Cytochrome reversible electrode reaction

P. Yeh and T. Kuwana, Reversible electrode reaction of cytochrome c. Chem. Lett. 1145-1148 (1977). 

Reversible electrode reaction of cytochrome c. Chemistry Letters, 1145-1148. 

Yeh and Kuwana " were the first to report on the electrochemistry of cytochrome c at doped metal oxide semiconductor electrodes. A nearly reversible electrode reaction was indicated by the cyclic voltammetry and differential pulse voltammetry of cytochrome c at tin-doped indium oxide electrodes. Except for the calculated diffusion coefficient, all of the characteristics of the electrochemistry of cytochrome c at this electrode indicated that the electrode reaction was well-behaved. A value of 0.5 x 10" cmVs was determined for the diffusion coefficient which, like previously determined values at mercury, is lower than the value obtained by nonelectrochemical methods (i.e., 1.1 X 10 cm /s " " ). The electrochemical response of cytochrome c at tin oxide semiconductor electrodes was reported to be quasi-reversible, although no details were given. " ... 

It was shown that cleavage of the S—S bonding of 4-PySSPy takes place upon adsorption on both gold and silver electrodes, and a stable chemisorbed film is formed through sulfur to these electrodes [63, 65]. Cytochrome c adsorbed on a gold or silver electrode is displaced entirely by 4-PySSPy and the electrode reaction of cyt. c in the solution takes place through the PyS- film on the electrode surface [63, 64]. Added purine partially displaces cyt. c from a silver electrode surface and a mixed adsorbed layer of purine and cyt. c is formed, at which a reversible electrode reaction of cyt. c takes place [63]. 

Yeh, P. and Kuwana, T. (1977) "Reversible Electrode Reaction of Cytochrome c" Chem. Lett., 1145-8. 

The multiheme protein cytochrome C3, an electron transfer protein from the sulfate-reducing bacteria Desulfovibrio vulgaris (strain Miyazaki), was the first example of a heme protein exhibiting a reversible electrode reaction at a mercury electrode. Due to the sophisticated structure of proteins, there is great difficulty in most cases to achieve electron transfer of enzyme molecules via an electrode. 

In a recent report, it was shown that the reaction of cytochrome c at indium oxide OTEs exhibits an electrochemical response consistent with Butler-Volmer theory when high-quality commercial samples of cytochrome c are further purified. The electrode reaction is quasi-reversible and the CV and DCVA results of th e experiments are shown in Figure 18. These data... 

A.2.2 Solid electrodes (gold, carbon, metal oxide electrodes). Cytochrome c is also adsorbed irreversibly at solid electrodes, which mostly results in irreversible kinetices of the electrode reaction. A nearly reversible reaction of strongly adsorbed cytochrome c is, however, observed at electrodes of metal oxides (doped metal oxide semiconductor electrodes, tin-doped indium oxide electrode) [202, 203]. 

Heterogeneous electron transfer reactions between electrodes and c-type cytochromes in the bulk of solution have been extensively studied. Cytochrome c exhibits voltammetric responses ranging from reversible to kinetically irreversible at various electrodes , 71 0 electrode reactions of cytochrome cs have been found to exhibit reversible heterogeneous electron transfer at various electrodes without mediators . It has been shown that both cytochrome c and cytochrome C3 adsorb strongly on various electrode surfaces from aqueous solutions. The voltammetric behavior of these cytochromes in solution is strongly influenced by the nature of the adsorbed films on the electrode . 

V). The centers resemble PSII of chloroplasts and have a high midpoint electrode potential E° of 0.46 V. The initial electron acceptor is the Mg2+-free bacteriopheophytin (see Fig. 23-20) whose midpoint potential is -0.7 V. Electrons flow from reduced bacteriopheophytin to menaquinone or ubiquinone or both via a cytochrome bct complex, similar to that of mitochondria, then back to the reaction center P870. This is primarily a cyclic process coupled to ATP synthesis. Needed reducing equivalents can be formed by ATP-driven reverse electron transport involving electrons removed from succinate. Similarly, the purple sulfur bacteria can use electrons from H2S. 

The first reports on a reversible DET between redox proteins and electrodes were published in 1977 showing that cytochrome c is reversibly oxidized and reduced at tin-doped indium oxide [30] and gold in the presence of 4,4 -bipyridyl [31]. Only shortly after these publications appeared, papers were published describing the DET between electrode and enzyme for laccase and peroxidase [32,33]. It was observed that the overpotential for oxygen reduction at a carbon electrode was reduced by several hundred millivolts compared to the uncatalyzed reduction when laccase was adsorbed. This reaction could be inhibited by azide. The term bioelectrocatalysis was introduced for such an acceleration of the electrode process by... 

The electrode behavior of certain other cytochromes has also been investigated. It has been shown that cytochrome C3 yields a reversible wave on the mercury electrode, the reaction involving four successive transitions of... 

The effect of the 4,4 -bipyridine/gold interface on the electron transfer reactions of cytochrome c is of considerable interest. The current view pictures 4,4 -bipyridine molecules adsorbed on the gold electrode in a perpendicular, end-on orientation, forming a monolayer. Cytochrome c molecules reversibly... 

In a recent report, it was demonstrated that adsorption of 4,4 -bipyridine on platinum led to quasi-reversible rates of electron transfer with cytochrome c as evidenced by cyclic voltammetry. However, the concentration of 4,4 -bipyridine required to produce this electrochemical response was five times that which is required at gold electrodes. This difference was ascribed to the difference in the tendency of 4,4 -bipyridine to adsorb at gold and platinum electrodes. These results indicate that the use of 4,4 -bipyridine may be applicable to other solid electrodes as well for the study of cytochrome c electron transfer reactions. 

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