Essential Insight of Direct Electron Transfer-Type Bioelectrocatalysis by Membrane-Bound d-Fructose Dehydrogenase with Structural Bioelectrochemistry

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Cryo-EM structures were deposited in the Protein Data Bank for rFDH-R (PDB ID: 8JEJ), rFDH-O (PDB ID: 8JEK) and rFDH-D (PDB ID: 7W2J and 7WSQ).

This article references 79 other publications.

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   The possibility of producing elec. power from chem. energy with biol. catalysts has induced the development of biofuel cells as viable energy sources for powering portable and implanted electronic devices. These power sources employ biocatalysts, called enzymes, which are highly specific and catalytic towards the oxidn. of a biofuel and the redn. of oxygen or hydrogen peroxide. Enzymes, on one hand, are promising candidates to replace expensive noble metal-based catalysts in fuel cell research. On the other hand, they offer the exciting prospect of a new generation of fuel cells which harvest energy from body fluids. Biofuel cells which use glucose as a fuel are particularly interesting for generating electricity to power electronic devices inside a living body. Hydrogen consuming biofuel cells represent an emerging alternative to platinum catalysts due to comparable efficiencies and the capability to operate at lower temps. Currently, these technologies are not competitive with existing commercialised fuel cell devices due to limitations including insufficient power outputs and lifetimes. The advantages and challenges facing glucose biofuel cells for implantation and hydrogen biofuel cells will be summarised along with recent promising advances and the future prospects of these exotic energy-harvesting devices.

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   A review. Catalytic four-electron redn. of O2 to water is one of the most extensively studied electrochem. reactions due to O2 exceptional availability and high O2/H2O redox potential, which may in particular allow highly energetic reactions in fuel cells. To circumvent the use of expensive and inefficient Pt catalysts, multicopper oxidases (MCOs) have been envisioned because they provide efficient O2 redn. with almost no overpotential. MCOs have been used to elaborate enzymic biofuel cells (EBFCs), a subclass of fuel cells in which enzymes replace the conventional catalysts. A glucose/O2 EBFC, with a glucose oxidizing anode and a O2 reducing MCO cathode, could become the in vivo source of electricity that would power sometimes in the future integrated medical devices. This review covers the challenges and advances in the electrochem. of MCOs and their use in EBFCs with a particular emphasis on the last 6 years. First basic features of MCOs and EBFCs are presented. Clues provided by electrochem. to understand these enzymes and how they behave once connected at electrodes are described. Progresses realized in the development of efficient biocathodes for O2 redn. relying both on direct and mediated electron transfer mechanism are then discussed. Some implementations in EBFCs are finally presented.

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   Chemical Reviews (Washington, DC, United States) (2019), 119 (16), 9509-9558CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)

   A review. The ever-increasing demands for clean and sustainable energy sources combined with rapid advances in biointegrated portable or implantable electronic devices have stimulated intensive research activities in enzymic (bio)fuel cells (EFCs). The use of renewable biocatalysts, the utilization of abundant green, safe, and high energy d. fuels, together with the capability of working at modest and biocompatible conditions make EFCs promising as next generation alternative power sources. However, the main challenges (low energy d., relatively low power d., poor operational stability, and limited voltage output) hinder future applications of EFCs. This review aims at exploring the underlying mechanism of EFCs and providing possible practical strategies, methodologies and insights to tackle these issues. First, this review summarizes approaches in achieving high energy densities in EFCs, particularly, employing enzyme cascades for the deep/complete oxidn. of fuels. Second, strategies for increasing power densities in EFCs, including increasing enzyme activities, facilitating electron transfers, employing nanomaterials, and designing more efficient enzyme-electrode interfaces, are described. The potential of EFCs/(super)capacitor combination is discussed. Third, the review evaluates a range of strategies for improving the stability of EFCs, including the use of different enzyme immobilization approaches, tuning enzyme properties, designing protective matrixes, and using microbial surface displaying enzymes. Fourthly, approaches for the improvement of the cell voltage of EFCs are highlighted. Finally, future developments and a prospective on EFCs are envisioned.

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   A review. Bioelectrocatalysis is an interdisciplinary research field combining biocatalysis and electrocatalysis via the utilization of materials derived from biol. systems as catalysts to catalyze the redox reactions occurring at an electrode. Bioelectrocatalysis synergistically couples the merits of both biocatalysis and electrocatalysis. The advantages of biocatalysis include high activity, high selectivity, wide substrate scope, and mild reaction conditions. The advantages of electrocatalysis include the possible utilization of renewable electricity as an electron source and high energy conversion efficiency. These properties are integrated to achieve selective biosensing, efficient energy conversion, and the prodn. of diverse products. This review seeks to systematically and comprehensively detail the fundamentals, analyze the existing problems, summarize the development status and applications, and look toward the future development directions of bioelectrocatalysis. First, the structure, function, and modification of bioelectrocatalysts are discussed. Second, the essentials of bioelectrocatalytic systems, including electron transfer mechanisms, electrode materials, and reaction medium, are described. Third, the application of bioelectrocatalysis in the fields of biosensors, fuel cells, solar cells, catalytic mechanism studies, and bioelectrosyntheses of high-value chems. are systematically summarized. Finally, future developments and a perspective on bioelectrocatalysis are suggested.

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    A review. The role of the electrode material in the efficiency of direct (non-mediated) bioelectrocatalytic redn. of H2O2 catalyzed by horseradish peroxidase (HRP) is studied and discussed. The variations in direct peroxidase bioelectrocatalysis when coming from carbon/graphite to metal electrodes and oxides, as well as modified electrodes, are analyzed regarding the variations in adsorption/orientation of peroxidase at the electrodes, interfacial electron transfer rates and mechanism of catalysis.

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    A review on the use of dynamic electrochem. to study the mechanism of redox enzymes, with exclusive emphasis on the configuration where the protein is adsorbed onto an electrode and electron transfer is direct.

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    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXotlOnur0%253D&md5=2a4cf491ec7471796f9eca75cd11d178
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    Falk, M.; Blum, Z.; Shleev, S. Direct Electron Transfer Based Enzymatic Fuel Cells. Electrochim. Acta 2012, 82, 191– 202,  DOI: 10.1016/j.electacta.2011.12.133

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    Direct electron transfer based enzymatic fuel cells

    Falk, Magnus; Blum, Zoltan; Shleev, Sergey

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    A review of some historical developments made in the field of enzymic fuel cells, discussing important design considerations taken when constructing mediator-, cofactor-, and membrane-less biol. fuel cells. Since the topic is rather extensive, only biol. fuel cells utilizing direct electron transfer reactions on both the anodic and cathodic sides are considered. Moreover, the performance of mostly glucose/oxygen biodevices is analyzed and compared. We also present some unpublished results on mediator-, cofactor-, and membrane-less glucose/oxygen biol. fuel cells recently designed in our group and tested in different human physiol. fluids, such as blood, plasma, saliva, and tears. Finally, further perspectives for biol. fuel cell applications are highlighted.

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    Principles of direct (mediator free) bioelectrocatalysis

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    A review. Current mini-review is devoted to principles and focuses on the most important trends of bioelectrocatalysis, i.e. acceleration of electrochem. reactions with the use of biol. catalysts. The history of direct bioelectrocatalysis, starting from electrochem. of redox enzymes is presented. The direct bioelectrocatalysis presumes the direct electron exchange (tunneling) between the enzyme active site and the electrode without any redox mediators. Special attention is paid to the novel approach: enzyme orientation during immobilization to improve efficiency of bioelectrocatalysis. Using this particular approach the limiting performance characteristics of the enzymes in bioelectrocatalysis are achieved. The phenomenon of the direct bioelectrocatalysis by intact cells is discussed.

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18. 18

    Sarauli, D.; Xu, C.; Dietzel, B.; Schulz, B.; Lisdat, F. A Multilayered Sulfonated Polyaniline Network with Entrapped Pyrroloquinoline Quinone-Dependent Glucose Dehydrogenase: Tunable Direct Bioelectrocatalysis. J. Mater. Chem. B 2014, 2 (21), 3196– 3203,  DOI: 10.1039/C4TB00336E

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    A multilayered sulfonated polyaniline network with entrapped pyrroloquinoline quinone-dependent glucose dehydrogenase: tunable direct bioelectrocatalysis

    Sarauli, David; Xu, Chenggang; Dietzel, Birgit; Schulz, Burkhard; Lisdat, Fred

    Journal of Materials Chemistry B: Materials for Biology and Medicine (2014), 2 (21), 3196-3203CODEN: JMCBDV; ISSN:2050-7518. (Royal Society of Chemistry)

    A feasible approach to construct multilayer films of sulfonated polyanilines - PMSA1 and PABMSA1 - contg. different ratios of aniline, 2-methoxyaniline-5-sulfonic acid (MAS) and 3-aminobenzoic acid (AB), with the entrapped redox enzyme pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH) on Au and ITO electrode surfaces, is described. The formation of layers has been followed and confirmed by electrochem. impedance spectroscopy (EIS), which demonstrates that the multilayer assembly can be achieved in a progressive and uniform manner. The gold and ITO electrodes subsequently modified with PMSA1:PQQ-GDH and PABMSA1 films are studied by cyclic voltammetry (CV) and UV-Vis spectroscopy which show a significant direct bioelectrocatalytical response to the oxidn. of the substrate glucose without any addnl. mediator. This response correlates linearly with the no. of deposited layers. Furthermore, the constructed polymer/enzyme multilayer system exhibits a rather good long-term stability, since the catalytic current response is maintained for more than 60% of the initial value even after two weeks of storage. This verifies that a productive interaction of the enzyme embedded in the film of substituted polyaniline can be used as a basis for the construction of bioelectronic units, which are useful as indicators for processes liberating glucose and allowing optical and electrochem. transduction.

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    Milton, R. D.; Minteer, S. D. Direct Enzymatic Bioelectrocatalysis: Differentiating between Myth and Reality. J. R. Soc. Interface 2017, 14 (131), 20170253,  DOI: 10.1098/rsif.2017.0253

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    Direct enzymatic bioelectrocatalysis: differentiating between myth and reality

    Milton, Ross D.; Minteer, Shelley D.

    Journal of the Royal Society, Interface (2017), 14 (131), 20170253/1-20170253/13CODEN: JRSICU; ISSN:1742-5662. (Royal Society)

    Enzymic bioelectrocatalysis is being increasingly exploited to better understand oxidoreductase enzymes, to develop minimalistic yet specific biosensor platforms, and to develop alternative energy conversion devices and bioelectrosynthetic devices for the prodn. of energy and/or important chem. commodities. In some cases, these enzymes are able to electronically communicate with an appropriately designed electrode surface without the requirement of an electron mediator to shuttle electrons between the enzyme and electrode. This phenomenon has been termed direct electron transfer or direct bioelectrocatalysis. While many thorough studies have extensively investigated this fascinating feat, it is sometimes difficult to differentiate desirable enzymic bioelectrocatalysis from electrocatalysis deriving from inactivated enzyme that may have also released its catalytic cofactor. This article will review direct bioelectrocatalysis of several oxidoreductases, with an emphasis on expts. that provide support for direct bioelectrocatalysis vs. denatured enzyme or dissocd. cofactor. Finally, this review will conclude with a series of proposed control expts. that could be adopted to discern successful direct electronic communication of an enzyme from its denatured counterpart.

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    Jenner, L. P.; Butt, J. N. Electrochemistry of Surface-Confined Enzymes: Inspiration, Insight and Opportunity for Sustainable Biotechnology. Curr. Opin. Electrochem. 2018, 8, 81– 88,  DOI: 10.1016/j.coelec.2018.03.021

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    Electrochemistry of surface-confined enzymes: Inspiration, insight and opportunity for sustainable biotechnology

    Jenner, Leon P.; Butt, Julea N.

    Current Opinion in Electrochemistry (2018), 8 (), 81-88CODEN: COEUCY; ISSN:2451-9111. (Elsevier B.V.)

    A review. Redox enzymes can generate electricity from sunlight and produce valuable chems., including fuels, from low-value materials. When an electrode takes the role of an enzyme's natural redox partner, these properties inspire creative approaches to generate renewable resources. Enzymic fuel cells produce electricity, enzyme electrosynthesis drives chem. transformations and biophotovoltaics harness solar energy. Underpinning rational development of these applications, time-dependent currents resolved by dynamic electrochem. provide quant. insight into the determinants of enzyme activity. This article reviews popular and emerging routes to sequester, study and exploit redox enzymes on two- and three-dimensional electrode materials. Studies are highlighted that draw on synergies of these different aspects of enzyme electrochem.

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    Yates, N. D. J.; Fascione, M. A.; Parkin, A. Methodologies for “Wiring” Redox Proteins/Enzymes to Electrode Surfaces. Chem. - A Eur. J. 2018, 24 (47), 12164– 12182,  DOI: 10.1002/chem.201800750

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    Methodologies for "Wiring" Redox Proteins/Enzymes to Electrode Surfaces

    Yates, Nicholas D. J.; Fascione, Martin A.; Parkin, Alison

    Chemistry - A European Journal (2018), 24 (47), 12164-12182CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)

    A review. The immobilization of redox proteins or enzymes onto conductive surfaces has application in the anal. of biol. processes, the fabrication of biosensors, and in the development of green technologies and biochem. synthetic approaches. This review evaluates the methods through which redox proteins can be attached to electrode surfaces in a "wired" configuration, i.e., one that facilitates direct electron transfer. The feasibility of simple electroactive adsorption onto a range of electrode surfaces is illustrated, with a highlight on the recent advances that have been achieved in biotechnol. device construction using carbon materials and metal oxides. The covalent crosslinking strategies commonly used for the modification and biofunctionalization of electrode surfaces are also evaluated. Recent innovations in harnessing chem. biol. methods for elec. wiring redox biol. to surfaces are emphasized.

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    Bollella, P.; Gorton, L.; Antiochia, R. Direct Electron Transfer of Dehydrogenases for Development of 3rd Generation Biosensors and Enzymatic Fuel Cells. Sensors (Switzerland) 2018, 18 (5), 1319,  DOI: 10.3390/s18051319

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23. 23

    Evans, R. M.; Siritanaratkul, B.; Megarity, C. F.; Pandey, K.; Esterle, T. F.; Badiani, S.; Armstrong, F. A. The Value of Enzymes in Solar Fuels Research-Efficient Electrocatalysts through Evolution. Chem. Soc. Rev. 2019, 48 (7), 2039– 2052,  DOI: 10.1039/C8CS00546J

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    The value of enzymes in solar fuels research - efficient electrocatalysts through evolution

    Evans, Rhiannon M.; Siritanaratkul, Bhavin; Megarity, Clare F.; Pandey, Kavita; Esterle, Thomas F.; Badiani, Selina; Armstrong, Fraser A.

    Chemical Society Reviews (2019), 48 (7), 2039-2052CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)

    The reasons for using enzymes as tools for solar fuels research are discussed. Many oxidoreductases, including components of membrane-bound electron-transfer chains in living organisms, are extremely active when directly attached to an electrode, at which they display their inherent catalytic activity as elec. current. Electrocatalytic voltammograms, which show the rate of electron flow at steady-state, provide direct information on enzyme efficiency with regard to optimizing use of available energy, a factor that would have driven early evolution. Oxidoreductases have evolved to minimise energy wastage ('overpotential requirement') across electron-transport chains where rate and power must be maximised for a given change in Gibbs energy, in order to perform work such as proton pumping. At the elementary level (uncoupled from work output), redox catalysis by many enzymes operates close to the thermodynamically reversible limit. Examples include efficient and selective electrocatalytic redn. of CO2 to CO or formate - reactions that are very challenging at the chem. level, yet appear almost reversible when catalyzed by enzymes. Expts. also reveal the fleeting existence of reversible four-electron O2 redn. and water oxidn. by 'blue' Cu oxidases, another reaction of great importance in realizing a future based on renewable energy. Being aware that such enzymes have evolved to approach perfection, chemists are interested to know the minimal active site structure they would need to synthesize in order to mimic their performance.

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24. 24

    Mazurenko, I.; Hitaishi, V. P.; Lojou, E. Recent Advances in Surface Chemistry of Electrodes to Promote Direct Enzymatic Bioelectrocatalysis. Curr. Opin. Electrochem. 2020, 19, 113– 121,  DOI: 10.1016/j.coelec.2019.11.004

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    24

    Recent advances in surface chemistry of electrodes to promote direct enzymatic bioelectrocatalysis

    Mazurenko, Ievgen; Hitaishi, Vivek Pratap; Lojou, Elisabeth

    Current Opinion in Electrochemistry (2020), 19 (), 113-121CODEN: COEUCY; ISSN:2451-9111. (Elsevier B.V.)

    Redox enzymes catalyze major reactions in microorganisms to supply energy for life. Their use in electrochem. biodevices requires their integration on electrodes, while maintaining their activity and optimizing their stability. In return, such applicative development puts forward the knowledge on involved catalytic mechanisms, providing a direct electrode connection of the enzyme is fulfilled. Enzymes being large mols. with active site embedded in an insulating moiety, direct bioelectrocatalysis supposes strategies for specific orientation of the enzyme to be developed. In this review, we summarize recent advances during the past 3 years in the chem. modification of electrodes favoring direct electrocatalysis. We present the different methodologies used according to the electrode materials, including metals, carbon-based electrodes, or porous structures and discuss the gained insights into bioelectrocatalysis. We esp. focus on enzyme engineering, which appears as an emerging strategy for enzyme anchoring. Remaining challenges will be discussed with regard to these later findings.

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25. 25

    Smutok, O.; Kavetskyy, T.; Katz, E. Recent Trends in Enzyme Engineering Aiming to Improve Bioelectrocatalysis Proceeding with Direct Electron Transfer. Curr. Opin. Electrochem. 2022, 31, 100856,  DOI: 10.1016/j.coelec.2021.100856

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    25

    Recent trends in enzyme engineering aiming to improve bioelectrocatalysis proceeding with direct electron transfer

    Smutok, Oleh; Kavetskyy, Taras; Katz, Evgeny

    Current Opinion in Electrochemistry (2022), 31 (), 100856CODEN: COEUCY; ISSN:2451-9111. (Elsevier B.V.)

    Among the known types of electrochem. biosensors, the third generation based on the ability of some enzymes to direct electron transfer (DET) is the most promising one. The enzyme property to DET is depending on its capability to electron transfer from enzymically reduced built-in native cofactor (FMN, FAD, pyrroloquinoline quinone, or heme) to a conductive surface directly for single cofactor enzymes or through a native structural electron acceptor (heme or copper-contg. prosthetic groups) for multicofactor enzymes. Thus, there are two possibilities to use such type enzymes: to find a natural source of the enzyme with these properties; or to construct the recombinant chimeric analogs using the gene-engineering techniques. The modern mol. genetics opens the possibility to be independent of million-year natural evolution and engineer the specific enzymes for scientific and technol. needs. This brief review is focused mostly on the recent publications on application of DET-capable engineered enzymes for the third-generation electrochem. biosensors.

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    Heller, A. Electrical Wiring of Redox Enzymes. Acc. Chem. Res. 1990, 23 (5), 128– 134,  DOI: 10.1021/ar00173a002

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    Electrical wiring of redox enzymes

    Heller, Adam

    Accounts of Chemical Research (1990), 23 (5), 128-34CODEN: ACHRE4; ISSN:0001-4842.

    A review with 82 refs, of redox enzymes in which the functional electron transfer center, normally surrounded by an insulating protein matrix, can be elec. connected to an external source of current through a path of fast electron-relaying redox couples. Such wiring is achieved through electrostatically or covalently binding to the enzyme-proteins, high-mol.-wt. redox polycations having segments anchored to electrodes. With the wired enzymes, subsecond response time amperometric biosensors can be built.

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27. 27

    Gao, W.; Emaminejad, S.; Nyein, H. Y. Y.; Challa, S.; Chen, K.; Peck, A.; Fahad, H. M.; Ota, H.; Shiraki, H.; Kiriya, D.; Lien, D. H.; Brooks, G. A.; Davis, R. W.; Javey, A. Fully Integrated Wearable Sensor Arrays for Multiplexed in situ Perspiration Analysis. Nature 2016, 529 (7587), 509– 514,  DOI: 10.1038/nature16521

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    Fully integrated wearable sensor arrays for multiplexed in situ perspiration analysis

    Gao, Wei; Emaminejad, Sam; Nyein, Hnin Yin Yin; Challa, Samyuktha; Chen, Kevin; Peck, Austin; Fahad, Hossain M.; Ota, Hiroki; Shiraki, Hiroshi; Kiriya, Daisuke; Lien, Der-Hsien; Brooks, George A.; Davis, Ronald W.; Javey, Ali

    Nature (London, United Kingdom) (2016), 529 (7587), 509-514CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)

    Wearable sensor technologies are essential to the realization of personalized medicine through continuously monitoring an individual's state of health. Sampling human sweat, which is rich in physiol. information, could enable non-invasive monitoring. Previously reported sweat-based and other non-invasive biosensors either can only monitor a single analyte at a time or lack on-site signal processing circuitry and sensor calibration mechanisms for accurate anal. of the physiol. state. Given the complexity of sweat secretion, simultaneous and multiplexed screening of target biomarkers is crit. and requires full system integration to ensure the accuracy of measurements. Here we present a mech. flexible and fully integrated (i.e., no external anal. is needed) sensor array for multiplexed in situ perspiration anal., which simultaneously and selectively measures sweat metabolites (such as glucose and lactate) and electrolytes (such as sodium and potassium ions), as well as the skin temp. (to calibrate the response of the sensors). Our work bridges the technol. gap between signal transduction, conditioning (amplification and filtering), processing and wireless transmission in wearable biosensors by merging plastic-based sensors that interface with the skin with silicon integrated circuits consolidated on a flexible circuit board for complex signal processing. This application could not have been realized using either of these technologies alone owing to their resp. inherent limitations. The wearable system is used to measure the detailed sweat profile of human subjects engaged in prolonged indoor and outdoor phys. activities, and to make a real-time assessment of the physiol. state of the subjects. This platform enables a wide range of personalized diagnostic and physiol. monitoring applications.

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28. 28

    Bruen, D.; Delaney, C.; Florea, L.; Diamond, D. Glucose Sensing for Diabetes Monitoring: Recent Developments. Sensors (Switzerland) 2017, 17 (8), 1866,  DOI: 10.3390/s17081866

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    Teymourian, H.; Barfidokht, A.; Wang, J. Electrochemical Glucose Sensors in Diabetes Management: An Updated Review (2010–2020). Chem. Soc. Rev. 2020, 49 (21), 7671– 7709,  DOI: 10.1039/D0CS00304B

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    Electrochemical glucose sensors in diabetes management: an updated review (2010-2020)

    Teymourian, Hazhir; Barfidokht, Abbas; Wang, Joseph

    Chemical Society Reviews (2020), 49 (21), 7671-7709CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)

    A review. While over half a century has passed since the introduction of enzyme glucose biosensors by Clark and Lyons, this important field has continued to be the focus of immense research activity. Extensive efforts during the past decade have led to major scientific and technol. innovations towards tight monitoring of diabetes. Such continued progress toward advanced continuous glucose monitoring platforms, either minimal- or non-invasive, holds considerable promise for addressing the limitations of finger-prick blood testing toward tracking glucose trends over time, optimal therapeutic interventions, and improving the life of diabetes patients. However, despite these major developments, the field of glucose biosensors is still facing major challenges. The scope of this review is to present the key scientific and technol. advances in electrochem. glucose biosensing over the past decade (2010-present), along with current obstacles and prospects towards the ultimate goal of highly stable and reliable real-time minimally-invasive or non-invasive glucose monitoring. After an introduction to electrochem. glucose biosensors, we highlight recent progress based on using advanced nanomaterials at the electrode-enzyme interface of three generations of glucose sensors. Subsequently, we cover recent activity and challenges towards next-generation wearable non-invasive glucose monitoring devices based on innovative sensing principles, alternative body fluids, advanced flexible materials, and novel platforms. This is followed by highlighting the latest progress in the field of minimally-invasive continuous glucose monitoring (CGM) which offers real-time information about interstitial glucose levels, by focusing on the challenges toward developing biocompatible membrane coatings to protect electrochem. glucose sensors against surface biofouling. Subsequent sections cover new anal. concepts of self-powered glucose sensors, paper-based glucose sensing and multiplexed detection of diabetes-related biomarkers. Finally, we will cover the latest advances in com. available devices along with the upcoming future technologies.

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30. 30

    Datta, S.; Mori, Y.; Takagi, K.; Kawaguchi, K.; Chen, Z. W.; Okajima, T.; Kuroda, S.; Ikeda, T.; Kano, K.; Tanizawa, K.; Mathews, F. S. Structure of a Quinohemoprotein Amine Dehydrogenase with an Uncommon Redox Cofactor and Highly Unusual Crosslinking. Proc. Natl. Acad. Sci. U.S.A. 2001, 98 (25), 14268– 14273,  DOI: 10.1073/pnas.241429098

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    Structure of a quinohemoprotein amine dehydrogenase with an uncommon redox cofactor and highly unusual crosslinking

    Datta, Saumen; Mori, Youichi; Takagi, Kazuyoshi; Kawaguchi, Katsunori; Chen, Zhi-Wei; Okajima, Toshihide; Kuroda, Shun'ichi; Ikeda, Tokuji; Kano, Kenji; Tanizawa, Katsuyuki; Mathews, F. Scott

    Proceedings of the National Academy of Sciences of the United States of America (2001), 98 (25), 14268-14273CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)

    The crystal structure of the heterotrimeric quinohemoprotein amine dehydrogenase from Paracoccus denitrificans has been detd. at 2.05-Å resoln. Within an 82-residue subunit is contained an unusual redox cofactor, cysteine tryptophylquinone (CTQ), consisting of an orthoquinone-modified tryptophan side chain covalently linked to a nearby cysteine side chain. The subunit is surrounded on three sides by a 489-residue, four-domain subunit that includes a diheme cytochrome c. Both subunits sit on the surface of a third subunit, a 337-residue seven-bladed β-propeller that forms part of the enzyme active site. The small catalytic subunit is internally crosslinked by three highly unusual covalent cysteine to aspartic or glutamic acid thioether linkages in addn. to the cofactor crossbridge. The catalytic function of the enzyme as well as the biosynthesis of the unusual catalytic subunit is discussed.

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31. 31

    Liu, J.; Chakraborty, S.; Hosseinzadeh, P.; Yu, Y.; Tian, S.; Petrik, I.; Bhagi, A.; Lu, Y. Metalloproteins Containing Cytochrome, Iron-Sulfur, or Copper Redox Centers. Chem. Rev. 2014, 114 (8), 4366– 4369,  DOI: 10.1021/cr400479b

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    Metalloproteins containing cytochrome, iron-sulfur, or copper redox centers

    Liu, Jing; Chakraborty, Saumen; Hosseinzadeh, Parisa; Yu, Yang; Tian, Shiliang; Petrik, Igor; Bhagi, Ambika; Lu, Yi

    Chemical Reviews (Washington, DC, United States) (2014), 114 (8), 4366-4469CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)

    A review. The authors summarize 3 important classes of redox centers involved electron transfer (ET) processes. Although each class spans a wide range of redn. potentials, none of them can cover the whole range needed for biol. purposes. Together, however, they can cover the whole range, with cytochromes in the middle, Fe-S centers toward the lower end, and cupredoxins toward the higher end. All 3 redox centers have structural features that make them unique, and yet they also show many similarities that make them excellent choices for ET processes. Here, the authors examine structural features that are responsible for their redox properties, including knowledge gained from recent progress in fine-tuning the redox centers.

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32. 32

    Takeda, K.; Nakamura, N. Direct Electron Transfer Process of Pyrroloquinoline Quinone-Dependent and Flavin Adenine Dinucleotide-Dependent Dehydrogenases: Fundamentals and Applications. Curr. Opin. Electrochem. 2021, 29, 100747,  DOI: 10.1016/j.coelec.2021.100747

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    Direct electron transfer process of pyrroloquinoline quinone-dependent and flavin adenine dinucleotide-dependent dehydrogenases: Fundamentals and applications

    Takeda, Kouta; Nakamura, Nobuhumi

    Current Opinion in Electrochemistry (2021), 29 (), 100747CODEN: COEUCY; ISSN:2451-9111. (Elsevier B.V.)

    A Review Pyrroloquinoline quinone-dependent and FAD-dependent enzymes catalyze the oxidn. of various compds. These enzymes are large mols., and the embedding of active sites in the insulating portion of the mol. generally make direct bioelectrocatalysis difficult. Dehydrogenases with a built-in electron transfer domain are capable of direct electron transfer (DET) to an electrode. Attempts have also been made to realize DET by artificially producing fusion proteins in which protein engineering is fully exploited to connect electron transfer domains. Furthermore, the reports of the DET of enzymes without an electron transfer domain to an electrode have started to appear. This review summarizes recent reports on fundamental findings on DET and applications using DET-enzyme electrodes.

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33. 33

    Ikeda, T.; Kobayashi, D.; Matsushita, F.; Sagara, T.; Niki, K. Bioelectrocatalysis at Electrodes Coated with Alcohol Dehydrogenase, a Quinohemoprotein with Heme c Serving as a Built-in Mediator. J. Electroanal. Chem. 1993, 361 (1–2), 221– 228,  DOI: 10.1016/0022-0728(93)87058-4

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    Bioelectrocatalysis at electrodes coated with alcohol dehydrogenase, a quinohemoprotein with heme c serving as a built-in mediator

    Ikeda, Tokuji; Kobayashi, Daisuke; Matsushita, Fumio; Sagara, Takamasa; Niki, Katsumi

    Journal of Electroanalytical Chemistry (1993), 361 (1-2), 221-8CODEN: JECHES ISSN:.

    Alc. dehydrogenase (ADH), a bacterial membrane-bound protein contg. pyrroloquinoline quinone (PQQ) and heme c was held by adsorption on electrodes of gold, silver, glassy carbon, or pyrolytic graphite. All the electrodes with adsorbed ADH produced anodic currents which oxidized ethanol, in which the adsorbed ADH catalyzed the electrolysis of ethanol. The electrocatalysis behavior could be described by a theor. equation for bioelectrocatalysis at an enzyme-coated electrode, and was characterized by two quantities, the Michaelis const. Km, and max. c.d. Imax/A. Using electroreflectance measurements with an ADH-coated gold electrode it was revealed that electron transfer occurred between heme c of the adsorbed ADH and the electrode. On the basis of these results, the reaction mechanism of the bioelectrocatalysis is discussed and oriented adsorption of ADH is proposed with the heme c moiety being in close contact with the electrode and with the PQQ moiety, the site reacting with the substrate, facing toward the soln.

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34. 34

    Adachi, T.; Kitazumi, Y.; Shirai, O.; Kano, K. Direct Electron Transfer-Type Bioelectrocatalysis by Membrane-Bound Aldehyde Dehydrogenase from Gluconobacter Oxydans and Cyanide Effects on its Bioelectrocatalytic Properties. Electrochem. Commun. 2021, 123, 106911,  DOI: 10.1016/j.elecom.2020.106911

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    34

    Direct electron transfer-type bioelectrocatalysis by membrane-bound aldehyde dehydrogenase from Gluconobacter oxydans and cyanide effects on its bioelectrocatalytic properties

    Adachi, Taiki; Kitazumi, Yuki; Shirai, Osamu; Kano, Kenji

    Electrochemistry Communications (2021), 123 (), 106911CODEN: ECCMF9; ISSN:1388-2481. (Elsevier B.V.)

    The bioelectrocatalytic properties of membrane-bound aldehyde dehydrogenase (AlDH) from Gluconobacter oxydans NBRC12528 were evaluated. AlDH exhibited direct electron transfer (DET)-type bioelectrocatalytic activity for acetaldehyde oxidn. at several kinds of electrodes. The kinetic and thermodn. parameters for bioelectrocatalytic acetaldehyde oxidn. were estd. based on the partially random orientation model. Moreover, at the multi-walled carbon nanotube-modified electrode, the coordination of CN- to AlDH switched the direction of the DET-type bioelectrocatalysis to acetate redn. under acidic conditions. These phenomena were discussed from a thermodn. viewpoint.

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    Treu, B. L.; Arechederra, R.; Minteer, S. D. Bioelectrocatalysis of Ethanol via PQQ-Dependent Dehydrogenases Utilizing Carbon Nanomaterial Supports. J. Nanosci. Nanotechnol. 2009, 9 (4), 2374– 2380,  DOI: 10.1166/jnn.2009.SE33

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    35

    Bioelectrocatalysis of ethanol via PQQ-dependent dehydrogenases utilizing carbon nanomaterial supports

    Treu, Becky L.; Arechederra, Robert; Minteer, Shelley D.

    Journal of Nanoscience and Nanotechnology (2009), 9 (4), 2374-2380CODEN: JNNOAR; ISSN:1533-4880. (American Scientific Publishers)

    In bioelectrocatalysis, nanomaterials are typically used as a conductive bridge for the gap between the site of oxidn./redn. (i.e., enzymic biocatalyst) and the current collector (electrode). In this paper, carbon nanomaterial supports have been employed in conjunction with heme-c contg. pyrroloquinoline quinone-dependent alc. dehydrogenase (PQQ-ADH) and aldehyde dehydrogenase (PQQ-AldDH) oxidoreductase enzymes as oxidn. catalysts to produce stable high surface area catalyst supports for the bioelectrocatalysis of ethanol in biofuel cells. The structure of PQQ-ADH and PQQ-AldDH allow for direct electron transfer (DET) between the enzymes and carbon nanomaterial support without the use of addnl. charge carrying chem. mediators. In this paper, the employment of nanomaterials are used to produce stable, high surface area catalyst supports which aid in enzyme adsorption and direct electron transfer. Fundamental DET studies were performed on both PQQ-ADH and PQQ-AldDH in order to understand the processes occurring at the electrode surface. Data shows a direct correlation between concn. of substrate and peak potential and peak current. Incorporating nanotubes into this technol. has allowed an increase in the c.d. of ethanol/air biofuel cells by up to 14.5 fold and increased the power d. by up to 18.0 fold.

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    Kakehi, N.; Yamazaki, T.; Tsugawa, W.; Sode, K. A Novel Wireless Glucose Sensor Employing Direct Electron Transfer Principle Based Enzyme Fuel Cell. Biosens. Bioelectron. 2007, 22 (9–10), 2250– 2255,  DOI: 10.1016/j.bios.2006.11.004

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    36

    A novel wireless glucose sensor employing direct electron transfer principle based enzyme fuel cell

    Kakehi, Noriko; Yamazaki, Tomohiko; Tsugawa, Wakako; Sode, Koji

    Biosensors & Bioelectronics (2007), 22 (9-10), 2250-2255CODEN: BBIOE4; ISSN:0956-5663. (Elsevier B.V.)

    In this paper we present a novel wireless glucose biosensing system employing direct electron transfer principle based enzyme fuel cell. Using the glucose dehydrogenase complex, which is composed of a catalytic subunit contg. FAD, the cytochrome c subunit that harbors heme c as the electron transfer subunit, and chaperone-like subunit, a direct electron transfer-type glucose enzyme fuel cell was constructed. The enzyme glucose fuel cell generated elec. power, and the open-circuit voltage showed glucose concn. dependence, which suggests potential applications for this glucose-sensing system. We constructed a miniaturized "all-in-one" glucose enzyme fuel cell, which represents a compartmentless fuel that is based on the direct electron transfer principle. This involved the combination of a wireless transmitter system and a simple and miniaturized continuous glucose monitoring system, which operated continuously for about 3 days with stable response. This is the first demonstration of an enzyme-based direct electron transfer-type enzyme fuel cell and fuel cell-type glucose sensor which can be utilized as a s.c. implantable system for continuous glucose monitoring.

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37. 37

    Ikeda, T.; Matsushita, F.; Senda, M. Amperometric Fructose Sensor Based on Direct Bioelectrocatalysis. Biosens. Bioelectron. 1991, 6 (4), 299– 304,  DOI: 10.1016/0956-5663(91)85015-O

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    Amperometric fructose sensor based on direct bioelectrocatalysis

    Ikeda, Tokuji; Matsushita, Fumio; Senda, Mitsugi

    Biosensors & Bioelectronics (1991), 6 (4), 299-304CODEN: BBIOE4; ISSN:0956-5663.

    Fructose dehydrogenase (EC 1.1.99.11) from bacterial membranes was immobilized on a C-paste electrode by covering the enzyme layer with a dialysis membrane. The fructose dehydrogenase-modified C-paste electrode showed a current response to D-fructose without the addn. of any external electron transfer mediators. The current response was independent of the O concn. in the soln. Steady-state currents were obtained when measured at fixed electrode potentials. The dependence of the steady-state current on the potential, the pH of the soln. and the temp. was studied. On the basis of this investigations, it was shown that the fructose dehydrogenase-modified C-paste electrode could be used as an unmediated amperometric fructose sensor. D-Fructose in fruits was measured by using the present electrode. A method of eliminating the effect of L-ascorbic acid is also described.

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    Okuda-Shimazaki, J.; Yoshida, H.; Sode, K. FAD Dependent Glucose Dehydrogenases - Discovery and Engineering of Representative Glucose Sensing Enzymes -. Bioelectrochemistry 2020, 132, 107414,  DOI: 10.1016/j.bioelechem.2019.107414

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    FAD dependent glucose dehydrogenases - Discovery and engineering of representative glucose sensing enzymes -

    Okuda-Shimazaki, Junko; Yoshida, Hiromi; Sode, Koji

    Bioelectrochemistry (2020), 132 (), 107414CODEN: BIOEFK; ISSN:1567-5394. (Elsevier B.V.)

    The history of the development of glucose sensors goes hand-in-hand with the history of the discovery and the engineering of glucose-sensing enzymes. Glucose oxidase (GOx) has been used for glucose sensing since the development of the first electrochem. glucose sensor. The principle utilizing oxygen as the electron acceptor is designated as the first-generation electrochem. enzyme sensors. With increasing demand for hand-held and cost-effective devices for the "self-monitoring of blood glucose (SMBG)", second-generation electrochem. sensor strips employing electron mediators have become the most popular platform. To overcome the inherent drawback of GOx, namely, the use of oxygen as the electron acceptor, various glucose dehydrogenases (GDHs) have been utilized in second-generation principle-based sensors. Among the various enzymes employed in glucose sensors, GDHs harboring FAD as the redox cofactor, FADGDHs, esp. those derived from fungi, fFADGDHs, are currently the most popular enzymes in the sensor strips of second-generation SMBG sensors. In addn., the third-generation principle, employing direct electron transfer (DET), is considered the most elegant approach and is ideal for use in electrochem. enzyme sensors. However, glucose oxidoreductases capable of DET are limited. One of the most prominent GDHs capable of DET is a bacteria-derived FADGDH complex (bFADGDH). bFADGDH has three distinct subunits; the FAD harboring the catalytic subunit, the small subunit, and the electron-transfer subunit, which makes bFADGDH capable of DET. In this review, we focused on the two representative glucose sensing enzymes, fFADGDHs and bFADGDHs, by presenting their discovery, sources, and protein and enzyme properties, and the current engineering strategies to improve their potential in sensor applications.

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    Adachi, T.; Kaida, Y.; Kitazumi, Y.; Shirai, O.; Kano, K. Bioelectrocatalytic Performance of D-Fructose Dehydrogenase. Bioelectrochemistry 2019, 129, 1– 9,  DOI: 10.1016/j.bioelechem.2019.04.024

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    Bioelectrocatalytic performance of D-fructose dehydrogenase

    Adachi, Taiki; Kaida, Yuya; Kitazumi, Yuki; Shirai, Osamu; Kano, Kenji

    Bioelectrochemistry (2019), 129 (), 1-9CODEN: BIOEFK; ISSN:1567-5394. (Elsevier B.V.)

    This review summarizes the bioelectrocatalytic properties of D-fructose dehydrogenase (FDH), while taking into consideration its enzymic characteristics. FDH is a membrane-bound flavohemo-protein with a mol. mass of 138 kDa, and it catalyzes the oxidn. of D-fructose to 5-keto-D-fructose. The characteristic feature of FDH is its strong direct-electron-transfer (DET)-type bioelectrocatalytic activity. The pathway of the DET-type reaction is discussed. An overview of the application of FDH-based bioelectrocatalysis to biosensors and biofuel cells is also presented, and the benefits and problems assocd. with it are extensively discussed.

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40. 40

    Yamaoka, H.; Ferri, S.; Sode, M. F. K. Essential Role of the Small Subunit of Thermostable Glucose Dehydrogenase from Burkholderia cepacia. Biotechnol. Lett. 2004, 26 (22), 1757– 1761,  DOI: 10.1007/s10529-004-4582-0

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    40

    Essential role of the small subunit of thermostable glucose dehydrogenase from Burkholderia cepacia

    Yamaoka, Hideaki; Ferri, Stefano; Sode, Masako Fujikawa Koji

    Biotechnology Letters (2004), 26 (22), 1757-1761CODEN: BILED3; ISSN:0141-5492. (Kluwer Academic Publishers)

    The co-expression in Escherichia coli of the γ-subunit and the catalytic α-subunit of the thermostable glucose dehydrogenase (GDH) from Burkholderia cepacia sp. SM4 produced 12.7 U GDH activity mg-1 protein. A 47-amino acid, twin-arginine translocase signal peptide was identified at the amino terminus of the γ-subunit. The expression of the α-subunit in the absence of the γ-subunit or the γ-subunit signal peptide failed to produce any detectable GDH protein or activity. The γ-subunit may be a chaperone-like component that assists folding of the α-subunit polypeptide to the active form and its translocation to the periplasm.

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41. 41

    Yoshida, H.; Kojima, K.; Shiota, M.; Yoshimatsu, K.; Yamazaki, T.; Ferri, S.; Tsugawa, W.; Kamitori, S.; Sode, K. X-Ray Structure of the Direct Electron Transfer-Type FAD Glucose Dehydrogenase Catalytic Subunit Complexed with a Hitchhiker Protein. Acta Crystallogr. Sect. D Struct. Biol. 2019, 75, 841– 851,  DOI: 10.1107/S2059798319010878

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    41

    X-ray structure of the direct electron transfer-type FAD glucose dehydrogenase catalytic subunit complexed with a hitchhiker protein

    Yoshida, Hiromi; Kojima, Katsuhiro; Shiota, Masaki; Yoshimatsu, Keiichi; Yamazaki, Tomohiko; Ferri, Stefano; Tsugawa, Wakako; Kamitori, Shigehiro; Sode, Koji

    Acta Crystallographica, Section D: Structural Biology (2019), 75 (9), 841-851CODEN: ACSDAD; ISSN:2059-7983. (International Union of Crystallography)

    The bacterial FAD (FAD)-dependent glucose dehydrogenase complex derived from Burkholderia cepacia (BcGDH) is a representative mol. of direct electron transfer-type FAD-dependent dehydrogenase complexes. In this study, the X-ray structure of BcGDHγα, the catalytic subunit (α-subunit) of BcGDH complexed with a hitchhiker protein (γ-subunit), was detd. The most prominent feature of this enzyme is the presence of the 3Fe-4S cluster, which is located at the surface of the catalytic subunit and functions in intramol. and intermol. electron transfer from FAD to the electron-transfer subunit. The structure of the complex revealed that these two mols. are connected through disulfide bonds and hydrophobic interactions, and that the formation of disulfide bonds is required to stabilize the catalytic subunit. The structure of the complex revealed the putative position of the electron-transfer subunit. A comparison of the structures of BcGDHγα and membrane-bound fumarate reductases suggested that the whole BcGDH complex, which also includes the membrane-bound β-subunit contg. three heme c moieties, may form a similar overall structure to fumarate reductases, thus accomplishing effective electron transfer.

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42. 42

    Shiota, M.; Yamazaki, T.; Yoshimatsu, K.; Kojima, K.; Tsugawa, W.; Ferri, S.; Sode, K. An Fe-S Cluster in the Conserved Cys-Rich Region in the Catalytic Subunit of FAD-Dependent Dehydrogenase Complexes. Bioelectrochemistry 2016, 112, 178– 183,  DOI: 10.1016/j.bioelechem.2016.01.010

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    42

    An Fe-S cluster in the conserved Cys-rich region in the catalytic subunit of FAD-dependent dehydrogenase complexes

    Shiota, Masaki; Yamazaki, Tomohiko; Yoshimatsu, Keiichi; Kojima, Katsuhiro; Tsugawa, Wakako; Ferri, Stefano; Sode, Koji

    Bioelectrochemistry (2016), 112 (), 178-183CODEN: BIOEFK; ISSN:1567-5394. (Elsevier B.V.)

    Several bacterial FAD-harboring dehydrogenase complexes comprise three distinct subunits: a catalytic subunit with FAD, a cytochrome c subunit contg. three hemes, and a small subunit. Owing to the cytochrome c subunit, these dehydrogenase complexes have the potential to transfer electrons directly to an electrode. Despite various electrochem. applications and engineering studies of FAD-dependent dehydrogenase complexes, the intra/inter-mol. electron transfer pathway has not yet been revealed. In this study, we focused on the conserved Cys-rich region in the catalytic subunits using the catalytic subunit of FAD dependent glucose dehydrogenase complex (FADGDH) as a model, and site-directed mutagenesis and ESR (EPR) were performed. By co-expressing a hitch-hiker protein (γ-subunit) and a catalytic subunit (α-subunit), FADGDH γα complexes were prepd., and the properties of the catalytic subunit of both wild type and mutant FADGDHs were investigated. Substitution of the conserved Cys residues with Ser resulted in the loss of dye-mediated glucose dehydrogenase activity. ICP-AEM and EPR analyses of the wild-type FADGDH catalytic subunit revealed the presence of a 3Fe-4S-type iron-sulfur cluster, whereas none of the Ser-substituted mutants showed the EPR spectrum characteristic for this cluster. The results suggested that three Cys residues in the Cys-rich region constitute an iron-sulfur cluster that may play an important role in the electron transfer from FAD (intra-mol.) to the multi-heme cytochrome c subunit (inter-mol.) electron transfer pathway. These features appear to be conserved in the other three-subunit dehydrogenases having an FAD cofactor.

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43. 43

    Okuda-Shimazaki, J.; Yoshida, H.; Lee, I.; Kojima, K.; Suzuki, N.; Tsugawa, W.; Yamada, M.; Inaka, K.; Tanaka, H.; Sode, K. Microgravity environment grown crystal tructure information based engineering of direct electron transfer type glucose dehydrogenase. Commun. Biol. 2022, 5, 1334,  DOI: 10.1038/s42003-022-04286-9

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    43

    Microgravity environment grown crystal structure information based engineering of direct electron transfer type glucose dehydrogenase

    Okuda-Shimazaki, Junko; Yoshida, Hiromi; Lee, Inyoung; Kojima, Katsuhiro; Suzuki, Nanoha; Tsugawa, Wakako; Yamada, Mitsugu; Inaka, Koji; Tanaka, Hiroaki; Sode, Koji

    Communications Biology (2022), 5 (1), 1334CODEN: CBOIDQ; ISSN:2399-3642. (Nature Portfolio)

    The heterotrimeric FAD dependent glucose dehydrogenase is a promising enzyme for direct electron transfer (DET) principle-based glucose sensors within continuous glucose monitoring systems. We elucidate the structure of the subunit interface of this enzyme by prepg. heterotrimer complex protein crystals grown under a space microgravity environment. Based on the proposed structure, we introduce inter-subunit disulfide bonds between the small and electron transfer subunits (5 pairs), as well as the catalytic and the electron transfer subunits (9 pairs). Without compromising the enzyme's catalytic efficiency, a mutant enzyme harboring Pro205Cys in the catalytic subunit, Asp383Cys and Tyr349Cys in the electron transfer subunit, and Lys155Cys in the small subunit, is detd. to be the most stable of the variants. The developed engineered enzyme demonstrate a higher catalytic activity and DET ability than the wild type. This mutant retains its full activity below 70°C as well as after incubation at 75°C for 15 min - much higher temps. than the current gold std. enzyme, glucose oxidase, is capable of withstanding.

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44. 44

    Ameyama, M.; Shinagawa, E.; Matsushita, K.; Adachi, O. D-Fructose Dehydrogenase of Gluconobacter Industrius: Purification, Characterization, and Application to Enzymatic Microdetermination of D-Fructose. J. Bacteriol. 1981, 145 (2), 814– 823,  DOI: 10.1128/jb.145.2.814-823.1981

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    44

    D-Fructose dehydrogenase of Gluconobacter industrius: purification, characterization, and application to enzymic microdetermination of D-fructose

    Ameyama, Minoru; Shinagawa, Emiko; Matsushita, Kazunobu; Adachi, Osao

    Journal of Bacteriology (1981), 145 (2), 814-23CODEN: JOBAAY; ISSN:0021-9193.

    D-Fructose dehydrogenase (I) was solubilized and purified from the membrane fraction of glycerol-grown G. industrius IFO 3260. Purified I was tightly bound to a c-type cytochrome and another peptide existing as a dehydrogenase-cytochrome complex. I was homogeneous in anal. ultracentrifugation as well as gel filtration. The mol. wt. of the I complex was ∼140,000, and SDS-polyacrylamide gel electrophoresis showed the presence of 3 components having mol. wts. of 67,000 (the enzyme protein), 50,800 (cytochrome c), and 19,700 (unknown function). Only D-fructose was readily oxidized by I in the presence of dyes such as ferricyanide, 2,6-dichlorophenolindophenol, or phenazine methosulfate. The optimum pH of D-fructose oxidn. was 4.0. I was stable at pH 4.5-6.0. Stability of purified I was much enhanced by the presence of detergent in the enzyme soln. Removal of detergent from the enzyme soln. facilitated the aggregation of I and caused its inactivation. An apparent Km for D-fructose was 10-2M with purified I. I was a satisfactory reagent for microdetn. of D-fructose.

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45. 45

    Kawai, S.; Goda-Tsutsumi, M.; Yakushi, T.; Kano, K.; Matsushita, K. Heterologous Overexpression and Characterization of a Flavoprotein-Cytochrome c Complex Fructose Dehydrogenase of Gluconobacter Japonicus NBRC3260. Appl. Environ. Microbiol. 2013, 79 (5), 1654– 1660,  DOI: 10.1128/AEM.03152-12

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    45

    Heterologous overexpression and characterization of a flavoprotein-cytochrome c complex fructose dehydrogenase of Gluconobacter japonicus NBRC3260

    Kawai, Shota; Goda-Tsutsumi, Maiko; Yakushi, Toshiharu; Kano, Kenji; Matsushita, Kazunobu

    Applied and Environmental Microbiology (2013), 79 (5), 1654-1660CODEN: AEMIDF; ISSN:0099-2240. (American Society for Microbiology)

    A heterotrimeric flavoprotein-cytochrome c complex fructose dehydrogenase (FDH) of Gluconobacter japonicus NBRC3260 catalyzes the oxidn. of D-fructose to produce 5-keto-D-fructose and is used for diagnosis and basic research purposes as a direct electron transfer-type bioelectrocatalysis. The fdhSCL genes encoding the FDH complex of G. japonicus NBRC3260 were isolated by a PCR-based gene amplification method with degenerate primers designed from the amino-terminal amino acid sequence of the large subunit and sequenced. Three open reading frames for fdhSCL encoding the small, cytochrome c, and large subunits, resp., were found and were presumably in a polycistronic transcriptional unit. Heterologous overexpression of fdhSCL was conducted using a broad-host-range plasmid vector, pBBR1MCS-4, carrying a DNA fragment contg. the putative promoter region of the membrane-bound alc. dehydrogenase gene of Gluconobacter oxydans and a G. oxydans strain as the expression host. The authors also constructed derivs. modified in the translational initiation codon to ATG from TTG, designated TTGFDH and ATGFDH. Membranes of the cells producing recombinant TTGFDH and ATGFDH showed ∼20 times and 100 times higher specific activity than those of G. japonicus NBRC3260, resp. The cells producing only FdhS and FdhL had no fructose-oxidizing activity, but showed significantly high D-fructose:ferricyanide oxidoreductase activity in the sol. fraction of cell exts., whereas the cells producing the FDH complex showed activity in the membrane fraction. It is reasonable to conclude that the cytochrome c subunit is responsible not only for membrane anchoring but also for ubiquinone redn.

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46. 46

    Kawai, S.; Yakushi, T.; Matsushita, K.; Kitazumi, Y.; Shirai, O.; Kano, K. The Electron Transfer Pathway in Direct Electrochemical Communication of Fructose Dehydrogenase with Electrodes. Electrochem. commun. 2014, 38, 28– 31,  DOI: 10.1016/j.elecom.2013.10.024

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    46

    The electron transfer pathway in direct electrochemical communication of fructose dehydrogenase with electrodes

    Kawai, Shota; Yakushi, Toshiharu; Matsushita, Kazunobu; Kitazumi, Yuki; Shirai, Osamu; Kano, Kenji

    Electrochemistry Communications (2014), 38 (), 28-31CODEN: ECCMF9; ISSN:1388-2481. (Elsevier B.V.)

    A heterotrimeric membrane-bound fructose dehydrogenase (FDH) complex from Gluconobacter japonicus NBRC3260 catalyzes oxidn. of D-fructose into 2-keto-D-fructose and is one of typical enzymes allowing a direct electron transfer (DET)-type bioelectrocatalysis. Subunits I and II have a covalently bound FAD and three heme C moieties, resp. We have constructed subunit I/III subcomplex (ΔcFDH) lacking of the heme C subunit. ΔCFDH catalyzes the oxidn. of D-fructose with several artificial electron acceptors, but loses the DET ability. The formal potentials (E°') of the three heme C moieties of FDH have been detd. to be - 10 ± 4, 60 ± 8 and 150 ± 4 mV (vs. Ag|AgCl|sat. KCl) at pH 5.0, while the onset potential of FDH-catalyzed DET-type bioelectrocatalytic wave is - 100 mV. Judging from these results, we conclude that FDH communicates electrochem. with electrodes via the heme C, and discuss the pathway of the electron transfer in the catalytic process.

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47. 47

    Suzuki, Y.; Sowa, K.; Kitazumi, Y.; Shirai, O. The Redox Potential Measurements for Heme Moieties in Variants of D-Fructose Dehydrogenase Based on Mediator-Assisted Potentiometric Titration. Electrochemistry 2021, 89, 337– 339,  DOI: 10.5796/electrochemistry.21-00044

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    47

    The redox potential measurements for heme moieties in variants of D-fructose dehydrogenase based on mediator-assisted potentiometric titration

    Suzuki, Yohei; Sowa, Keisei; Kitazumi, Yuki; Shirai, Osamu

    Electrochemistry (Tokyo, Japan) (2021), 89 (4), 337-339CODEN: EECTFA; ISSN:2186-2451. (Electrochemical Society of Japan)

    The effect of mutation on the redox potentials (E°') of the heme moieties in the variants of d-fructose dehydrogenase (FDH) was investigated by mediated spectroelectrochem. titrns. The replacement of the axial ligand of heme from methionine to glutamine changes the E°' value more neg. than that of the corresponding heme moiety in the recombinant (native) FDH (rFDH). The detd. E°' values of non-targeted heme moieties in the variants were also shifted in a neg. direction from that in rFDH. Thus, enzyme modification changes E°' of the heme moieties in unmodified protein regions.

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48. 48

    Hibino, Y.; Kawai, S.; Kitazumi, Y.; Shirai, O.; Kano, K. Mutation of Heme c Axial Ligands in D-Fructose Dehydrogenase for Investigation of Electron Transfer Pathways and Reduction of Overpotential in Direct Electron Transfer-Type Bioelectrocatalysis. Electrochem. commun. 2016, 67, 43– 46,  DOI: 10.1016/j.elecom.2016.03.013

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    48

    Mutation of heme c axial ligands in D-fructose dehydrogenase for investigation of electron transfer pathways and reduction of overpotential in direct electron transfer-type bioelectrocatalysis

    Hibino, Yuya; Kawai, Shota; Kitazumi, Yuki; Shirai, Osamu; Kano, Kenji

    Electrochemistry Communications (2016), 67 (), 43-46CODEN: ECCMF9; ISSN:1388-2481. (Elsevier B.V.)

    D-Fructose dehydrogenase (FDH), a flavoprotein-cytochrome c complex, exhibits high activity in direct electron transfer (DET)-type bioelectrocatalysis. One of the three types of heme c in FDH is the electron-donating site to the electrodes, and another heme c is presumed to not be involved in the catalytic cycle. In order to confirm the electron transfer pathway, the authors constructed three mutants in which the sixth axial methionine ligand (M301, M450, or M578) of one of the hemes was replaced with glutamine, which was selected with the expectation that it would shift the formal potential of the hemes in the neg. direction. An M450Q mutant successfully reduced the overpotential by ∼0.2 V, giving a limiting current close to that of the native FDH. In contrast, an M301Q mutant remained almost unchanged and an M578Q mutant drastically decreased DET-type catalytic activity. The electron transfer in the native FDH occurs in sequence from the flavin, through the heme c with M578, to the heme c with M450 (as the electron-donating site to the electrodes), without going through the heme c with M301. The M450Q mutant will be useful for biofuel cells because of the decreased overpotential.

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49. 49

    Hibino, Y.; Kawai, S.; Kitazumi, Y.; Shirai, O.; Kano, K. Construction of a Protein-Engineered Variant of D-Fructose Dehydrogenase for Direct Electron Transfer-Type Bioelectrocatalysis. Electrochem. commun. 2017, 77, 112– 115,  DOI: 10.1016/j.elecom.2017.03.005

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    49

    Construction of a protein-engineered variant of D-fructose dehydrogenase for direct electron transfer-type bioelectrocatalysis

    Hibino, Yuya; Kawai, Shota; Kitazumi, Yuki; Shirai, Osamu; Kano, Kenji

    Electrochemistry Communications (2017), 77 (), 112-115CODEN: ECCMF9; ISSN:1388-2481. (Elsevier B.V.)

    D-Fructose dehydrogenase (FDH), a heterotrimeric membrane-bound enzyme, exhibits strong activity in direct electron transfer- (DET-)type bioelectrocatalysis. We constructed a variant (Δ1cFDH) that lacks 143 amino acid residues involving one heme c moiety (called heme 1c) on the N-terminus of subunit II, and characterized the bioelectrocatalytic properties of Δ1cFDH using cyclic voltammetry. A clear DET-type catalytic oxidn. wave of D-fructose was obsd. at the Δ1cFDH-adsorbed Au electrodes. The result clearly indicates that the electrons accepted at the FAD catalytic center in subunit I are transferred to electrodes via two of the three heme c moieties in subunit II without going through heme 1c. In addn., the limiting c.d. of Δ1cFDH was one and a half times larger than that of the native FDH in DET-type bioelectrocatalysis. The downsizing protein engineering causes an increase in the surface concn. of the electrochem. effective enzymes and an improvement in the heterogeneous electron transfer kinetics.

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50. 50

    Kaida, Y.; Hibino, Y.; Kitazumi, Y.; Shirai, O.; Kano, K. Ultimate Downsizing of D-Fructose Dehydrogenase for Improving the Performance of Direct Electron Transfer-Type Bioelectrocatalysis. Electrochem. Commun. 2019, 98, 101– 105,  DOI: 10.1016/j.elecom.2018.12.001

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    50

    Ultimate downsizing of D-fructose dehydrogenase for improving the performance of direct electron transfer-type bioelectrocatalysis

    Kaida, Yuya; Hibino, Yuya; Kitazumi, Yuki; Shirai, Osamu; Kano, Kenji

    Electrochemistry Communications (2019), 98 (), 101-105CODEN: ECCMF9; ISSN:1388-2481. (Elsevier B.V.)

    D-Fructose dehydrogenase (FDH), a membrane-bound heterotrimeric enzyme, shows strong activity in direct electron transfer (DET)-type bioelectrocatalysis. An FDH variant (Δ1c2cFDH) which lacks 199 amino acid residues including two heme c moieties from N-terminus was constructed, and its DET-type bioelectrocatalytic performance was evaluated with cyclic voltammetry at Au planar electrodes. A DET-type catalytic current of D-fructose oxidn. was clearly obsd. on Δ1c2cFDH-adsorbed Au electrodes. Detailed anal. of the steady-state catalytic current indicated that Δ1c2cFDH transports the electrons to the electrode via heme 3c at a more neg. potential and at more improved kinetics than the recombinant (native) FDH.

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51. 51

    Suzuki, Y.; Makino, F.; Miyata, T.; Tanaka, H.; Namba, K.; Kano, K.; Sowa, K.; Kitazumi, Y.; Shirai, O. Structural and Bioelectrochemical Elucidation of Direct Electron Transfer-Type Membrane-Bound Fructose Dehydrogenase. ChemRxiv 2022,  DOI: 10.26434/chemrxiv-2022-d7hl9

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    Farver, O.; Skov, L. K.; Young, S.; Bonander, N.; Karlsson, B.; Vanngard, T. G.; Pecht, I. Aromatic Residues May Enhance Intramolecular Electron Transfer in Azurin. J. Am. Chem. Soc. 1997, 119 (23), 5453– 5454,  DOI: 10.1021/ja964386i

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    Aromatic Residues May Enhance Intramolecular Electron Transfer in Azurin

    Farver, Ole; Skov, Lars K.; Young, Simon; Bonander, Nicklas; Karlsson, B. Goeran; Vaenngrd, Tore; Pecht, Israel

    Journal of the American Chemical Society (1997), 119 (23), 5453-5454CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    In order to probe the possible influence of arom. residues on electron transfer (ET), we have now produced single site mutated azurins in which Trp48 has been substituted by other amino acids, both arom. and nonarom. residues, and detd. the rate consts. for intramol. ET as a function of temp.

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    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2sXjtlGjtbg%253D&md5=6dfdf934166a592b5c3c80ebff1d2b6b
53. 53

    Shih, C.; Museth, A. K.; Abrahamsson, M.; Blanco-Rodriguez, A. M.; Di Bilio, A. J.; Sudhamsu, J.; Crane, B. R.; Ronayne, K. L.; Towrie, M.; Vlček, A.; Richards, J. H.; Winkler, J. R.; Gray, H. B. Tryptophan-Accelerated Electron Flow through Proteins. Science (80-.). 2008, 320 (5884), 1760– 1762,  DOI: 10.1126/science.1158241

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    Takematsu, K.; Williamson, H.; Blanco-Rodríguez, A. M.; Sokolová, L.; Nikolovski, P.; Kaiser, J. T.; Towrie, M.; Clark, I. P.; Vlček, A.; Winkler, J. R.; Gray, H. B. Tryptophan-Accelerated Electron Flow across a Protein-Protein Interface. J. Am. Chem. Soc. 2013, 135 (41), 15515– 15525,  DOI: 10.1021/ja406830d

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    Tryptophan-Accelerated Electron Flow Across a Protein-Protein Interface

    Takematsu, Kana; Williamson, Heather; Blanco-Rodriguez, Ana Maria; Sokolova, Lucie; Nikolovski, Pavle; Kaiser, Jens T.; Towrie, Michael; Clark, Ian P.; Vlcek, Antonin; Winkler, Jay R.; Gray, Harry B.

    Journal of the American Chemical Society (2013), 135 (41), 15515-15525CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)

    We report a new metallolabeled blue copper protein, Re126W122CuI Pseudomonas aeruginosa azurin, which has three redox sites at well-defined distances in the protein fold: ReI(CO)3(4,7-dimethyl-1,10-phenanthroline) covalently bound at H126, a Cu center, and an indole side chain W122 situated between the Re and Cu sites (Re-W122-(indole) = 13.1 Å, dmp-W122-(indole) = 10.0 Å, Re-Cu = 25.6 Å). Near-UV excitation of the Re chromophore leads to prompt CuI oxidn. (<50 ns), followed by slow back ET to regenerate CuI and ground-state ReI with biexponential kinetics, 220 ns and 6 μs. From spectroscopic measurements of kinetics and relative ET yields at different concns., it is likely that the photoinduced ET reactions occur in protein dimers, (Re126W122CuI)2 and that the forward ET is accelerated by intermol. electron hopping through the interfacial tryptophan: *Re//←W122←CuI, where // denotes a protein-protein interface. Soln. mass spectrometry confirms a broad oligomer distribution with prevalent monomers and dimers, and the crystal structure of the CuII form shows two Re126W122CuII mols. oriented such that redox cofactors Re-(dmp) and W122-indole on different protein mols. are located at the interface at much shorter intermol. distances (Re-W122-(indole) = 6.9 Å, dmp-W122-(indole) = 3.5 Å, and Re-Cu = 14.0 Å) than within single protein folds. Whereas forward ET is accelerated by hopping through W122, BET is retarded by a space jump at the interface that lacks specific interactions or water mols. These findings on interfacial electron hopping in (Re126W122CuI)2 shed new light on optimal redox-unit placements required for functional long-range charge sepn. in protein complexes.

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55. 55

    Takematsu, K.; Williamson, H. R.; Nikolovski, P.; Kaiser, J. T.; Sheng, Y.; Pospíšil, P.; Towrie, M.; Heyda, J.; Hollas, D.; Záliš, S.; Gray, H. B.; Vlček, A.; Winkler, J. R. Two Tryptophans Are Better Than One in Accelerating Electron Flow through a Protein. ACS Cent. Sci. 2019, 5 (1), 192– 200,  DOI: 10.1021/acscentsci.8b00882

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    Two tryptophans are better than one in accelerating electron flow through a protein

    Takematsu, Kana; Williamson, Heather R.; Nikolovski, Pavle; Kaiser, Jens T.; Sheng, Yuling; Pospisil, Petr; Towrie, Michael; Heyda, Jan; Hollas, Daniel; Zalis, Stanislav; Gray, Harry B.; Vlcek, Antonin; Winkler, Jay R.

    ACS Central Science (2019), 5 (1), 192-200CODEN: ACSCII; ISSN:2374-7951. (American Chemical Society)

    We constructed and structurally characterized a Pseudomonas aeruginosa azurin mutant, Re126WWCuI, where 2 adjacent Trp (W) residues (Trp-124 and Trp-122; indole sepn., 3.6-4.1 Å) were inserted between the CuI center and a Re photosensitizer was coordinated to the imidazole of His-126 (ReI(H126)(CO)3(4,7-dimethyl-1,10-phenanthroline)+). CuI oxidn. by the photoexcited Re label (*Re) 22.9 Å away proceeded with a ∼70-ns time const., similar to that of a single-Trp mutant (∼40 ns) with a 19.4 Å Re-Cu distance. Time-resolved spectroscopy (luminescence, visible, and IR absorption) revealed 2 rapid reversible electron transfer steps, Trp-124 → *Re (400-475 ps, K1 ≃ 3.5-4) and Trp-122 → W124•+ (7-9 ns, K2 ≃ 0.55-0.75), followed by a rate-detg. (70-90 ns) CuI oxidn. by W122•+ ∼11 Å away. The photocycle was completed by 120-μs recombination. No photochem. CuI oxidn. was obsd. in Re126FWCuI, whereas in Re126WFCuI, the photocycle was restricted to the ReH126W124 unit and CuI remained isolated. QM/MM/MD simulations of Re126WWCuI indicated that indole solvation changed through the hopping process and Trp-124 → *Re electron transfer was accompanied by water fluctuations that tightened Trp-124 solvation. Our finding that multistep tunneling (hopping) confers an ∼9000-fold advantage over single-step tunneling in the double-Trp protein supported the proposal that hole-hopping through Trp/Tyr chains protects enzymes from oxidative damage.

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56. 56

    Sarhangi, S. M.; Matyushov, D. V. Theory of Protein Charge Transfer: Electron Transfer between Tryptophan Residue and Active Site of Azurin. J. Phys. Chem. B 2022, 126 (49), 10360– 10373,  DOI: 10.1021/acs.jpcb.2c05258

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    Theory of Protein Charge Transfer: Electron Transfer between Tryptophan Residue and Active Site of Azurin

    Sarhangi, Setare Mostajabi; Matyushov, Dmitry V.

    Journal of Physical Chemistry B (2022), 126 (49), 10360-10373CODEN: JPCBFK; ISSN:1520-5207. (American Chemical Society)

    One reaction step in the cond. relay of azurin, electron transfer between the Cu-based active site and the tryptophan residue, was studied theor. and by classical mol. dynamics simulations. Oxidn. of tryptophan results in electrowetting of this residue. This structural change makes the free energy surfaces of electron transfer nonparabolic as described by the Q-model of electron transfer. The authors analyze the medium dynamical effect on protein electron transfer produced by coupled Stokes-shift dynamics and the dynamics of the donor-acceptor distance modulating electron tunneling. The equil. donor-acceptor distance falls in the plateau region of the rate const., where it is detd. by the protein-water dynamics, and the probability of electron tunneling does not affect the rate. The crossover distance found here puts most intraprotein electron-transfer reactions under the umbrella of dynamical control. The crossover between the medium-controlled and tunneling-controlled kinetics is combined with the effect of the protein-water medium on the activation barrier to formulate principles of tunability of protein-based charge-transfer chains. The main principle in optimizing the activation barrier is the departure from the Gaussian-Gibbsian statistics of fluctuations promoting activated transitions. This is achieved either by incomplete (nonergodic) sampling, breaking the link between the Stokes-shift and variance reorganization energies, or through wetting-induced structural changes of the enzyme's active site.

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57. 57

    Olloqui-Sariego, J. L.; Zakharova, G. S.; Poloznikov, A. A.; Calvente, J. J.; Hushpulian, D. M.; Gorton, L.; Andreu, R. Influence of Tryptophan Mutation on the Direct Electron Transfer of Immobilized Tobacco Peroxidase. Electrochim. Acta 2020, 351, 136465,  DOI: 10.1016/j.electacta.2020.136465

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    Influence of tryptophan mutation on the direct electron transfer of immobilized tobacco peroxidase

    Olloqui-Sariego, Jose Luis; Zakharova, Galina S.; Poloznikov, Andrey A.; Calvente, Juan Jose; Hushpulian, Dmitry M.; Gorton, Lo; Andreu, Rafael

    Electrochimica Acta (2020), 351 (), 136465CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)

    A major challenge in the design of electrochem. biodevices is to achieve fast rates of electron exchange between proteins and electrodes. In this work, we show that a significant increase in the direct electron transfer rate between a graphite electrode and Tobacco Peroxidase takes place when a surface exposed leucine, located in the vicinity of the heme pocket, is replaced by tryptophan. The anal. of the Fe(III)/Fe(II) voltammetric responses of native and mutated proteins, as a function of soln. pH and temp., leads to similar values of the redn. entropy and reorganization energy, but to a higher electronic coupling in the case of the mutant. In addn., the mutated and native proteins are shown to display similar electrocatalytic activities to reduce hydrogen peroxide at pos. potentials, indicating that the mol. structure of the heme pocket is largely unaffected by the mutation.

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58. 58

    Sugimoto, Y.; Kawai, S.; Kitazumi, Y.; Shirai, O.; Kano, K. Function of C-Terminal Hydrophobic Region in Fructose Dehydrogenase. Electrochim. Acta 2015, 176, 976– 981,  DOI: 10.1016/j.electacta.2015.07.142

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    Function of C-terminal hydrophobic region in fructose dehydrogenase

    Sugimoto, Yu; Kawai, Shota; Kitazumi, Yuki; Shirai, Osamu; Kano, Kenji

    Electrochimica Acta (2015), 176 (), 976-981CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)

    Fructose dehydrogenase (FDH) catalyzes oxidn. of D-fructose into 2-keto-D-fructose and is one of the enzymes allowing a direct electron transfer (DET)-type bioelectrocatalysis. FDH is a heterotrimeric membrane-bound enzyme (subunit I, II, and III) and subunit II has a C terminal hydrophobic region (CHR), which was expected to play a role in anchoring to membranes from the amino acid sequence. We have constructed a mutated FDH lacking of CHR (ΔchrFDH). Contrary to the expected function of CHR, ΔchrFDH is expressed in the membrane fraction, and subunit I/III subcomplex (ΔcFDH) is also expressed in a similar activity level but in the sol. fraction. In addn., the enzyme activity of the purified ΔchrFDH is about one twentieth of the native FDH. These results indicate that CHR is concerned with the binding between subunit I(/III) and subunit II and then with the enzyme activity. ΔChrFDH has clear DET activity that is larger than that expected from the soln. activity, and the characteristics of the catalytic wave of ΔchrFDH are very similar to those of FDH. The deletion of CHR seems to increase the amts. of the enzyme with the proper orientation for the DET reaction at electrode surfaces. Gel filtration chromatog. coupled with urea treatment shows that the binding in ΔchrFDH is stronger than that in FDH. It can be considered that the rigid binding between subunit I(/III) and II without CHR results in a conformation different from the native one, which leads to the decrease in the enzyme activity in soln.

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    Winkler, J. R.; Gray, H. B. Electron Flow through Metalloproteins. Chem. Rev. 2014, 114 (7), 3369– 3380,  DOI: 10.1021/cr4004715

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    Electron flow through metalloproteins

    Winkler, Jay R.; Gray, Harry B.

    Chemical Reviews (Washington, DC, United States) (2014), 114 (7), 3369-3380CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)

    A review. Electron flow through proteins and protein assemblies in the photosynthetic and respiratory machinery commonly occurs between metal centers or other redox cofactors that are sepd. by relatively large mol. distances, often in the 10-20 Å range. Here, long-range electron transfer in metalloproteins is discussed. A key finding from these studies is that macromol. structures tune thermodn. properties and electronic coupling interactions to facilitate electron flow through biol. redox chains.

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60. 60

    Page, C. C.; Moser, C. C.; Chen, X.; Dutton, P. L. Natural Engineering Principles of Electron Tunnelling in Biological Oxidation-Reduction. Nature 1999, 402 (6757), 47– 52,  DOI: 10.1038/46972

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    Natural engineering principles of electron tunneling in biological oxidation-reduction

    Page, Christopher C.; Moser, Christopher C.; Chen, Xiaoxi; Dutton, P. Leslie

    Nature (London) (1999), 402 (6757), 47-52CODEN: NATUAS; ISSN:0028-0836. (Macmillan Magazines)

    We have surveyed proteins with known at. structure whose function involves electron transfer; in these, electrons can travel up to 14 Å between redox centers through the protein medium. Transfer over longer distances always involves a chain of cofactors. This redox center proximity alone is sufficient to allow tunneling of electrons at rates far faster than the substrate redox reactions it supports. Consequently, there has been no necessity for proteins to evolve optimized routes between redox centers. Instead, simple geometry enables rapid tunneling to high-energy intermediate states. This greatly simplifies any anal. of redox protein mechanisms and challenges the need to postulate mechanisms of superexchange through redox centers or the maintenance of charge neutrality when investigating electron-transfer reactions. Such tunneling also allows sequential electron transfer in catalytic sites to surmount radical transition states without involving the movement of hydride ions, as is generally assumed. The 14 Å or less spacing of redox centers provides highly robust engineering for electron transfer, and may reflect selection against designs that have proved more vulnerable to mutations during the course of evolution.

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61. 61

    Matsushita, K.; Kobayashi, Y.; Mizuguchi, M.; Toyama, H.; Adachi, O.; Sakamoto, K.; Miyoshi, H. A Tightly Bound Quinone Functions in the Ubiquinone Reaction Sites of Quinoprotein Alcohol Dehydrogenase of an Acetic Acid Bacterium, Gluconobacter Suboxydans. Biosci. Biotechnol. Biochem. 2008, 72 (10), 2723– 2731,  DOI: 10.1271/bbb.80363

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    A tightly bound quinone functions in the ubiquinone reaction sites of quinoprotein alcohol dehydrogenase of an acetic acid bacterium, Gluconobacter suboxydans

    Matsushita, Kazunobu; Kobayashi, Yoshiki; Mizuguchi, Mitsuhiro; Toyama, Hirohide; Adachi, Osao; Sakamoto, Kimitoshi; Miyoshi, Hideto

    Bioscience, Biotechnology, and Biochemistry (2008), 72 (10), 2723-2731CODEN: BBBIEJ; ISSN:0916-8451. (Japan Society for Bioscience, Biotechnology, and Agrochemistry)

    Quinoprotein alc. dehydrogenase (ADH) of acetic acid bacteria is a membrane-bound enzyme that functions as the primary dehydrogenase in the ethanol oxidase respiratory chain. It consists of three subunits and has a pyrroloquinoline quinone (PQQ) in the active site and four heme c moieties as electron transfer mediators. Of these, three heme c sites and a further site have been found to be involved in ubiquinone (Q) redn. and ubiquinol (QH2) oxidn. resp. In this study, ADH solubilized and purified with dodecyl maltoside, but not with Triton X-100, had a tightly bound Q, and thus two different ADHs, one having the tightly bound Q (Q-bound ADH) and Q-free ADH, could be obtained. The Q-binding sites of both the ADHs were characterized using specific inhibitors, a substituted phenol PC16 (a Q analog inhibitor) and antimycin A. Based on the inhibition kinetics of Q2 reductase and ubiquinol-2 (Q2H2) oxidase activities, it was suggested that there are one and two PC16-binding sites in Q-bound ADH and Q-free ADH resp. With antimycin A, only one binding site was found for Q2 reductase and Q2H2 oxidase activities, irresp. of the presence of bound Q. These results suggest that ADH has a high-affinity Q binding site (QH) besides low-affinity Q redn. and QH2 oxidn. sites, and that the bound Q in the QH site is involved in the electron transfer between heme c moieties and bulk Q or QH2 in the low-affinity sites.

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62. 62

    Yakushi, T.; Matsushita, K. Alcohol Dehydrogenase of Acetic Acid Bacteria: Structure, Mode of Action, and Applications in Biotechnology. Appl. Microbiol. Biotechnol. 2010, 86 (5), 1257– 1265,  DOI: 10.1007/s00253-010-2529-z

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    Alcohol dehydrogenase of acetic acid bacteria: structure, mode of action, and applications in biotechnology

    Yakushi, Toshiharu; Matsushita, Kazunobu

    Applied Microbiology and Biotechnology (2010), 86 (5), 1257-1265CODEN: AMBIDG; ISSN:0175-7598. (Springer)

    A review. Pyrroquinoline quinone-dependent alc. dehydrogenase (PQQ-ADH) of acetic acid bacteria is a membrane-bound enzyme involved in the acetic acid fermn. by oxidizing ethanol to acetaldehyde coupling with redn. of membranous ubiquinone (Q), which is, in turn, re-oxidized by ubiquinol oxidase, reducing oxygen to water. PQQ-ADHs seem to have co-evolved with the organisms fitting to their own habitats. The enzyme consists of three subunits and has a pyrroloquinoline quinone, 4 heme c moieties, and a tightly bound Q as the electron transfer mediators. Biochem., genetic, and electrochem. studies have revealed the unique properties of PQQ-ADH since it was purified in 1978. The enzyme is unique to have ubiquinol oxidn. activity in addn. to Q redn. This mini-review focuses on the mol. properties of PQQ-ADH, such as the roles of the subunits and the cofactors, particularly in intramol. electron transport of the enzyme from ethanol to Q. Also, we summarize biotechnol. applications of PQQ-ADH as to enantiospecific oxidns. for prodn. of the valuable chems. and bioelectrocatalysis for sensors and fuel cells using indirect and direct electron transfer technologies and discuss unsolved issues and future prospects related to this elaborate enzyme.

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63. 63

    Adachi, T.; Miyata, T.; Makino, F.; Tanaka, H.; Namba, K.; Kano, K.; Sowa, K.; Kitazumi, Y.; Shirai, O. Experimental and Theoretical Insights into Bienzymatic Cascade for Mediatorless Bioelectrochemical Ethanol Oxidation with Alcohol and Aldehyde Dehydrogenases. ACS. Catal. 2023, 13, 7955– 7965,  DOI: 10.1021/acscatal.3c01962

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    63

    Experimental and Theoretical Insights into Bienzymatic Cascade for Mediatorless Bioelectrochemical Ethanol Oxidation with Alcohol and Aldehyde Dehydrogenases

    Adachi, Taiki; Miyata, Tomoko; Makino, Fumiaki; Tanaka, Hideaki; Namba, Keiichi; Kano, Kenji; Sowa, Keisei; Kitazumi, Yuki; Shirai, Osamu

    ACS Catalysis (2023), 13 (12), 7955-7965CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)

    The efficient utilization of biomass fuels is a crit. component of a sustainable energy economy. Via respiration, acetic acid bacteria can oxidize biomass ethanol into acetic acid using membrane-bound alc. and aldehyde dehydrogenases (ADH and AlDH, resp.). Focusing on the ability of these enzymes to interact directly and elec. with electrode materials, we constructed a mediatorless bioanode for ethanol oxidn. based on a direct electron transfer (DET)-type bienzymic cascade by ADH and AlDH. The three-dimensional structural data of ADH and AlDH elucidated by cryo-electron microscopy were valuable for effectively designing electrode platforms with multi-walled carbon nanotubes (MWCNTs) and pyrene (Py) derivs. DET-type bioelectrocatalysis by ADH and AlDH was improved by using 1-pyrene carboxylic acid-functionalized MWCNTs. The catalytic current densities for bienzymic ethanol oxidn. were recorded at the bioanodes modified by various ADH/AlDH ratios. The reaction model was constructed by focusing on the competitive adsorption of two enzymes on the electrode surface and the collection efficiency of the intermediately produced acetaldehyde. The power output of an ethanol/air biofuel cell using the bienzymic bioanode reached 0.48 ± 0.01 mW cm-2, which is the highest value reported for ethanol biofuel cells. In addn., the Faraday efficiency of acetate prodn. by the cell reached 100 ± 4%. This study will lead to efficient conversion of biomass fuels based on a multi-catalytic cascade system.

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64. 64

    Bollella, P.; Hibino, Y.; Kano, K.; Gorton, L.; Antiochia, R. The Influence of pH and Divalent/Monovalent Cations on the Internal Electron Transfer (IET), Enzymatic Activity, and Structure of Fructose Dehydrogenase. Anal. Bioanal. Chem. 2018, 410 (14), 3253– 3264,  DOI: 10.1007/s00216-018-0991-0

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    The influence of pH and divalent/monovalent cations on the internal electron transfer (IET), enzymatic activity, and structure of fructose dehydrogenase

    Bollella, Paolo; Hibino, Yuya; Kano, Kenji; Gorton, Lo; Antiochia, Riccarda

    Analytical and Bioanalytical Chemistry (2018), 410 (14), 3253-3264CODEN: ABCNBP; ISSN:1618-2642. (Springer)

    We report on the influence of pH and monovalent/divalent cations on the catalytic current response, internal electron transfer (IET), and structure of fructose dehydrogenase (FDH) by using amperometry, spectrophotometry, and CD. Amperometric measurements were performed on graphite electrodes, onto which FDH was adsorbed and the effect on the response current to fructose was investigated when varying the pH and the concns. of divalent/monovalent cations in the contacting buffer. In the presence of 10 mM CaCl2, a current increase of up to ≈ 240% was obsd., probably due to an intra-complexation reaction between Ca2+ and the aspartate/glutamate residues found at the interface between the dehydrogenase domain and the cytochrome domain of FDH. Contrary to CaCl2, addn. of MgCl2 did not show any particular influence, whereas addn. of monovalent cations (Na+ or K+) led to a slight linear increase in the max. response current. To complement the amperometric investigations, spectrophotometric assays were carried out under homogeneous conditions in the presence of a 1-electron non-proton-acceptor, cytochrome c, or a 2-electron-proton acceptor, 2,6-dichloroindophenol (DCIP), resp. In the case of cytochrome c, it was possible to observe a remarkable increase in the absorbance up to 200% when 10 mM CaCl2 was added. However, by further increasing the concn. of CaCl2 up to 50 mM and 100 mM, a decrease in the absorbance with a slight inhibition effect was obsd. for the highest CaCl2 concn. Addn. of MgCl2 or of the monovalent cations shows, surprisingly, no effect on the electron transfer to the electron acceptor. Contrary to the case of cytochrome c, with DCIP none of the cations tested seem to affect the rate of catalysis. In order to correlate the results obtained by amperometric and spectrophotometric measurements, CD expts. have been performed showing a great structural change of FDH when increasing the concn. CaCl2 up to 50 mM, at which the enzyme mols. start to agglomerate, hindering the substrate access to the active site probably due to a chelation reaction occurring at the enzyme surface with the glutamate/aspartate residues.

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65. 65

    Jumper, J.; Evans, R.; Pritzel, A.; Green, T.; Figurnov, M.; Ronneberger, O.; Tunyasuvunakool, K.; Bates, R.; Žídek, A.; Potapenko, A.; Bridgland, A.; Meyer, C.; Kohl, S. A. A.; Ballard, A. J.; Cowie, A.; Romera-Paredes, B.; Nikolov, S.; Jain, R.; Adler, J.; Back, T.; Petersen, S.; Reiman, D.; Clancy, E.; Zielinski, M.; Steinegger, M.; Pacholska, M.; Berghammer, T.; Bodenstein, S.; Silver, D.; Vinyals, O.; Senior, A. W.; Kavukcuoglu, K.; Kohli, P.; Hassabis, D. Highly Accurate Protein Structure Prediction with AlphaFold. Nature 2021, 596 (7873), 583– 589,  DOI: 10.1038/s41586-021-03819-2

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    Highly accurate protein structure prediction with AlphaFold

    Jumper, John; Evans, Richard; Pritzel, Alexander; Green, Tim; Figurnov, Michael; Ronneberger, Olaf; Tunyasuvunakool, Kathryn; Bates, Russ; Zidek, Augustin; Potapenko, Anna; Bridgland, Alex; Meyer, Clemens; Kohl, Simon A. A.; Ballard, Andrew J.; Cowie, Andrew; Romera-Paredes, Bernardino; Nikolov, Stanislav; Jain, Rishub; Adler, Jonas; Back, Trevor; Petersen, Stig; Reiman, David; Clancy, Ellen; Zielinski, Michal; Steinegger, Martin; Pacholska, Michalina; Berghammer, Tamas; Bodenstein, Sebastian; Silver, David; Vinyals, Oriol; Senior, Andrew W.; Kavukcuoglu, Koray; Kohli, Pushmeet; Hassabis, Demis

    Nature (London, United Kingdom) (2021), 596 (7873), 583-589CODEN: NATUAS; ISSN:0028-0836. (Nature Portfolio)

    Proteins are essential to life, and understanding their structure can facilitate a mechanistic understanding of their function. Through an enormous exptl. effort, the structures of around 100,000 unique proteins have been detd., but this represents a small fraction of the billions of known protein sequences. Structural coverage is bottlenecked by the months to years of painstaking effort required to det. a single protein structure. Accurate computational approaches are needed to address this gap and to enable large-scale structural bioinformatics. Predicting the three-dimensional structure that a protein will adopt based solely on its amino acid sequence-the structure prediction component of the 'protein folding problem'-has been an important open research problem for more than 50 years. Despite recent progress, existing methods fall far short of at. accuracy, esp. when no homologous structure is available. Here we provide the first computational method that can regularly predict protein structures with at. accuracy even in cases in which no similar structure is known. We validated an entirely redesigned version of our neural network-based model, AlphaFold, in the challenging 14th Crit. Assessment of protein Structure Prediction (CASP14), demonstrating accuracy competitive with exptl. structures in a majority of cases and greatly outperforming other methods. Underpinning the latest version of AlphaFold is a novel machine learning approach that incorporates phys. and biol. knowledge about protein structure, leveraging multi-sequence alignments, into the design of the deep learning algorithm.

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    Marcus, R. A.; Sutin, N. Electron transfers in chemistry and biology. Biochim. Biophys. Acta. Bioenerg. 1985, 811 (3), 265– 322,  DOI: 10.1016/0304-4173(85)90014-X

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    Electron transfers in chemistry and biology

    Marcus, R. A.; Sutin, Norman

    Biochimica et Biophysica Acta, Reviews on Bioenergetics (1985), 811 (3), 265-322CODEN: BRBECF; ISSN:0304-4173.

    A review, with 331 refs., of the theory of electron-transfer reactions in soln., comparison of predictions with exptl. measurements in nonbiol. systems, and the extension and application of this theory to biol. electron-transfer reactions.

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    Lowe, H.J.; Clark, W. M. Studies on Oxidation-Reduction. XXIV. Oxidation-Reduction Potentials of Flavin Adenine Dinucleotide. J. Biol. Chem. 1956, 221 (2), 983– 992,  DOI: 10.1016/S0021-9258(18)65211-1

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    Oxidation-reduction. XXIV. Oxidation-reduction potentials of flavine adenine dinucleotide

    Lowe, H. J.; Clark, W. Mansfield

    Journal of Biological Chemistry (1956), 221 (), 983-92CODEN: JBCHA3; ISSN:0021-9258.

    cf. C.A. 30, 6268.8. Potentiometric titration curves for flavine adenine dinucleotide (FAD) in the pH range 2.4-12.4 and for flavine mononucleotide (FMN) in the pH range 0.89-10.9 indicate that the oxidation-reduction process is reversible and involves the formation of a semiquinone as an intermediate in the 2-equiv. change. When appropriate corrections are made for pos. drifts of potential encountered near the end points in rapid titrations at low concns. of FAD, the exptl. points agree closely with the theoretical values calcd. for a 2-equiv. change with semiquinone formation. The greater stability of potentials during titrations of more concd. solns. of FMN increases the significance of the calcns. for the amt. of semiquinone formed at 50% reduction. At const. pH, the slopes of the titration curves for FMN increase with increasing concns. of FMN and indicate the formation of a dimer. For descriptive purposes the potentials at 50% a reduction (EM) as a function of H ion activity (H+) can be formulated by the equation: EM = E0 -0.0601 pH + 0.03005 log [Kr' + (H+)]/[Ko' + (H+)] where E0 = 0.187 v., Kr' = 2 × 10-7, KO' = 4 × 10-11. The precision of the data is not such that distinctions can be made between values for FAD and values for FMN. EM at pH 7.0 = -0.219 v. calcd.

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68. 68

    Moser, C. C.; Keske, J. M.; Warncke, K.; Farid, R. S.; Dutton, P. L. Nature of Biological Electron Transfer. Nature 1992, 355 (6363), 796– 802,  DOI: 10.1038/355796a0

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    Nature of biological electron transfer

    Moser, Christopher C.; Keske, Jonathan M.; Warncke, Kurt; Farid, Ramy S.; Dutton, P. Leslie

    Nature (London, United Kingdom) (1992), 355 (6363), 796-802CODEN: NATUAS; ISSN:0028-0836.

    Factors which govern long-range electron transfer in biol. systems are examd. A powerful first-order anal. of intraprotein electron transfer is developed from electron-transfer measurements both in biol. and chem. systems. The anal. provides guidelines basic to the understanding of the design and engineering of respiratory and photosynthetic electron-transfer chains and other redox proteins.

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69. 69

    Farver, O.; Skov, L. K.; Pascher, T.; Karlsson, B. G.; Nordling, M.; Lundberg, L. G.; Vaenngaard, T.; Pecht, I. Intramolecular Electron Transfer in Single-Site-Mutated Azurins. Biochemistry 1993, 32 (28), 7317– 7322,  DOI: 10.1021/bi00079a031

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    Intramolecular electron transfer in single-site-mutated azurins

    Farver, Ole; Skov, Lars K.; Pascher, Torbjoern; Karlsson, B. Goeran; Nordling, Margareta; Lundberg, Lennart G.; Vaenngaard, Tore; Pecht, Israel

    Biochemistry (1993), 32 (28), 7317-22CODEN: BICHAW; ISSN:0006-2960.

    Single-site mutants of the blue, single-copper protein, azurin, from Pseudomonas aeruginosa were reduced by CO2- radicals in pulse radiolysis expts. The single disulfide group was reduced directly by CO2- with rates similar to those of the native protein. The RSSR- radical produced in the above reaction was reoxidized in a slower intramol. electron-transfer process (30-70 s-1 at 298 K) concomitant with a further redn. of the Cu(II) ion. The temp. dependence of the latter rates was detd. and used to derive information on the possible effects of the mutations. The substitution of residue Phe114, situated on the opposite side of Cu relative to the disulfide, by Ala resulted in a rate increase by a factor of almost 2. By assuming that this effect is only due to an increase in driving force, λ = 135 kJ mol-1 for the reorganization energy was derived. When Trp48, situated midway between the donor and the acceptor, was replaced by Leu or Met, only a small change in the rate of intramol. electron transfer was obsd., indicating that the arom. residue in this position is apparently only marginally involved in electron transfer in wild-type azurin. Pathway calcns. also suggest that a longer, through-backbone path is more efficient that the shorter one involving Trp48. The former pathway yields an exponential decay factor, β, of 6.6 nm-1. Another mutation, raising the electron-transfer driving force, was produced by changing the Cu ligand Met121 to Leu, which increases the redn. potential by 100 mV. However, the increase in rate was less than expected from the larger driving force and is probably compensated by a small increase in λ. Marcus theory anal. shows that the obsd. rates are in accordance with a through-bond electron-transfer mechanism.

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70. 70

    Beratan, D. N.; Onuchic, J. N.; Betts, J. N.; Bowler, B. E.; Gray, H. B. Electron-Tunneling Pathways in Ruthenated Proteins. J. Am. Chem. Soc. 1990, 112 (22), 7915– 7921,  DOI: 10.1021/ja00178a011

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    Electron tunneling pathways in ruthenated proteins

    Beratan, David N.; Onuchic, Jose Nelson; Betts, Jonathan N.; Bowler, Bruce E.; Gray, Harry B.

    Journal of the American Chemical Society (1990), 112 (22), 7915-21CODEN: JACSAT; ISSN:0002-7863.

    A numerical algorithm was used to survey proteins for electron tunneling pathways. Insight was gained into the nature of the mediation process in long-distance electron-transfer reactions. The dominance of covalent and H-bond pathways is shown. The method predicts the relative electronic couplings in ruthenated myoglobin and cytochrome c consistent with measured electron-transfer rates. It also allows the design of long-range electron-transfer systems. Qual. differences between pathways arise from differences in the protein secondary structure. Effects of this sort are not predicted from simpler models that neglect various details of the protein electronic structure.

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71. 71

    Dolinsky, T. J.; Nielsen, J. E.; McCammon, J. A.; Baker, N. A. PDB2PQR: An Automated Pipeline for the Setup of Poisson-Boltzmann Electrostatics Calculations. Nucleic Acids Res. 2004, 32 (Web Server), W665– W667,  DOI: 10.1093/nar/gkh381

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    71

    PDB2PQR: An automated pipeline for the setup of Poisson-Boltzmann electrostatics calculations

    Dolinsky, Todd J.; Nielsen, Jens E.; McCammon, J. Andrew; Baker, Nathan A.

    Nucleic Acids Research (2004), 32 (Web Server), W665-W667CODEN: NARHAD; ISSN:0305-1048. (Oxford University Press)

    Continuum solvation models, such as Poisson-Boltzmann and Generalized Born methods, have become increasingly popular tools for investigating the influence of electrostatics on biomol. structure, energetics and dynamics. However, the use of such methods requires accurate and complete structural data as well as force field parameters such as at. charges and radii. Unfortunately, the limiting step in continuum electrostatics calcns. is often the addn. of missing at. coordinates to mol. structures from the Protein Data Bank and the assignment of parameters to biomol. structures. To address this problem, we have developed the PDB2PQR web service (http://agave.wustl.edu/pdb2pqr/). This server automates many of the common tasks of prepg. structures for continuum electrostatics calcns., including adding a limited no. of missing heavy atoms to biomol. structures, estg. titrn. states and protonating biomols. in a manner consistent with favorable hydrogen bonding, assigning charge and radius parameters from a variety of force fields, and finally generating "PQR" output compatible with several popular computational biol. packages. This service is intended to facilitate the setup and execution of electrostatics calcns. for both experts and non-experts and thereby broaden the accessibility to the biol. community of continuum electrostatics analyses of biomol. systems.

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72. 72

    Baker, N. A.; Sept, D.; Joseph, S.; Holst, M. J.; McCammon, J. A. Electrostatics of Nanosystems: Application to Microtubules and the Ribosome. Proc. Natl. Acad. Sci. U. S. A. 2001, 98 (18), 10037– 10041,  DOI: 10.1073/pnas.181342398

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    72

    Electrostatics of nanosystems: application to microtubules and the ribosome

    Baker, Nathan A.; Sept, David; Joseph, Simpson; Holst, Michael J.; McCammon, J. Andrew

    Proceedings of the National Academy of Sciences of the United States of America (2001), 98 (18), 10037-10041CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)

    Evaluation of the electrostatic properties of biomols. has become a std. practice in mol. biophysics. Foremost among the models used to elucidate the electrostatic potential is the Poisson-Boltzmann equation; however, existing methods for solving this equation have limited the scope of accurate electrostatic calcns. to relatively small biomol. systems. Here we present the application of numerical methods to enable the trivially parallel soln. of the Poisson-Boltzmann equation for supramol. structures that are orders of magnitude larger in size. As a demonstration of this methodol., electrostatic potentials have been calcd. for large microtubule and ribosome structures. The results point to the likely role of electrostatics in a variety of activities of these structures.

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73. 73

    Bollella, P.; Hibino, Y.; Kano, K.; Gorton, L.; Antiochia, R. Highly Sensitive Membraneless Fructose Biosensor Based on Fructose Dehydrogenase Immobilized onto Aryl Thiol Modified Highly Porous Gold Electrode: Characterization and Application in Food Samples. Anal. Chem. 2018, 90 (20), 12131– 12136,  DOI: 10.1021/acs.analchem.8b03093

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    73

    Highly Sensitive Membraneless Fructose Biosensor Based on Fructose Dehydrogenase Immobilized onto Aryl Thiol Modified Highly Porous Gold Electrode: Characterization and Application in Food Samples

    Bollella, Paolo; Hibino, Yuya; Kano, Kenji; Gorton, Lo; Antiochia, Riccarda

    Analytical Chemistry (Washington, DC, United States) (2018), 90 (20), 12131-12136CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)

    In this paper we present a new method to electrodeposit highly porous gold (h-PG) onto a polycryst. solid gold electrode without any template. The electrodeposition is carried out by first cycling the electrode potential between +0.8 and 0 V in 10 mM HAuCl4 with 2.5 M NH4Cl and then applying a neg. potential for the prodn. of hydrogen bubbles at the electrode surface. After that the modified electrode was characterized in sulfuric acid to est. the real surface area (Areal) to be close to 24 cm2, which is roughly 300 times higher compared to the bare gold electrodes (0.08 cm2). The electrode was further incubated overnight with three different thiols (4-mercaptobenzoic acid (4-MBA), 4-mercaptophenol (4-MPh), and 4-aminothiophenol (4-APh)) in order to produce differently charged self-assembled monolayers (SAMs) on the electrode surface. Finally a fructose dehydrogenase (FDH) soln. was drop-cast onto the electrodes. All the modified electrodes were investigated by cyclic voltammetry both under nonturnover and turnover conditions. The FDH/4-MPh/h-PG exhibited two couples of redox peaks for the heme c1 and heme c2 of the cytochrome domain of FDH and as well as a well pronounced catalytic c.d. (about 1000 μA cm-2 in the presence of 10 mM fructose) due to the presence of -OH groups on the electrode surface, which stabilize and orientate the enzyme layer on the electrode surface. The FDH/4-MPh/h-PG based electrode showed the best anal. performance with an excellent stability (90% retained activity over 90 days), a detection limit of 0.3 μM fructose, a linear range between 0.05 and 5 mM, and a sensitivity of 175 ± 15 μA cm-2 mM-1. These properties were favorably compared with other fructose biosensors reported in the literature. The biosensor was successively tested to quantify the fructose content in food and beverage samples. No significant interference present in the sample matrixes was obsd.

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74. 74

    Bocanegra-Rodríguez, S.; Molins-Legua, C.; Campíns-Falcó, P.; Giroud, F.; Gross, A. J.; Cosnier, S. Monofunctional Pyrenes at Carbon Nanotube Electrodes for Direct Electron Transfer H₂O₂ Reduction with HRP and HRP-Bacterial Nanocellulose. Biosens. Bioelectron. 2021, 187, 113304,  DOI: 10.1016/j.bios.2021.113304

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    74

    Monofunctional pyrenes at carbon nanotube electrodes for direct electron transfer H2O2 reduction with HRP and HRP-bacterial nanocellulose

    Bocanegra-Rodriguez, Sara; Molins-Legua, Carmen; Campins-Falco, Pilar; Giroud, Fabien; Gross, Andrew J.; Cosnier, Serge

    Biosensors & Bioelectronics (2021), 187 (), 113304CODEN: BBIOE4; ISSN:0956-5663. (Elsevier B.V.)

    The non-covalent modification of carbon nanotube electrodes with pyrene derivs. is a versatile approach to enhance the elec. wiring of enzymes for biosensors and biofuel cells. We report here a comparative study of five pyrene derivs. adsorbed at multi-walled carbon nanotube electrodes to shed light on their ability to promote direct electron transfer with horseradish peroxidase (HRP) for H2O2 redn. In all cases, pyrene-modified electrodes enhanced catalytic redn. compared to the unmodified electrodes. The pyrene N-hydroxysuccinimide (NHS) ester deriv. provided access to the highest catalytic current of 1.4 mA cm-2 at 6 mmol L-1 H2O2, high onset potential of 0.61 V vs. Ag/AgCl, insensitivity to parasitic H2O2 oxidn., and a large linear dynamic range that benefits from insensitivity to HRP "suicide inactivation" at 4-6 mmol L-1 H2O2. Pyrene-aliph. carboxylic acid groups offer better sensor sensitivity and higher catalytic currents at ≤ 1 mmol L-1 H2O2 concns. The butyric acid and NHS ester derivs. gave high anal. sensitivities of 5.63 A M-1 cm-2 and 2.96 A M-1 cm-2, resp., over a wide range (0.25-4 mmol-1) compared to existing carbon-based HRP biosensor electrodes. A bacterial nanocellulose pyrene-NHS HRP bioelectrode was subsequently elaborated via "one-pot" and "layer-by-layer" strategies. The optimized bioelectrode exhibited slightly weaker voltage output, further enhanced catalytic currents, and a major enhancement in 1-wk stability with 67% activity remaining compared to 39% at the equiv. electrode without nanocellulose, thus offering excellent prospects for biosensing and biofuel cell applications.

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75. 75

    Blanford, C. F.; Heath, R. S.; Armstrong, F. A. A Stable Electrode for High-Potential, Electrocatalytic O₂ Reduction Based on Rational Attachment of a Blue Copper Oxidase to a Graphite Surface. Chem. Commun. 2007, (17), 1710– 1712,  DOI: 10.1039/b703114a

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    75

    A stable electrode for high-potential, electrocatalytic O2 reduction based on rational attachment of a blue copper oxidase to a graphite surface

    Blanford, Christopher F.; Heath, Rachel S.; Armstrong, Fraser A.

    Chemical Communications (Cambridge, United Kingdom) (2007), (17), 1710-1712CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)

    Attachment of substrate-like anthracene-based units to the surface of pyrolytic graphite enhances the adsorption of high-potential fungal laccases, blue Cu enzymes, that catalyze the 4-electron redn. of O2. This constitutes a stable cathode for enzymic biol. fuel cells and electrochem. studies.

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76. 76

    Meredith, M. T.; Minson, M.; Hickey, D.; Artyushkova, K.; Glatzhofer, D. T.; Minteer, S. D. Anthracene-Modified Multi-Walled Carbon Nanotubes as Direct Electron Transfer Scaffolds for Enzymatic Oxygen Reduction. ACS Catal. 2011, 1 (12), 1683– 1690,  DOI: 10.1021/cs200475q

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    76

    Anthracene-Modified Multi-Walled Carbon Nanotubes as Direct Electron Transfer Scaffolds for Enzymatic Oxygen Reduction

    Meredith, Matthew T.; Minson, Michael; Hickey, David; Artyushkova, Kateryna; Glatzhofer, Daniel T.; Minteer, Shelley D.

    ACS Catalysis (2011), 1 (12), 1683-1690CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)

    The development of new methods to facilitate direct electron transfer (DET) between enzymes and electrodes is of much interest because of the desire for stable biofuel cells that produce significant amts. of power. In this study, hydroxylated multiwalled carbon nanotubes (MWCNTs) were covalently modified with anthracene groups to help orient the active sites of laccase to allow for DET. The onset of the catalytic oxygen redn. current for these biocathodes occurred near the potential of the T1 active site of laccase, and optimized biocathodes produced background-subtracted current densities up to 140 μA/cm2. Potentiostatic and galvanostatic stability measurements of the biocathodes revealed losses of 25% and 30%, resp., after 24 h of const. operation. Finally, the novel biocathodes were utilized in biofuel cells employing two different anodic enzymes. A compartmentalized cell using a mediated glucose oxidase anode produced an open circuit voltage of 0.819 ± 0.022 V, a max. power d. of 56.8 (±1.8) μW/cm2, and a max. c.d. of 205.7 (±7.8) μA/cm2. A compartment-less cell using a DET fructose dehydrogenase anode produced an open circuit voltage of 0.707 ± 0.005 V, a max. power d. of 34.4 (±2.7) μW/cm2, and a max. c.d. of 201.7 (±14.4) μA/cm2.

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77. 77

    Bollella, P.; Hibino, Y.; Kano, K.; Gorton, L.; Antiochia, R. Enhanced Direct Electron Transfer of Fructose Dehydrogenase Rationally Immobilized on a 2-Aminoanthracene Diazonium Cation Grafted Single-Walled Carbon Nanotube Based Electrode. ACS Catal. 2018, 8 (11), 10279– 10289,  DOI: 10.1021/acscatal.8b02729

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    77

    Enhanced Direct Electron Transfer of Fructose Dehydrogenase Rationally Immobilized on a 2-Aminoanthracene Diazonium Cation Grafted Single-Walled Carbon Nanotube Based Electrode

    Bollella, Paolo; Hibino, Yuya; Kano, Kenji; Gorton, Lo; Antiochia, Riccarda

    ACS Catalysis (2018), 8 (11), 10279-10289CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)

    In this paper, an efficient direct electron transfer (DET) reaction was achieved between fructose dehydrogenase (FDH) and a glassy carbon electrode (GCE) onto which anthracene modified single walled carbon nanotubes were deposited. The SWCNTs were in situ activated with a diazonium salt synthesized through the reaction of 2-amino anthracene with NaNO2 in acidic media (0.5 M HCl) for 5 min at 0 °C. After the in situ reaction, the 2-amino anthracene diazonium salt was electrodeposited by running cyclic voltammograms from +1000 mV to -1000 mV vs. Ag|AgClsat. The anthracene-SWCNT modified GCE was further incubated in an FDH soln. to allow the enzyme to adsorb. Cyclic voltammograms of the FDH modified electrode revealed two couple of redox waves possibly ascribed to the heme c1 and heme c3 of the cytochrome domain. In the presence of 10 mM fructose two catalytic waves could clearly be seen and were correlated with two heme c:s (heme c1 and c2), with a max. c.d. of 485±21 μA cm-2 at 0.4 V vs. Ag|AgClsat at a sweep rate of 10 mVs-1. In contrast, for the plain SWCNT modified GCE only one catalytic wave and one couple of redox waves were obsd. Adsorbing FDH directly onto a GCE showed no non-turn over electrochem. of FDH and in the presence of fructose only a slight catalytic effect could be seen. These differences can be explained by considering the hydrophobic pocket close to heme c1, heme c2 and heme c3 of the cytochrome domain at which the anthracenyl arom. structure could interact through π-π interactions with the arom. side chains of the amino acids present in the hydrophobic pocket of FDH.

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78. 78

    Léger, C.; Jones, A. K.; Albracht, S. P. J.; Armstrong, F. A. Effect of a Dispersion of Interfacial Electron Transfer Rates on Steady State Catalytic Electron Transport in [NiFe]-Hydrogenase and Other Enzymes. J. Phys. Chem. B 2002, 106 (50), 13058– 13063,  DOI: 10.1021/jp0265687

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    78

    Effect of a Dispersion of Interfacial Electron Transfer Rates on Steady State Catalytic Electron Transport in [NiFe]-hydrogenase and Other Enzymes

    Leger, Christophe; Jones, Anne K.; Albracht, Simon P. J.; Armstrong, Fraser A.

    Journal of Physical Chemistry B (2002), 106 (50), 13058-13063CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)

    Redox enzymes can be adsorbed onto electrode surfaces such that there is a rapid and efficient direct electron transfer (ET) between the electrode and the enzyme's active site, along with high catalytic activity. In an idealized way, this may be analogous to protein-protein ET or, more significantly, the nonrigid interface between different domains of membrane-bound enzymes. The catalytic current that is obtained when substrate is added to the soln. is directly proportional to the enzyme's turnover rate and its dependence on the electrode potential reports on the energetics and kinetics of the entire catalytic cycle. Although the current is expected to reach a limiting value as the electrode potential is varied to increase the driving force, a residual slope in voltammograms is often obsd. This slope is significant, as it is unexpected from all simple considerations of electrochem. kinetics. A particularly remarkable result is obtained in expts. carried out with the [NiFe]-hydrogenase from Allochromatium vinosum: this enzyme displays high catalytic activity for hydrogen oxidn. and is easily studied up to 60°, at which temp. the current-potential response becomes completely linear over a range of more than 0.5 V. The explanation for this effect is that the enzyme mols. are not adsorbed in a homogeneous manner but vary in their degree of ET coupling with the electrode, i.e., through there being many slightly different orientations. Under conditions in which interfacial ET becomes rate-limiting, i.e., when turnover no. is high at elevated temps., the current-potential response reflects the superposition of numerous electrochem. rate consts. This is highly relevant in the interpretation of the catalytic electrochem. of enzymes.

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79. 79

    Sugimoto, Y.; Kitazumi, Y.; Shirai, O.; Kano, K. Effects of Mesoporous Structures on Direct Electron Transfer-Type Bioelectrocatalysis: Facts and Simulation on a Three-Dimensional Model of Random Orientation of Enzymes. Electrochemistry 2017, 85 (2), 82– 87,  DOI: 10.5796/electrochemistry.85.82

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    79

    Effects of mesoporous structures on direct electron transfer-type bioelectrocatalysis: facts and simulation on a three-dimensional model of random orientation of enzymes

    Sugimoto, Yu; Kitazumi, Yuki; Shirai, Osamu; Kano, Kenji

    Electrochemistry (Tokyo, Japan) (2017), 85 (2), 82-87CODEN: EECTFA; ISSN:1344-3542. (Electrochemical Society of Japan)

    Direct electron transfer (DET)-type bioelectrocatalytic waves of bilirubin oxidase (BOD)-catalyzed O2 redn. and [NiFe] hydrogenase (H2ase)-catalyzed H2 oxidn. are very small and un-detectable using glassy carbon (GC) electrodes, resp.; however, clear catalytic waves are obsd. when the enzymes are adsorbed on Ketjen black-modified GC (KB-GC) electrodes, in which KB provides mesopores for DET-type bioelectocatalysis. To explain the phenomena, we focus on the curvature effect of mesoporous structures on long range electron transfer kinetics and simulate steady-state voltammograms catalyzed by model redox enzymes adsorbed with a random orientation on planar and mesoporous electrodes based on a three-dimensional model. In the simulation, we assume a spherical enzyme with a radius of r1 an active site located at a certain distance from the center of the enzyme, and a spherical pore with a radius of Rp in mesoporous electrodes in which the enzyme is trapped and adsorbed. The simulation reveals that mesoporous electrodes provide platforms suitable for DET-type bioelectrocatalysis of enzymes when Rp becomes close to r. Such curvature effects of mesoporous electrodes become esp. notable for larger sized enzymes. Furthermore, the simulation reproduces the exptl. data of BOD- and H2ase- catalyzed DET-type waves by considering the crystal structures of the enzymes. This work will open a route to improve the kinetic performance of the DET-type bioelectrocatalysis that has become very important in its practical application to a variety of bioelectrochem. devices.

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