Intramolecular Electron Transfer in Pentaammineruthenium(III)-Modified Cobaltocytochrome c

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Abstract

The iron in the heme group of horse-heart cytochrome c was replaced by cobalt according to established methods. The resulting cobalticytochrome c was subsequently modified at histidine-33 with a pentaammineruthenium group. Proof of correct derivatization was obtained by atomic absorption analysis of cobalt and ruthenium, differential pulse voltammetry, and enzymatic proteolysis analyzed by diode-array HPLC. Cobalt(II)-to-ruthenium(III) intramolecular electron transfer rates were measured as a function of temperature by electron pulse radiolysis. The azide radical (N₃^•) was used to oxidize the fully reduced form in order to generate the desired electron transfer precursor. The intramolecular electron transfer rate is 1.28 ± 0.04 s^-1 at 25 °C (ΔH = 5.7 ± 0.2 kcal/mol, ΔS = −38.7 ± 0.5 cal/(deg mol)) for a driving force of 0.28 ± 0.02 eV. The results are compared with those for analogous pentaammineruthenium-modified, native iron, and zinc-substituted cytochromes c. The 0.4 eV increase in driving force for intramolecular electron transfer when iron is replaced by cobalt is largely compensated by an increase in reorganization energy.

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This article has been cited by 5 ACS Journal articles (5 most recent appear below).

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  Design and Characterization of A Synthetic Electron-Transfer Protein

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  Intramolecular Electron Transfer in Tetraammine(L)ruthenium(III)-Modified Manganocytochromes c

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  • Intramolecular Electron Transfer in Tetraammine(L)ruthenium(III)-Modified Manganocytochromes c

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• 

  pH and Driving Force Dependence of Intramolecular Oxyferryl Heme Reduction in Myoglobin

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• 

  Dependence of Intramolecular Electron-Transfer Rates on Driving Force, pH, and Temperature in Ammineruthenium-Modified Ferrocytochromes c

  James F. Wishart, Ji Sun, Myung Cho, Chang Su, and Stephan S. Isied
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  • Dependence of Intramolecular Electron-Transfer Rates on Driving Force, pH, and Temperature in Ammineruthenium-Modified Ferrocytochromes c

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    Several ruthenium ammine complexes were used to modify horse-heart cytochrome c at histidine-33, creating a series of (NH3)4(L)Ru−Cyt c derivatives (L = H2O/OH-, ammonia, 4-ethylpyridine, 3,5-lutidine, pyridine, isonicotinamide, N-methylpyrazinium) with a ...

    Abstract | Full Text HTML | Hi-Res PDF | PDF w/ Links

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