAP modified a cysteine-like essential residue on GPx. When U937 cells were incubated with 100 μM SNAP for 1 h, a significant decrease in GPx activity was obsd. although the change was less dramatic than that with the purified enzyme, and intracellular peroxide levels increased as judged by flow cytometric anal. using a peroxide-sensitive dye. Other major antioxidative enzymes, copper/zinc superoxide dismutase, manganese superoxide dismutase, and catalase, were not affected by SNAP, which suggested that the increased accumulation of peroxides in SNAP-treated cells was due to inhibition of GPx activity by NO. Moreover, stimulation with lipopolysaccharide significantly decreased intracellular GPx activity in RAW 264.7 cells, and this effect was blocked by NO synthase inhibitor Nω-methyl-L-arginine. This indicated that GPx was also inactivated by endogenous NO. This mechanism may at least in part explain the cytotoxic effects of NO on cells and NO-induced apoptotic cell death.
      (b) Asahi, M.; Fujii, J.; Takao, T.; Kuzuya, T.; Hori, M.; Shimonishi, Y.; Taniguchi, N. The Oxidation of Selenocysteine Is Involved in the Inactivation of Glutathione Peroxidase by Nitric Oxide Donor. J. Biol. Chem. 1997, 272, 19152– 19157,  DOI: 10.1074/jbc.272.31.19152
      6b
      The oxidation of selenocysteine is involved in the inactivation of glutathione peroxidase by nitric oxide donor
      Asahi, Michio; Fujii, Junichi; Takao, toshifumi; Kuzuya, Tsunehiko; Hori, Masatsugu; Shimonishi, Yasutsugu; Taniguchi, Naoyuki
      Journal of Biological Chemistry (1997), 272 (31), 19152-19157CODEN: JBCHA3; ISSN:0021-9258. (American Society for Biochemistry and Molecular Biology)
      Glutathione peroxidase (GPx) was inactivated by S-nitroso-N-acetyl-D,L-penicillamine (SNAP), a nitric oxide donor. The structural basis of the inactivation was studied. We also show that 3-morpholinosydnonimine N-ethylcarbamide, a peroxynitrite precursor, as well as synthetic peroxynitrite also inactivated bovine GPx. The degree of incorporation of a sulfhydryl reagent, n-octyldithionitrobenzoic acid, into GPx decreased after pretreatment with SNAP as evidenced by mass spectrometry. To identify the modification site of this enzyme by SNAP, both SNAP-pretreated and untreated GPxs were reacted with n-octyldithionnitrobenzoic acid and digested with lysylendopeptidase, and the resulting peptides were subjected to mass spectrometry. This technique identified a bridge between two peptides, one of which contains Sec45 at the catalytic center and Cys74, and the other contains Cys91. Although there are two possible combinations, selenocystine 45 (Sec45) and Cys91 or Cys74 and Cys91, the tertiary structure of GPx indicates that a cross-link between Sec45 and Cys91 is more feasible. This is consistent with the exptl. evidence that SNAP specifically inactivates GPx, in which Sec45 forms the catalytic center. Thus, we conclude that SNAP mainly oxidized Sec45 to form a selenenyl sulfide (Se-S) with a free thiol, leading to the inactivation of the enzyme. These data suggest that nitric oxide and its derivs. directly inactivate GPx in a specific manner via the prodn. of a selenenyl sulfide, resulting in an increase in intracellular peroxides that are responsible for cellular damage.
      (c) Fujii, J.; Taniguchi, N. Down regulation of superoxide dismutases and glutathione peroxidase by reactive oxygen and nitrogen species. Free Radical Res. 1999, 31, 301– 308,  DOI: 10.1080/10715769900300861
      6c
      Down regulation of superoxide dismutases and glutathione peroxidase by reactive oxygen and nitrogen species
      Fujii, Junichi; Taniguchi, Naoyuki
      Free Radical Research (1999), 31 (4), 301-308CODEN: FRARER; ISSN:1071-5762. (Harwood Academic Publishers)
      A review, with 42 refs. The levels of antioxidative enzymes are regulated by gene expressions as well as by post-translational modifications. Although their functions are to scavenge reactive oxygen (ROS) and nitrogen species (RNS), they may also be targets of various oxidants. When ROS and RNS modify the functions of antioxidative enzymes, esp. glutathione peroxidase, they may induce apoptotic cell death in susceptible cells. It is conceivable, therefore, that at least a part of the apoptotic pathways mediated by ROS and RNS may be assocd. with modification of the redox regulation of cellular functions due to elevations of such substances. In this article we review recent findings about the effects of various oxidative conditions assocd. with alteration of these antioxidative enzymes and the concomitant cellular damage induced.
      (d) Koh, H. Y.; Suzuki, K.; Che, W.; Park, Y. S.; Miyamoto, Y.; Higashiyama, S.; Taniguchi, N. Inactivation of Glutathione Peroxidase by Nitric Oxide Leads to the Accumulation of H2O2 and the Induction of HB-EGF via c-Jun NH2-Terminal Kinase in Rat Aortic Smooth Muscle Cells. FASEB J. 2001, 15, 1335– 1492,  DOI: 10.1096/fj.00-0572fje
      There is no corresponding record for this reference.
    7. 7
      Nikitovic, D.; Holmgren, A. S-Nitrosoglutathione Is Cleaved by the Thioredoxin System with Liberation of Glutathione and Redox Regulating Nitric Oxide. J. Biol. Chem. 1996, 271, 19180– 19185,  DOI: 10.1074/jbc.271.32.19180
      7
      S-nitrosoglutathione is cleaved by the thioredoxin system with liberation of glutathione and redox regulating nitric oxide
      Nikitovic, Dragana; Holmgren, Arne
      Journal of Biological Chemistry (1996), 271 (32), 19180-19185CODEN: JBCHA3; ISSN:0021-9258. (American Society for Biochemistry and Molecular Biology)
      In activated human neutrophils a burst of nitric oxide (NO) converts intracellular GSH to S-nitrosoglutathione (GSNO) which is subsequently cleaved to restore GSH by an unknown mechanism. We discovered that GSNO is an NADPH oxidizing substrate for human or calf thymus thioredoxin reductase (TR) with an apparent Km value of 60 μM and a Kcat of 0.6 × s-1. Addn. of human thioredoxin (Trx) stimulated the initial NADPH oxidn. rate severalfold but was accompanied by progressive inactivation of TR. Escherichia coli TR lacked activity with GSNO, but with E. coli Trx present, GSNO was reduced without inhibition of the enzyme. Chem. reduced E. coli Trx-(SH)2 was oxidized to Trx-S2 by GSNO with a rate const. of 760 M-1S-1 (7-fold faster than by GSSG) as measured by tryptophan fluorescence. Anal. of this reaction in the presence of oxymyoglobin revealed quant. formation of metmyoglobin indicative of NO. release. Anal. of GSNO redn. demonstrated that oxidn. of NADPH produced a stoichiometric amt. of free GSH. These results demonstrate a homolytic cleavage mechanism of GSNO, giving rise to GSH and NO. GSNO efficiently inhibited the protein disulfide reductase activity of the complete human or calf thymus thioredoxin systems. Our results demonstrate enzymic cleavage of GSNO by TR or Trx and suggest novel mechanisms for redox signaling.
    8. 8
      (a) Engelman, R.; Ziv, T.; Arnér, E. S. J.; Benhar, M. Inhibitory nitrosylation of mammalian thiredoxin reductase 1: Molecular characterization and evidence for its functional role in cellular nitroso-redox imbalance. Free Radic. Biol. Med. 2016, 97, 375– 385,  DOI: 10.1016/j.freeradbiomed.2016.06.032
      8a
      Inhibitory nitrosylation of mammalian thioredoxin reductase 1: Molecular characterization and evidence for its functional role in cellular nitroso-redox imbalance
      Engelman, Rotem; Ziv, Tamar; Arner, Elias S. J.; Benhar, Moran
      Free Radical Biology & Medicine (2016), 97 (), 375-385CODEN: FRBMEH; ISSN:0891-5849. (Elsevier B.V.)
      Mammalian thioredoxin 1 (Trx1) and the selenoprotein Trx reductase 1 (TrxR1) are key cellular enzymes that function coordinately in thiol-based redox regulation and signaling. Recent studies have revealed that the Trx1/TrxR1 system has an S-nitrosothiol reductase (denitrosylase) activity through which it can regulate nitric oxide-related cellular processes. In this study we revealed that TrxR1 is itself susceptible to nitrosylation, characterized the underlying mechanism, and explored its functional significance. We found that nitrosothiol or nitric oxide donating agents rapidly and effectively inhibited the activity of recombinant or endogenous TrxR1. In particular, the NADPH-reduced TrxR1 was partially and reversibly inhibited upon exposure to low concns. (<10 μM) of S-nitrosocysteine (CysNO) and markedly and continuously inhibited at higher doses. Concurrently, TrxR1 very efficiently reduced low, but not high, levels of CysNO. Biochem. and mass spectrometric analyses indicated that its active site selenocysteine residue renders TrxR1 highly susceptible to nitrosylation-mediated inhibition, and revealed both thiol and selenol modifications at the two redox active centers of the enzyme. Studies in HeLa cancer cells demonstrated that endogenous TrxR1 is sensitive to nitrosylation-dependent inactivation and pointed to an important role for glutathione in reversing or preventing this process. Notably, depletion of cellular glutathione with L-buthionine-sulfoximine synergized with nitrosating agents in promoting sustained nitrosylation and inactivation of TrxR1, events that were accompanied by significant oxidn. of Trx1 and extensive cell death. Collectively, these findings expand our knowledge of the role and regulation of the mammalian Trx system in relation to cellular nitroso-redox imbalance. The observations raise the possibility of exploiting the nitrosylation susceptibility of TrxR1 for killing tumor cells.
      (b) Benhar, M. Roles of Mammalian Glutathione Peroxidase and Thioredoxin Reductase Enzymes in the Cellular Response to Nitrosative Stress. Free Radic. Biol. Med. 2018, 127, 160– 164,  DOI: 10.1016/j.freeradbiomed.2018.01.028
      8b
      Roles of mammalian glutathione peroxidase and thioredoxin reductase enzymes in the cellular response to nitrosative stress
      Benhar, Moran
      Free Radical Biology & Medicine (2018), 127 (), 160-164CODEN: FRBMEH; ISSN:0891-5849. (Elsevier B.V.)
      A review. Mammalian cells employ elaborate antioxidant systems to effectively handle reactive oxygen and nitrogen species (ROS and RNS). At the heart of these systems operate two selenoprotein families consisting of glutathione peroxidase (GPx) and thioredoxin reductase (TrxR) enzymes. Although mostly studied in the context of oxidative stress, considerable evidence has amassed to indicate that these selenoenzymes also play important roles in nitrosative stress responses. GPx and TrxR, together with their redox partners, metabolize nitrosothiols and peroxynitrite, two major RNS. As such, these enzymes play active roles in the cellular defense against nitrosative stress. However, under certain conditions, these enzymes are inactivated by nitrosothiols or peroxynitrite, which may exacerbate oxidative and nitrosative stress in cells. The selenol groups in the active sites of GPx and TrxR enzymes are critically involved in these beneficial and detrimental processes. Further elucidation of the biochem. interactions between distinct RNS and GPx/TrxR will lead to a better understanding of the roles of these selenoenzymes in cellular homeostasis and disease.
    9. 9
      Dobashi, K.; Asayama, K.; Nakane, T.; Kodera, K.; Hayashibe, H.; Nakazawa, S. Induction of glutathione peroxidase in response to inactivation by nitric oxide. Free Radical Res. 2001, 35, 319– 327,  DOI: 10.1080/10715760100300851
      9
      Induction of glutathione peroxidase in response to inactivation by nitric oxide
      Dobashi, Kazushige; Asayama, Kohtaro; Nakane, Takaya; Kodera, Koji; Hayashibe, Hidemasa; Nakazawa, Shinpei
      Free Radical Research (2001), 35 (3), 319-327CODEN: FRARER; ISSN:1071-5762. (Harwood Academic Publishers)
      To det. the effect of nitric oxide (NO) on cellular glutathione peroxidase (GPX) levels in living cells, we measured the activity, protein and mRNA of GPX in rat kidney (KNRK) cells under a high NO condition. Combined treatment of lipopolysaccharide (LPS, 1 μg/mL) and tumor necrosis factor-α (TNF-α, 50 ng/mL) synergistically enhanced (23-folds) nitrite prodn. from KNRK cells. This was suppressed by an inducible NO synthase (iNOS) inhibitor (aminoguanidine, N-nitro-L-arginine methylester hydrochloride) and arginase. INOS expression was detected by RT-PCR in the treated cells. GPX was inactivated irreversibly when the cells had been homogenized before exposure to the NO donor, S-nitroso-N-acetylpenicillamine (SNAP). In living KNRK cells, SNAP and LPS + TNF-α exerted a transient effect on the GPX activity. The treatment with SNAP (200 μM) or sodium nitroprusside (200 μM) enhanced GPX gene expression, which was blocked by a NO scavenger, 2-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-oxide. GPX mRNA was markedly increased by the treatment with LPS + TNF-α, and aminoguanidine blocked the effect. In cells metabolically labeled with 75Se, LPS + TNF-α accelerated the incorporation of radioactivity into GPX mols. by 2.1-fold. These results suggest that inactivation of GPX by NO triggers a signal for inducing GPX gene expression in KNRK cells, thereby restoring the intracellular level of this indispensable enzyme.
    10. 10
      Lai, C.-H.; Chou, P.-T. The Theoretical Comparison between Two Model NO Carriers, MeSNO and MeSeNO. J. Mol. Model. 2008, 14, 1– 9,  DOI: 10.1007/s00894-007-0246-z
      10
      The theoretical comparison between two model NO carriers, MeSNO and MeSeNO
      Lai, Chin-Hung; Chou, Pi-Tai
      Journal of Molecular Modeling (2008), 14 (1), 1-9CODEN: JMMOFK; ISSN:0948-5023. (Springer GmbH)
      In this study, we apply a hybrid DFT functional, MPW1LYP, to make a comparison between MeSNO and MeSeNO. Due to the mesomeric effect and neg. hyperconjugation, Se-nitrososelenols seem to be more unstable than S-nitrosothiols regarding unimol. decompn. Interestingly, however, the barrier of the transnitrosation reaction of MeSeNO is larger than that of MeSNO, disregarding nucleophiles in the gas phase. Using the polarizable continuum model to consider the water solvent effect, the transnitrosation reactions of MeXNO and YMe- (X = S, Se; Y = S, Se) are found to undergo concerted reactions, in sharp contrast to the two-step reaction pathways concluded in the gas phase. Moreover, the barriers of the transnitrosation reactions of MeSNO for nucleophiles SMe- and SeMe- from the gas phase to the aq. soln. are found to be decreased, while the transnitrosation reactions of MeSeNO are essentially barrierless in aq. soln.
    11. 11
      (a) Flohé, L. Glutathione Peroxidase Brought into Focus. In Free Radicals in Biology; Pryor, A. W., Ed.; Academic Press: 1982.
      There is no corresponding record for this reference.
      (b) Epp, O.; Ladenstein, R.; Wendel, A. The Refined Structure of the Selenoenzyme Glutathione Peroxidase at 0.2-nm Resolution. Eur. J. Biochem. 1983, 133, 51– 69,  DOI: 10.1111/j.1432-1033.1983.tb07429.x
      11b
      The refined structure of the selenoenzyme glutathione peroxidase at 0.2-nm resolution
      Epp, Otto; Ladenstein, Rudolf; Wendel, Albrecht
      European Journal of Biochemistry (1983), 133 (1), 51-69CODEN: EJBCAI; ISSN:0014-2956.
      The crystal structure of bovine erythrocyte glutathione peroxidase (I) was refined by a combined procedure of restrained crystallog. refinement and energy minimization at 0.2 nm resoln. The structure at 0.28 nm resoln., which was detd. by multiple isomorphous replacement, served as a starting model. The refined model allowed a detailed survey of the H-bonding pattern and of the subunit contact areas in the mol. The model contained 165 solvent mols. per dimer, all taken as water mols. The mobility of the structure was derived from the individual at. temp. factors. The complete tetramer, including the active sites, appeared to be rather rigid, except for narrow loops near the N-terminal ends and some β turns exposed to solvent. The active centers of I were found in flat depressions on the mol. surface. The catalytically active selenocysteine residues could be located at the N-terminal ends of α helixes forming βαβ substructures together with 2 adjacent parallel β strands. In the vicinity of the reactive group, some arom. amino acid side-chains could be localized; esp. tryptophan-148, which could be H-bonded to selenocysteine-35 and may play a functional role during catalysis. The results of substrate and inhibitor binding studies in soln. and in the cryst. state could be interpreted by an apparent half-site reactivity of I. I appeared to react in the sense of neg. cooperativity with dimers being the functional units. Based on difference Fourier analyses of appropriate derivs., a reasonable model of glutathione binding is presented. Among the residues which could be of functional importance are arginine-40, glutamine-130, and arginine-167, presumably forming salt bridges and an H-bond to the glutathione mol. Thus, a general picture of a minimal reaction mechanism, which is in good agreement with functional and structural data, is proposed. The main reaction of the catalytic cycle presumably shuttles between the selenolate and the selenenic acid state of selenocysteine-35.
      (c) Maiorino, F. M.; Brigelius-Flohé, R.; Aumann, K. D.; Roveri, A.; Schomburg, D.; Flohé, L. Diversity of Glutathione Peroxidases. Methods Enzymol. 1995, 252, 38– 53,  DOI: 10.1016/0076-6879(95)52007-4
      11c
      Diversity of glutathione peroxidases
      Ursini, F.; Maiorino, M.; Brigelius-Flohe, R.; Aumann, K. D.; Roveri, A.; Schomburg, D.; Flohe, L.
      Methods in Enzymology (1995), 252 (Biothiols, Part B), 38-53, 6 platesCODEN: MENZAU; ISSN:0076-6879. (Academic)
      In this chapter, the authors compile the structural knowledge on various glutathione peroxidase types to provide a basis for discussion of the possible biol. meaning of the structural diversification within this family of selenoenzymes.
      (d) Brigelius-Flohé, R.; Maiorino, M. Glutathione Peroxidases. Biochim. Biophys. Acta 2013, 1830, 3289– 3303,  DOI: 10.1016/j.bbagen.2012.11.020
      11d
      Glutathione peroxidases
      Brigelius-Flohe, Regina; Maiorino, Matilde
      Biochimica et Biophysica Acta, General Subjects (2013), 1830 (5), 3289-3303CODEN: BBGSB3; ISSN:0304-4165. (Elsevier B.V.)
      A review. With increasing evidence that hydroperoxides are not only toxic but rather exert essential physiol. functions, hydroperoxide-removing enzymes need to be reviewed. In mammals, the peroxidases inter alia comprise the 8 glutathione peroxidases (GPx1-GPx8) so far identified. Since GPxs have recently been reviewed under various aspects, the authors here focus on novel findings considering their diverse physiol. roles exceeding an antioxidant activity. GPxs are involved in balancing H2O2 homeostasis in signaling cascades, e.g., in the insulin-signaling pathway by GPx1. GPx2 plays a dual role in carcinogenesis depending on the mode of initiation and cancer stage. GPx3 is membrane-assocd. possibly explaining a peroxidatic function despite low plasma concns. of GSH. GPx4 has novel roles in the regulation of apoptosis and, together with GPx5, in male fertility. The functions of GPx6 are still unknown, and the proposed involvement of GPx7 and GPx8 in protein folding awaits elucidation. Collectively, Se-contg. GPxs (GPx1-4 and Gpx6) as well as their non-selenium congeners (GPx5, GPx7, and GPx8) have become key players in important biol. contexts far beyond the detoxification of hydroperoxides.
    12. 12
      Perissinotti, L. L.; Turjanski, A. G.; Estrin, D. A.; Doctorovich, F. Transnitrosation of Nitrosothiols: Characterization of an Elusive Intermediate. J. Am. Chem. Soc. 2005, 127, 486– 487,  DOI: 10.1021/ja044056v
      12
      Transnitrosation of Nitrosothiols: Characterization of an Elusive Intermediate
      Perissinotti, Laura L.; Turjanski, Adrian G.; Estrin, Dario A.; Doctorovich, Fabio
      Journal of the American Chemical Society (2005), 127 (2), 486-487CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      We report an investigation of the reaction between (S)-nitroso-L-cysteine Et ester and L-cysteine Et ester as a model of physiol. relevant transnitrosation processes. Our theor. and exptl. evidence clearly supports the existence of a nitroxyl disulfide intermediate in soln.
    13. 13

      For recent reviews, see

      (a) Hess, T. D.; Matsumoto, A.; Kim, S.-O.; Marshall, E. H.; Stamler, J. S. Protein S-nitrosylation: purview and parameters. Nat. Rev. Mol. Cell. Biol. 2005, 6, 150– 166,  DOI: 10.1038/nrm1569
      13a
      Protein S-nitrosylation: purview and parameters
      Hess, Douglas T.; Matsumoto, Akio; Kim, Sung-Oog; Marshall, Harvey E.; Stamler, Jonathan S.
      Nature Reviews Molecular Cell Biology (2005), 6 (2), 150-166CODEN: NRMCBP; ISSN:1471-0072. (Nature Publishing Group)
      A review. Protein S-nitrosylation (thionitrosylation), the covalent attachment of a NO group to the thiol side-chain of Cys residues, has emerged as an important mechanism for dynamic, post-translational regulation of most or all main classes of protein. S-nitrosylation thereby conveys a large part of the ubiquitous influence of NO on cellular signal transduction, and provides a mechanism for redox-based physiol. regulation.
      (b) Nakamura, T.; Lipton, S. Redox modulation by S-nitrosylation contributes to protein misfolding, mitochondrial dynamics, and neuronal synaptic damage in neurodegenerative diseases. Cell Death Differ. 2011, 18, 1478– 1486,  DOI: 10.1038/cdd.2011.65
      13b
      Redox modulation by S-nitrosylation contributes to protein misfolding, mitochondrial dynamics, and neuronal synaptic damage in neurodegenerative diseases
      Nakamura, T.; Lipton, S. A.
      Cell Death and Differentiation (2011), 18 (9), 1478-1486CODEN: CDDIEK; ISSN:1350-9047. (Nature Publishing Group)
      A review. The pathol. processes of neurodegenerative disorders such as Alzheimer's and Parkinson's diseases engender synaptic and neuronal cell damage. While mild oxidative and nitrosative (nitric oxide (NO)-related) stress mediates normal neuronal signaling, excessive accumulation of these free radicals is linked to neuronal cell injury or death. In neurons, N-methyl--aspartate (NMDA) receptor (NMDAR) activation and subsequent Ca2+ influx can induce the generation of NO via neuronal NO synthase. Emerging evidence has demonstrated that S-nitrosylation, representing covalent reaction of an NO group with a crit. protein thiol, mediates the vast majority of NO signaling. Analogous to phosphorylation and other posttranslational modifications, S-nitrosylation can regulate the biol. activity of many proteins. Here, we discuss recent studies that implicate neuropathogenic roles of S-nitrosylation in protein misfolding, mitochondrial dysfunction, synaptic injury, and eventual neuronal loss. Among a growing no. of S-nitrosylated proteins that contribute to disease pathogenesis, in this review we focus on S-nitrosylated protein-disulfide isomerase (forming SNO-PDI) and dynamin-related protein 1 (forming SNO-Drp1). Furthermore, we describe drugs, such as memantine and newer derivs. of this compd. that can prevent both hyperactivation of extrasynaptic NMDARs as well as downstream pathways that lead to nitrosative stress, synaptic damage, and neuronal loss. Cell Death and Differentiation (2011) 18, 1478-1486; doi:10.1038/cdd.2011.65; published online 20 May 2011.
    14. 14
      Shimada, K.; Goto, K.; Kawashima, T.; Takagi, N.; Choe, Y.-K.; Nagase, S. Isolation of a Se-Nitrososelenol: A New Class of Reactive Nitrogen Species Relevant to Protein Se-Nitrosation. J. Am. Chem. Soc. 2004, 126, 13238– 13239,  DOI: 10.1021/ja0457009
      14
      Isolation of a Se-Nitrososelenol: A New Class of Reactive Nitrogen Species Relevant to Protein Se-Nitrosation
      Shimada, Keiichi; Goto, Kei; Kawashima, Takayuki; Takagi, Nozomi; Choe, Yoong-Kee; Nagase, Shigeru
      Journal of the American Chemical Society (2004), 126 (41), 13238-13239CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Nitric oxide (NO) is a messenger mol. implicated in a no. of physiol. processes. Nitrosation of selenoproteins has been suggested as playing an important role in NO-mediated cellular functions such as the inactivation of glutathione peroxidase (GPx), but no chem. information about Se-nitrosated species has been available to date. Here a stable Se-nitrososelenol (RSeNO), a new class of NO deriv., was synthesized and fully characterized by x-ray crystallog. and spectroscopic methods. This Se-nitrososelenol can be formed by direct transnitrosation from an S-nitrosothiol to a selenol, as is the case in the proposed mechanism for the NO-mediated inactivation of GPx.
    15. 15
      Shimada, K.; Goto, K.; Kawashima, T. Thermolysis and Photolysis of Stable Se-Nitrososelenols. Chem. Lett. 2005, 34, 654– 655,  DOI: 10.1246/cl.2005.654
      15
      Thermolysis and photolysis of stable Se-nitrososelenols
      Shimada, Keiichi; Goto, Kei; Kawashima, Takayuki
      Chemistry Letters (2005), 34 (5), 654-655CODEN: CMLTAG; ISSN:0366-7022. (Chemical Society of Japan)
      The stable sterically encumbered bowl-type Se-nitrososelenols undergo thermal and photochem. decompn. affording diselenides. Thermolysis of 2,6-Ar2C6H3SeNO [1, Ar = 3,5-bis(2,6-diisopropylphenyl)phenyl] afforded diselenide [2,6-Ar2C6H3Se]2 (3), the structure of which was detd. by x-ray crystallog., while tetraselenide 2,6-Ar2C6H3Se4C6H3Ar2-2,6 (13) was obtained as the major product in photolysis of 1. Thermolysis of 4-tBu-2,6-R2C6H2SeNO (2, R = 2,6-bis(2,6-dimethylphenyl)phenylmethyl) gave diselenide [4-tBu-2,6-R2C6H2Se]2 (12).
    16. 16
      Wismach, C.; du Mont, W.-W.; Jones, P. G.; Ernst, L.; Papke, U.; Mugesh, G.; Kaim, W.; Wanner, M.; Becker, K. D. Selenol Nitrosation and Se-Nitrososelenol Homolysis: A Reaction Path with Possible Biochemical Implications. Angew. Chem., Int. Ed. 2004, 43, 3970– 3974,  DOI: 10.1002/anie.200453872
      16
      Selenol nitrosation and Se-nitrososelenol homolysis: A reaction path with possible biochemical implications
      Wismach, Cathleen; du Mont, Wolf-Walther; Jones, Peter G.; Ernst, Ludger; Papke, Ulrich; Mugesh, Govindasamy; Kaim, Wolfgang; Wanner, Matthias; Becker, Klaus D.
      Angewandte Chemie, International Edition (2004), 43 (30), 3970-3974CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The nitrosation of selenols REH [E = Se, R = 2-(4,4-dimethyl-2-oxazolinyl)phenyl, (Me3Si)3Si] with tert-Bu nitrite at -78° generated the 1st Se-nitrososelenol, REN:O (2b and 4b, resp.), which were identified by IR spectroscopy and further proven by its 1,4-addn. to 2,3-dimethyl-1,3-butadiene. Compd. 2b decomps. rapidly to give diselenide R2E2. The expts. may give insight into the interactions of selenoproteins with NO in vivo.
    17. 17
      Song, L.; Keul, F.; Mardyukov, A. Preparation and Spectroscopic Identification of Methyl-Se-Nitrososelenol. Chem. Commun. 2019, 55, 9943– 9946,  DOI: 10.1039/C9CC05065E
      17
      Preparation and spectroscopic identification of methyl-Se-nitrososelenol
      Song, Lijuan; Keul, Felix; Mardyukov, Artur
      Chemical Communications (Cambridge, United Kingdom) (2019), 55 (67), 9943-9946CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      Herein, we report, for the first time, the prepn., matrix-isolation, and spectroscopic characterization of the Me selenyl radical and methyl-Se-nitrososelenol in combination with DFT and CASSCF/NEVPT2 computations. The latter proved to be highly photolabile, and upon irradn. with light at λ = 465 nm it leads to Me selenyl and nitric oxide radical pairs. Upon λ > 730 nm irradn. it rearranges back to methyl-Se-nitrososelenol.
    18. 18
      Reich, H. J.; Hoeger, C. A.; Willis, W.W. Organoselenium Chemistry : A Study of Intermediates in the Fragmentation of Aliphatic Ketoselenoxides. Characterization of Selenoxides, Selenenamides and Selenolseleninates by 1H-,13C- and 77Se-NMR. Tetrahedron 1985, 41, 4771– 4779,  DOI: 10.1016/S0040-4020(01)96716-X
      18
      Organoselenium chemistry. A study of intermediates in the fragmentation of aliphatic keto selenoxides. Characterization of selenoxides, selenenamides and selenol seleninates by proton, carbon-13 and selenium-77 NMR
      Reich, Hans J.; Hoeger, Carl A.; Willis, W. W. Jr.
      Tetrahedron (1985), 41 (21), 4771-9CODEN: TETRAB; ISSN:0040-4020.
      PhCOCMe2SeSe(O)CMe2COPh(I) was detected as an intermediate in the decompn. of PhCOCMe2Se(O)R [II, R = CMe2COPh, C(CH2Ph)(COMe)2]. I, which is stable in soln. below -50°, underwent thermal decompn. and reactions with P(OMe)3 to give (PhCOCMe2)Se2 and with Me2NH to give PhCOCMe2SeNMe2 as the major product. Decompn. of I in the presence of (PhCH2)2NH results in trapping PhCOCMe2SeSeOH to give PhCOCMe2SeSeN(CH2Ph)2. I could not be prepd. by oxidn. of (PhCOCMe2)2Se2. 1,2-Diselenolane III was prepd. by oxidn. of the corresponding diselenide. Cyclopropanes IV (R = OH R1 = H, Me) were generated from IV (R = CMe2COPh, C(COMe)2CH2Ph]. IV (R = CMe2COPh, R1 = H) underwent disproportionation to IV (R = OH, R1 = H) and diselenide V (R1 = H) even when prepd. at -49°. IV (R = CMe2COPh, R1 = Me) gave a selenol seleninate, which disproportionated at -17° to V (R1 = Me) and IV (R = OH, R1 = Me).
    19. 19
      Goto, K.; Nagahama, M.; Mizushima, T.; Shimada, K.; Kawashima, T.; Okazaki, R. The First Direct Oxidative Conversion of a Selenol to a Stable Selenenic Acid: Experimental Demonstration of Three Processes Included in the Catalytic Cycle of Glutathione Peroxidase. Org. Lett. 2001, 3, 3569– 3572,  DOI: 10.1021/ol016682s
      19
      The First Direct Oxidative Conversion of a Selenol to a Stable Selenenic Acid: Experimental Demonstration of Three Processes Included in the Catalytic Cycle of Glutathione Peroxidase
      Goto, Kei; Nagahama, Michiko; Mizushima, Tadashi; Shimada, Keiichi; Kawashima, Takayuki; Okazaki, Renji
      Organic Letters (2001), 3 (22), 3569-3572CODEN: ORLEF7; ISSN:1523-7060. (American Chemical Society)
      A stable selenenic acid, I (Z = SeOH: BmtSeOH), was synthesized by direct oxidn. of selenol, BmtSeH, bearing a novel bowl-type substituent with H2O2, and its structure was established by x-ray crystallog. anal. Selenenyl sulfides obtained by the reaction of the selenenic acid with 1,4-dithiols were reduced to the corresponding selenol by treatment with a tertiary amine, thus achieving the exptl. demonstration of three processes included in the catalytic cycle of glutathione peroxidase.
    20. 20
      (a) Masuda, R.; Kimura, R.; Karasaki, T.; Sase, S.; Goto, K. Modeling the Catalytic Cycle of Glutathione Peroxidase by Nuclear Magnetic Resonance Spectroscopic Analysis of Selenocysteine Selenenic Acids. J. Am. Chem. Soc. 2021, 143, 6345– 6350,  DOI: 10.1021/jacs.1c02383
      20a
      Modeling the catalytic cycle of glutathione peroxidase by nuclear magnetic resonance spectroscopic analysis of selenocysteine selenenic acids
      Masuda, Ryosuke; Kimura, Ryutaro; Karasaki, Takafumi; Sase, Shohei; Goto, Kei
      Journal of the American Chemical Society (2021), 143 (17), 6345-6350CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Although selenocysteine selenenic acids (Sec-SeOHs) have been recognized as key intermediates in the catalytic cycle of glutathione peroxidase (GPx), examples of the direct observation of Sec-SeOH in either protein or small-mol. systems have remained elusive so far, mostly due to their instability. Here, we report the first direct spectroscopic (1H and 77Se NMR) evidence for the formation of Sec-SeOH in small-mol. selenocysteine and selenopeptide model systems with a cradle-type protective group. The catalytic cycle of GPx was investigated using NMR-observable Sec-SeOH models. All the hitherto proposed chem. processes, i.e., not only those of the canonical catalytic cycle but also those involved in the bypass mechanism, including the intramol. cyclization of Sec-SeOH to the corresponding five-membered ring selenenyl amide, were examd. in a stepwise manner.
      (b) Masuda, R.; Goto, K. Modeling of selenocysteine-derived reactive intermediates utilizing a nano-sized molecular cavity as a protective cradle. Methods Enzymol. 2022, 662, 331– 361,  DOI: 10.1016/bs.mie.2021.10.018
      20b
      Modeling of selenocysteine-derived reactive intermediates utilizing a nano-sized molecular cavity as a protective cradle
      Masuda, Ryosuke; Goto, Kei
      Methods in Enzymology (2022), 662 (Selenoprotein Structure and Function), 331-361CODEN: MENZAU; ISSN:1557-7988. (Elsevier Inc.)
      In the biol. functions of selenoproteins, various highly reactive species formed by oxidative modification of selenocysteine residues have been postulated to play crucial roles. Representative examples of such species are selenocysteine selenenic acids (Sec-SeOHs) and selenocysteine selenenyl iodides (Sec-SeIs), which have been widely recognized as important intermediates in the catalytic cycle of glutathione peroxidase (GPx) and iodothyronine deiodinase, resp. However, examples of even spectroscopic observation of Sec-SeOHs and Sec-SeIs in either protein or small-mol. model systems remain elusive so far, most likely due to their notorious instability. For the synthesis of small-mol. model compds. of these reactive species, it is essential to suppress their very facile bimol. decompn. such as self-condensation and disproportionation. Here we outline a novel method for the synthesis of stable small-mol. model compds. of the selenocysteine-derived reactive species, in which a nano-sized mol. cavity is used as a protective cradle to accommodate the reactive selenocysteine unit. Stabilization by the mol. cradle led to the successful synthesis of Sec-SeOHs, which are stable in soln. at low temps., and a Sec-SeI, which can be isolated as crystals. The catalytic cycle of GPx was investigated using the NMR-observable Sec-SeOH models, and all the chem. processes proposed for the catalytic cycle of GPx, including the bypass process from Sec-SeOH to the corresponding cyclic selenenyl amide, were exptl. confirmed. Detailed protocols for the syntheses of selenopeptide derivs. bearing the mol. cradle and for the spectroscopic monitoring of their reactions are provided.
    21. 21
      Masuda, R.; Kuwano, S.; Sase, S.; Bortoli, M.; Madabeni, A.; Orian, L.; Goto, K. Model Study on the Catalytic Cycle of Glutathione Peroxidase Utilizing Selenocysteine-Containing Tripeptides: Elucidation of the Protective Bypass Mechanism Involving Selenocysteine Selenenic Acids. Bull. Chem. Soc. Jpn. 2022, 95, 1360– 1379,  DOI: 10.1246/bcsj.20220156
      21
      Model study on the catalytic cycle of glutathione peroxidase utilizing selenocysteine-containing tripeptides: Elucidation of the protective bypass mechanism involving selenocysteine selenenic acids
      Masuda, Ryosuke; Kuwano, Satoru; Sase, Shohei; Bortoli, Marco; Madabeni, Andrea; Orian, Laura; Goto, Kei
      Bulletin of the Chemical Society of Japan (2022), 95 (9), 1360-1379CODEN: BCSJA8; ISSN:0009-2673. (Chemical Society of Japan)
      Although much attention has been paid to chem. elucidation of the catalytic cycle of glutathione peroxidase (GPx), it has been hampered by instability of selenocysteine selenenic acid (Sec-SeOH) intermediates. In this study, not only chem. processes of the canonical catalytic cycle but also those involved in the bypass mechanism, including the intramol. cyclization of a Sec-SeOH to the corresponding five-membered ring selenenyl amide were demonstrated exptl. by utilizing selenopeptide model systems in which reactive intermediates can be stabilized by a nano-sized mol. cradle. The resulting cyclic selenenyl amide exhibited higher durability under oxidative conditions than in the state of a Sec-SeOH, corroborating its role as the protective form of GPx. The cyclization of Sec-SeOHs of the Sec-Gly-Thr and Sec-Gly-Lys models, which mimic the catalytic site of isoenzymes GPx1 and GPx4, resp., was found to proceed at lower temp. than in the Sec-Gly-Gly model, which corresponds to the generalized form of the tripeptides in the catalytic site of GPx. The role of the hydrogen-bond accepting moieties in the cyclization process was elucidated by DFT calcn. It was indicated that, if the selenocysteine centers are incorporated in appropriate microenvironments, the bypass mechanism can function efficiently.
    22. 22
      (a) Sase, S.; Kimura, R.; Masuda, R.; Goto, K. Model Study on Trapping of Protein Selenenic Acids by Utilizing a Stable Synthetic Congener. New J. Chem. 2019, 43, 6830– 6833,  DOI: 10.1039/C9NJ01072F
      22a
      Model study on trapping of protein selenenic acids by utilizing a stable synthetic congener
      Sase, Shohei; Kimura, Ryutaro; Masuda, Ryosuke; Goto, Kei
      New Journal of Chemistry (2019), 43 (18), 6830-6833CODEN: NJCHE5; ISSN:1144-0546. (Royal Society of Chemistry)
      A stable primary-alkyl-substituted selenenic acid was developed as a synthetic model of selenocysteine-derived selenenic acid (Sec-SeOH) by taking advantage of a huge cavity-shaped substituent. The primary-alkyl model compd. was successfully applied to model studies on the trapping reaction of protein Sec-SeOH generated in the active site of selenoenzymes with several reagents.
      (b) Sano, T.; Masuda, R.; Sase, S.; Goto, K. Isolable Small-Molecule Cysteine Sulfenic Acid. Chem. Commun. 2021, 57, 2479– 2482,  DOI: 10.1039/D0CC08422K
      22b
      Isolable small-molecule cysteine sulfenic acid
      Sano, Tsukasa; Masuda, Ryosuke; Sase, Shohei; Goto, Kei
      Chemical Communications (Cambridge, United Kingdom) (2021), 57 (20), 2479-2482CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
      An isolable small-mol. cysteine sulfenic acid (Cys-SOH) protected by a mol. cradle was synthesized by direct oxidn. of the corresponding cysteine thiol and its structure was established by X-ray crystallog. anal. Studies on biol. relevant reactivity indicated its usefulness as a biorepresentative small-mol. sulfenic acid model.
    23. 23
      Masuda, R.; Kuwano, S.; Goto, K. Late-Stage Functionalization of the Periphery of Oligophenylene Dendrimers with Various Arene Units via Fourfold C–H Borylation. J. Org. Chem. 2021, 86, 14433– 14443,  DOI: 10.1021/acs.joc.1c01252
      23
      Late-Stage Functionalization of the Periphery of Oligophenylene Dendrimers with Various Arene Units via Fourfold C-H Borylation
      Masuda, Ryosuke; Kuwano, Satoru; Goto, Kei
      Journal of Organic Chemistry (2021), 86 (21), 14433-14443CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
      Late-stage functionalization of the periphery of oligophenylene dendrimers was efficiently achieved via site-selective C-H activation of a preconstructed, readily accessible dendron. By fourfold iridium-catalyzed C-H borylation followed by Suzuki-Miyaura cross-coupling, various arene units were introduced into the end points of the 1,3,5-phenylene-based hydrocarbon dendron. Coupling of the modified dendrons with a core unit, such as 2,6-dibromobenzoic acid derivs., afforded the periphery-functionalized dendrimers that also have an endohedral functionality at the core position.
    24. 24
      Selenocystine 3 was synthesized by the condensation of the acid chloride of DB-Bpsc-OH (ref ) with a selenocystine derivative (Scheme S3), which was prepared according to the following report:Stocking, E. M.; Schwarz, J. N.; Senn, H.; Salzmann, M.; Silks, L. A. Synthesis of L-Selenocystine, L-[77Se] Selenocystine and L-Tellurocystine. J. Chem. Soc., Perkin Trans. 1997, 1, 2443– 2448,  DOI: 10.1039/a600180g
      There is no corresponding record for this reference.
    25. 25
      Goto, K.; Sonoda, D.; Shimada, K.; Sase, S.; Kawashima, T. Modeling of the 5′-Deiodination of Thyroxine by Iodothyronine Deiodinase: Chemical Corroboration of a Selenenyl Iodide Intermediate. Angew. Chem., Int. Ed. 2010, 49, 545– 547,  DOI: 10.1002/anie.200905796
      25
      Modeling of the 5'-Deiodination of Thyroxine by Iodothyronine Deiodinase: Chemical Corroboration of a Selenenyl Iodide Intermediate
      Goto, Kei; Sonoda, Daiju; Shimada, Keiichi; Sase, Shohei; Kawashima, Takayuki
      Angewandte Chemie, International Edition (2010), 49 (3), 545-547, S545/1-S545/6CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Herein, we report exptl. evidence for the formation of a selenenyl iodide in 5'-deiodination of a thyroxine deriv. by an organoselenol, through the use of a nanosized mol. cavity to stabilize the selenenyl iodide intermediate.
    26. 26

      Details of the optimization of the reaction conditions are given in the SI (Scheme S7). We have previously reported that Se-nitrosation of an aromatic selenol to a Se-nitrososelenol was sufficiently fast in CDCl3. However, in the case of Sec–SeH 2b, its Se-nitrosation was slower under similar conditions; for details, see the SI (Figure S5).

      There is no corresponding record for this reference.
    27. 27

      In addition, there was also a very weak absorption at ∼640 nm, which was assigned to the π–π* transition on the basis of our previous DFT calculations on PhSeNO (711 nm); for details, see ref (14).

      There is no corresponding record for this reference.
    28. 28

      The observed absorption maximum of Sec–SeNO 2b is in good agreement with those of our previously reported Se-nitrososelenols; for details, see the SI (Table S4).

      There is no corresponding record for this reference.
    29. 29

      Determined by 1H NMR spectroscopy; we propose that diselenide 6b was formed during the concentration of the reaction mixture containing Sec–SeNO 2b.

      There is no corresponding record for this reference.
    30. 30
      Walter, R.; Roy, J. Selenomethionine, a Potential Catalytic Antioxidant in Biological Systems. J. Org. Chem. 1971, 36, 2561– 2563,  DOI: 10.1021/jo00816a045
      30
      Selenomethionine, a potential catalytic antioxidant in biological systems
      Walter, Roderich; Roy, Jyotirmoy
      Journal of Organic Chemistry (1971), 36 (17), 2561-3CODEN: JOCEAH; ISSN:0022-3263.
      Z = CO2CH2Ph in this abstr. N-Carbobenzoxy-DL-selenomethionine diphenylmethyl ester (I) is treated with NaIO4 or dil. H2O2 to give the selenoxide, MeSe(O)CH2CH2CH(NHZ)CO2CHPh2, which slowly loses O to give I. N-Carbobenzoxydehydroalanine, not the resp. selenoxides, are obtained from the selenocysteine deriv. and the selenocystine deriv., Ph2CHSeCH2CH(NHZ)CO2CHPh2 and Ph2CHO2CCH(NHZ)CH2SeSeCH2(NHZ)CO2ChPh2.
    31. 31
      Ma, S.; Caprioli, R. M.; Hill, K. E.; Burk, R. F. Loss of Selenium from Selenoproteins: Conversion of Selenocysteine to Dehydroalanine in Vitro. J. Am. Soc. Mass Spectrom. 2003, 14, 593– 600,  DOI: 10.1016/S1044-0305(03)00141-7
      31
      Loss of selenium from selenoproteins: conversion of selenocysteine to dehydroalanine in vitro
      Ma, Shuguang; Caprioli, Richard M.; Hill, Kristina E.; Burk, Raymond F.
      Journal of the American Society for Mass Spectrometry (2003), 14 (6), 593-600CODEN: JAMSEF; ISSN:1044-0305. (Elsevier Science Inc.)
      Characterization of reduced and alkylated rat selenoprotein P by mass spectrometry yielded selenopeptides from which one or more selenium atoms were missing. Predicted selenopeptide mass peaks were accompanied by peaks corresponding to the conversion of one or more selenocysteine residues to dehydroalanine(s). Expts. were carried out to det. whether this loss of selenium occurred in vitro. A selenopeptide was isolated that contained two selenocysteine residues that were both in selenide-sulfide linkages with cysteine residues. After the peptide had been reduced and alkylated, in addn. to the predicted mass peak with both selenocysteine residues present, two mass peaks were detected at positions expected for conversion of one and two selenocysteine residues of this selenopeptide to dehydroalanine residues, which was confirmed by tandem mass spectrometry. Similar findings were obtained from a study of another selenoprotein, rat plasma glutathione peroxidase. These results indicate that selenium atoms are lost from selenoproteins during purifn. and characterization. The loss of selenium from selenoproteins is probably through the mechanism of oxidn. of selenocysteine residue to selenoxide followed by syn-β-elimination of selenenic acid during sample processing.
    32. 32
      Orian, L.; Mauri, P.; Roveri, A.; Toppo, S.; Benazzi, L.; Bosello-Travain, V.; De Palma, A.; Maiorino, M.; Miotto, G.; Zaccarin, M.; Polimeno, A.; Flohé, L.; Ursini, F. Selenocysteine Oxidation in Glutathione Peroxidase Catalysis: An MS-Supported Quantum Mechanics Study. Free Radic. Biol. Med. 2015, 87, 1– 14,  DOI: 10.1016/j.freeradbiomed.2015.06.011
      32
      Selenocysteine oxidation in glutathione peroxidase catalysis: an MS-supported quantum mechanics study
      Orian, Laura; Mauri, Pierluigi; Roveri, Antonella; Toppo, Stefano; Benazzi, Louise; Bosello-Travain, Valentina; De Palma, Antonella; Maiorino, Matilde; Miotto, Giovanni; Zaccarin, Mattia; Polimeno, Antonino; Flohe, Leopold; Ursini, Fulvio
      Free Radical Biology & Medicine (2015), 87 (), 1-14CODEN: FRBMEH; ISSN:0891-5849. (Elsevier B.V.)
      Glutathione peroxidases (GPxs) are enzymes working with either selenium or sulfur catalysis. They adopted diverse functions ranging from detoxification of H2O2 to redox signaling and differentiation. The relative stability of the selenoenzymes, however, remained enigmatic in view of the postulated involvement of a highly unstable selenenic acid form during catalysis. Nevertheless, d. functional theory calcns. obtained with a representative active site model verify the mechanistic concept of GPx catalysis and underscore its efficiency. However, they also allow that the selenenic acid, in the absence of the reducing substrate, reacts with a nitrogen in the active site. MS/MS anal. of oxidized rat GPx4 complies with the predicted structure, an 8-membered ring, in which selenium is bound as selenenylamide to the protein backbone. The intermediate can be re-integrated into the canonical GPx cycle by glutathione, whereas, under denaturing conditions, its selenium moiety undergoes β-cleavage with formation of a dehydro-alanine residue. The selenenylamide bypass prevents destruction of the redox center due to over-oxidn. of the selenium or its elimination and likely allows fine-tuning of GPx activity or alternate substrate reactions for regulatory purposes.
    33. 33
      (a) Reich, H. J.; Jasperse, C. P. Organoselenium Chemistry. Redox Chemistry of Selenocysteine Model Systems. J. Am. Chem. Soc. 1987, 109, 5549– 5551,  DOI: 10.1021/ja00252a055
      33a
      Organoselenium chemistry. Redox chemistry of selenocysteine model systems
      Reich, Hans J.; Jasperse, Craig P.
      Journal of the American Chemical Society (1987), 109 (18), 5549-51CODEN: JACSAT; ISSN:0002-7863.
      Two model systems for the selenocysteine active site of the selenoenzyme glutathione peroxidase have been prepd., and their redox chem. was studied. The 1st is 2,2-dimethyl-3-selenopropionic acid and the 2nd is N-acetyl-N'-methyl-α-methylselenocysteamide. Selenides PhCOCMe2SeCH2CRMeCONHMe (R = Me, NHAc) were oxidized by O3 to give selenenic acids HOSeCH2CRMeCONHMe, which underwent in situ cyclization to give cyclic selenamides I [R = Me (II), NHAc]. In aq. McCN, II was in equil. with diselenide (SeCH2CMe2CONHMe)2 (III) and cyclic seleninamide IV. Such equil. are usually completely on the side of the disproportionation products. The reactions of II and IV with PhCH2SH and Me3CSH were studied. The reaction of IV with PhCH2SH gave sequentially PhCH2SSe(O)CH2CMe2CONHMe, II, PhCH2SSeCH2CMe2CONHMe, and finally HSeCH2CMe2CONHMe (V), following closely the proposed mechanism for the redn. steps in the glutathione peroxidase catalytic cycle. Oxidn. of V with either tert-Bu hydroperoxide or m-chloroperbenzoic acid gave in sequence III, II, and IV.
      (b) Sarma, B. K.; Mugesh, G. Glutathione Peroxidase (GPx)-like Antioxidant Activity of the Organoselenium Drug Ebselen: Un-expected Complications with Thiol Exchange Reactions. J. Am. Chem. Soc. 2005, 127, 11477– 11485,  DOI: 10.1021/ja052794t
      33b
      Glutathione Peroxidase (GPx)-like Antioxidant Activity of the Organoselenium Drug Ebselen: Unexpected Complications with Thiol Exchange Reactions
      Sarma, Bani Kanta; Mugesh, G.
      Journal of the American Chemical Society (2005), 127 (32), 11477-11485CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      The factors that are responsible for the relatively low glutathione peroxidase (GPx)-like antioxidant activity of organoselenium compds. such as ebselen (1, 2-phenyl-1,2-benzisoselenazol-3(2H)-one) in the redn. of hydroperoxides with arom. thiols such as benzenethiol and 4-methylbenzenethiol as cosubstrates are described. Exptl. and theor. investigations reveal that the relatively poor GPx-like catalytic activity of organoselenium compds. is due to the undesired thiol exchange reactions that take place at the selenium center in the selenyl sulfide intermediate. This study suggests that any substituent that is capable of enhancing the nucleophilic attack of thiol at sulfur in the selenyl sulfide state would enhance the antioxidant potency of organoselenium compds. such as ebselen. It is proved that the use of thiol having an intramolecularly coordinating group would enhance the biol. activity of ebselen and other organoselenium compds. The presence of strong S···N or S···O interactions in the selenyl sulfide state can modulate the attack of an incoming nucleophile (thiol) at the sulfur atom of the -Se-S- bridge and enhance the GPx activity by reducing the barrier for the formation of the active species selenol.
      (c) Bhowmick, D.; Srivastava, S.; D’Silva, P.; Mugesh, G. Highly Efficient Glutathione Peroxidase and Peroxiredoxin Mimetics Protect Mammalian Cells against Oxidative Damage. Angew. Chem., Int. Ed. 2015, 54, 8449– 8453,  DOI: 10.1002/anie.201502430
      33c
      Highly Efficient Glutathione Peroxidase and Peroxiredoxin Mimetics Protect Mammalian Cells against Oxidative Damage
      Bhowmick, Debasish; Srivastava, Shubhi; D'Silva, Patrick; Mugesh, Govindasamy
      Angewandte Chemie, International Edition (2015), 54 (29), 8449-8453CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Novel isoselenazoles with high glutathione peroxidase (GPx) and peroxiredoxin (Prx) activities provide remarkable cytoprotection to human cells, mainly by exhibiting antioxidant activities in the presence of cellular thiols. The cytotoxicity of the isoselenazoles is found to be significantly lower than that of ebselen, which is being clin. evaluated by several groups for the treatment of reperfusion injuries and stroke, hearing loss, and bipolar disorder. The compds. reported in this paper have the potential to be used as therapeutic agents for disorders mediated by reactive oxygen species.
    34. 34

      These samples were prepared by a procedure similar to that in Scheme 2a.

      There is no corresponding record for this reference.
    35. 35
      (a) Field, L.; Dilts, R. V.; Ravichandran, R.; Lenhert, P. G.; Carnahan, G. E. An Unusually Stable Thionitrite from N-Acetyl-D,L-Penicillamine; X-Ray Crystal and Molecular Structure of 2-(Acetylamino)-2-Carboxy-l,l-Dimethylethyl Thionitrite. J. Chem. Soc. Chem. Commun. 1978, 249– 250,  DOI: 10.1039/c39780000249
      35a
      An unusually stable thionitrite from N-acetyl-D,L-penicillamine; x-ray crystal and molecular structure of 2-(acetylamino)-2-carboxy-1,1-dimethylethyl thionitrite
      Field, Lamar; Dilts, Robert V.; Ravichandran, Ramanathan; Lenhert, P. Galen; Carnahan, Gary E.
      Journal of the Chemical Society, Chemical Communications (1978), (6), 249-50CODEN: JCCCAT; ISSN:0022-4936.
      The structure of HO2CCH(NHAc)C(SR)Me2 (I; R = NO), prepd. (63%) from N-acetyl-DL-penicillamine (I; R = H) by reaction with HNO2, was detd. by x-ray anal. Refluxing of I (R = NO) in MeOH gave 100% [HO2CCH(NHAc)CMe2S]2. The homolytic and heterolytic reactions of I (R = NO) are described.
      (b) Yi, J.; Khan, M. A.; Lee, J.; Richter-Addo, G. B. The Solid-State Molecular Structure of the S-Nitroso Derivative of L-Cysteine Ethyl Ester Hydrochloride. Nitric Oxide 2005, 12, 261– 266,  DOI: 10.1016/j.niox.2005.03.005
      35b
      The solid-state molecular structure of the S-nitroso derivative of L-cysteine ethyl ester hydrochloride
      Yi, Jun; Khan, Masood A.; Lee, Jonghyuk; Richter-Addo, George B.
      Nitric Oxide (2005), 12 (4), 261-266CODEN: NIOXF5; ISSN:1089-8603. (Elsevier)
      Nitrosation of protein sulfhydryl groups to form thionitrites (S-nitrosothiols) has been reported to be important in the biochem. of nitric oxide. Such S-nitrosation of protein thiol residues has been shown to alter the function of some proteins. In this brief communication, we report the x-ray crystal structure of S-nitroso-L-cysteine Et ester hydrochloride. Two rotamers with respect to the N-C-C-S moiety are present in the crystal: the major rotamer is in the gauche + conformation, and the minor rotamer is in the rare anti (trans, antiperiplanar) conformation for a cysteinyl compd. Importantly, the C-S-N=O groups for both rotamers are in the syn (cis, synperiplanar) form. To the best of our knowledge, this is the first reported high-resoln. solid-state structure of an S-nitroso deriv. of a cysteine or cysteinyl-contg. compd.
    36. 36
      (a) Bartberger, M. D.; Houk, K. N.; Powell, S. C.; Mannion, J. D.; Lo, K. Y.; Stamler, J. S.; Toone, E. J. Theory, Spectroscopy, and Crystallographic Analysis of S-Nitrosothiols: Conformational Distribution Dictates Spectroscopic Behavior. J. Am. Chem. Soc. 2000, 122, 5889– 5890,  DOI: 10.1021/ja994476y
      36a
      Theory, Spectroscopy, and Crystallographic Analysis of S-Nitrosothiols: Conformational Distribution Dictates Spectroscopic Behavior
      Bartberger, Michael D.; Houk, K. N.; Powell, Steven C.; Mannion, Joseph D.; Lo, Kenneth Y.; Stamler, Jonathan S.; Toone, Eric J.
      Journal of the American Chemical Society (2000), 122 (24), 5889-5890CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Exptl. (anti/syn ratios, 15N NMR chem. shift, and UV) and theor. [DFT, MP2, and QCISD(T) calcns. of optimized structures and anti/syn ratios and free energy differences, and GIAO calcn. of NMR chem. shifts] results establish the conformations of S-nitrosothiols. Revision of crystallog. structures and structure activity relations are warranted.
      (b) Zhao, Y.-L.; McCarren, P. R.; Houk, K. N.; Choi, B. Y.; Toone, E. J. Nitrosonium-Catalyzed Decomposition of S-Nitrosothiols in Solution: A Theoretical and Experimental Study. J. Am. Chem. Soc. 2005, 127, 10917– 10924,  DOI: 10.1021/ja050018f
      36b
      Nitrosonium-Catalyzed Decomposition of S-Nitrosothiols in Solution: A Theoretical and Experimental Study
      Zhao, Yi-Lei; McCarren, Patrick R.; Houk, K. N.; Choi, Bo Yoon; Toone, Eric J.
      Journal of the American Chemical Society (2005), 127 (31), 10917-10924CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      The decompn. of S-nitrosothiols (RSNO) in soln. under oxidative conditions is significantly faster than can be accounted for by homolysis of the S-N bond. Here we propose a cationic chain mechanism in which nitrosation of nitrosothiol produces a nitrosated cation that, in turn, reacts with a second nitrosothiol to produce nitrosated disulfide and the NO dimer. The nitrosated disulfide acts as a source of nitrosonium for nitrosothiol nitrosation, completing the catalytic cycle. The mechanism accounts for several unexplained facets of nitrosothiol chem. in soln., including the observation that the decompn. of an RSNO is accelerated by O2, mixts. of O2 and NO, and other oxidants, that decompn. is inhibited by thiols and other antioxidants, that decompn. is dependent on sulfur substitution, and that decompn. often shows nonintegral kinetic orders.
    37. 37
      Cha, W.; Meyerhoff, M. E. Catalytic Generation of Nitric Oxide from S-Nitrosothiols Using Immobilized Organoselenium Species. Biomaterials 2007, 28, 19– 27,  DOI: 10.1016/j.biomaterials.2006.08.019
      37
      Catalytic generation of nitric oxide from S-nitrosothiols using immobilized organoselenium species
      Cha Wansik; Meyerhoff Mark E
      Biomaterials (2007), 28 (1), 19-27 ISSN:0142-9612.
      Novel nitric oxide (NO) generating polymeric materials possessing immobilized organoselenium species are described. These materials mimic the capability of small organoselenium molecules as well as a known selenium-containing enzyme, glutathione peroxidase (GPx), by catalytically decomposing S-nitrosothiols (RSNO) into NO and the corresponding free thiol. Model polymeric materials, e.g., cellulose filter paper and polyethylenimine, are modified with an appropriate diselenide species covalently linked to the polymeric structures. Such organoselenium (RSe)-derivatized polymers are shown to generate NO from RSNO species in the presence of an appropriate thiol reducing agent (e.g., glutathione). The likely involvement of both immobilized selenol/selenolate and diselenide species for NO production is suggested via a catalytic pathway, as deduced in separate homogeneous solution phase experiments using non-immobilized forms of small organodiselenide species. Preliminary experiments with the new RSe-polymers clearly demonstrate the ability of such materials to generate NO from RSNO species even after the contact with fresh animal plasma. It is anticipated that such NO generation from endogenous S-nitrosothiols in blood could render RSe-containing polymeric materials more thromboresistant when in contact with flowing blood, owing to NO's ability to inhibit platelet adhesion and activation.
    38. 38
      Kunwar, A.; Priyadarsini, K. I.; Jain, V. K. 3,3′-Diselenodipropionic Acid (DSePA): A Redox Active Multifunctional Molecule of Biological Relevance. Biochim. Biophys. Acta Gen. Subj. 2021, 1865, 129768,  DOI: 10.1016/j.bbagen.2020.129768
      38
      3,3'-Diselenodipropionic acid (DSePA): A redox active multifunctional molecule of biological relevance
      Kunwar, A.; Priyadarsini, K. Indira; Jain, Vimal K.
      Biochimica et Biophysica Acta, General Subjects (2021), 1865 (1), 129768CODEN: BBGSB3; ISSN:0304-4165. (Elsevier B.V.)
      A review. Extensive research is being carried out globally to design and develop new selenium compds. for various biol. applications such as antioxidants, radio-protectors, anti-carcinogenic agents, biocides, etc. In this pursuit, 3,3'-diselenodipropionic acid (DSePA), a synthetic organoselenium compd., has received considerable attention for its biol. activities. This review intends to give a comprehensive account of research on DSePA so as to facilitate further research activities on this organoselenium compd. and to realize its full potential in different areas of biol. and pharmacol. sciences. It is an interesting diselenide structurally related to selenocystine. It shows moderate glutathione peroxidase (GPx)-like activity and is an excellent scavenger of reactive oxygen species (ROS). Exposure to radiation, as envisaged during radiation therapy, has been assocd. with normal tissue side effects and also with the decrease in selenium levels in the body. In vitro and in vivo evaluation of DSePA has confirmed its ability to reduce radiation induced side effects into normal tissues. Administration of DSePA through i.p. (IP) or oral route to mice in a dose range of 2 to 2.5 mg/kg body wt. has shown survival advantage against whole body irradn. and a significant protection to lung tissue against thoracic irradn. Pharmacokinetic profiling of DSePA suggests its max. absorption in the lung. Research work on DSePA reported in fifteen years or so indicates that it is a promising multifunctional organoselenium compd. exhibiting many important activities of biol. relevance apart from radioprotection.
    39. 39
      Yang, Z.; Yang, Y.; Xiong, K.; Li, X.; Qi, P.; Tu, Q.; Jing, F.; Weng, Y.; Wang, J.; Huang, N. Nitric Oxide Producing Coating Mimicking Endothelium Function for Multifunctional Vascular Stents. Biomaterials 2015, 63, 80– 92,  DOI: 10.1016/j.biomaterials.2015.06.016
      39
      Nitric oxide producing coating mimicking endothelium function for multifunctional vascular stents
      Yang, Zhilu; Yang, Ying; Xiong, Kaiqin; Li, Xiangyang; Qi, Pengkai; Tu, Qiufen; Jing, Fengjuan; Weng, Yajun; Wang, Jin; Huang, Nan
      Biomaterials (2015), 63 (), 80-92CODEN: BIMADU; ISSN:0142-9612. (Elsevier Ltd.)
      The continuous release of nitric oxide (NO) by the native endothelium of blood vessels plays a substantial role in the cardiovascular physiol., as it influences important pathways of cardiovascular homeostasis, inhibits vascular smooth muscle cell (VSMC) proliferation, inhibits platelet activation and aggregation, and prevents atherosclerosis. In this study, a NO-catalytic bioactive coating that mimics this endothelium functionality was presented as a hemocompatible coating with potential to improve the biocompatibility of vascular stents. The NO-catalytic bioactive coating was obtained by covalent conjugation of 3,3-diselenodipropionic acid (SeDPA) with glutathione peroxidase (GPx)-like catalytic activity to generate NO from S-nitrosothiols (RSNOs) via specific catalytic reaction. The SeDPA was immobilized to an amine bearing plasma polymd. allylamine (PPAam) surface (SeDPA-PPAam). It showed long-term and continuous ability to catalytically decomp. endogenous RSNO and generate NO. The generated NO remarkably increased the cGMP synthesis both in platelets and human umbilical artery smooth muscle cells (HUASMCs). The surface exhibited a remarkable suppression of collagen-induced platelet activation and aggregation. It suppressed the adhesion, proliferation and migration of HUASMCs. Addnl., it was found that the NO catalytic surface significantly enhanced human umbilical vein endothelial cell (HUVEC) adhesion, proliferation and migration. The in vivo results indicated that the NO catalytic surface created a favorable microenvironment of competitive growth of HUVECs over HUASMCs for promoting re-endothelialization and reducing restenosis of stents in vivo.
    40. 40
      Höfler, L.; Meyerhoff, M. E. Modeling the Effect of Oxygen on the Amperometric Response of Immobilized Organoselenium-Based S-Nitrosothiol Sensors. Anal. Chem. 2011, 83, 619– 624,  DOI: 10.1021/ac1021979
      40
      Modeling the Effect of Oxygen on the Amperometric Response of Immobilized Organoselenium-Based S-Nitrosothiol Sensors
      Hofler, Lajos; Meyerhoff, Mark E.
      Analytical Chemistry (Washington, DC, United States) (2011), 83 (2), 619-624CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      Amperometric detection of S-nitrosothiols (RSNOs) at submicromolar levels in blood samples is of potential importance for monitoring endothelial function and other disease states that involve changes in physiol. nitric oxide (NO) prodn. It is shown here that the elimination of dissolved oxygen from samples is crit. when covalently attached diselenocystamine-based amperometric RSNO sensors are used for practical RSNO measurements. The newest generation of RSNO sensors utilizes an amperometric NO gas sensor with a thin organoselenium modified dialysis membrane mounted at the distal sensing tip. Sample RSNOs are catalytically reduced to NO within the dialysis membrane by the immobilized organoselenium species. In the presence of oxygen, the sensitivity of these sensors for measuring low levels of RSNOs (<μM) is greatly reduced. It is demonstrated that the main scavenger of the generated nitric oxide is not the dissolved oxygen but rather superoxide anion radical generated from the reaction of the reduced organoselenium species (the reactive species in the catalytic redox cycle) and dissolved oxygen. Computer simulations of the response of the RSNO sensor using rate consts. and diffusion coeffs. for the reactions involved, known from the literature or estd. from fitting to the obsd. amperometric response curves, as well as the specific geometric dimensions of the RSNO sensor, further support that nitric oxide and superoxide anion radical quickly react resulting in near zero sensor sensitivity toward RSNO concns. in the submicromolar concn. range. Elimination of oxygen from samples helps improve sensor detection limits to ∼10 nM levels of RSNOs.
    41. 41
      Cha, W.; Meyerhoff, M. E. Catalytic Generation of Nitric Oxide from S-Nitrosothiols Using Immobilized Organoselenium Species. Biomaterials 2007, 28, 19– 27,  DOI: 10.1016/j.biomaterials.2006.08.019
      41
      Catalytic generation of nitric oxide from S-nitrosothiols using immobilized organoselenium species
      Cha Wansik; Meyerhoff Mark E
      Biomaterials (2007), 28 (1), 19-27 ISSN:0142-9612.
      Novel nitric oxide (NO) generating polymeric materials possessing immobilized organoselenium species are described. These materials mimic the capability of small organoselenium molecules as well as a known selenium-containing enzyme, glutathione peroxidase (GPx), by catalytically decomposing S-nitrosothiols (RSNO) into NO and the corresponding free thiol. Model polymeric materials, e.g., cellulose filter paper and polyethylenimine, are modified with an appropriate diselenide species covalently linked to the polymeric structures. Such organoselenium (RSe)-derivatized polymers are shown to generate NO from RSNO species in the presence of an appropriate thiol reducing agent (e.g., glutathione). The likely involvement of both immobilized selenol/selenolate and diselenide species for NO production is suggested via a catalytic pathway, as deduced in separate homogeneous solution phase experiments using non-immobilized forms of small organodiselenide species. Preliminary experiments with the new RSe-polymers clearly demonstrate the ability of such materials to generate NO from RSNO species even after the contact with fresh animal plasma. It is anticipated that such NO generation from endogenous S-nitrosothiols in blood could render RSe-containing polymeric materials more thromboresistant when in contact with flowing blood, owing to NO's ability to inhibit platelet adhesion and activation.
    42. 42

      We previously reported the generation of BpqSeNO by transnitrosation from S-nitrosoglutathione (GSNO) (ref (14)). It was also confirmed that treatment of 4b with GSNO afforded 2b in conversion yield of ca. 30% (Scheme S12).

      There is no corresponding record for this reference.

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