Cytochrome promoted electrode response

The involvement of lysine amino acid residues on cytochrome c in the heterogeneous reactions with functionalized electrodes seems to have been established. Importantly, it is now thought that the proposed protein-promoter complex is more likely to be dynamic, as revealed by the results of a recent investigation (28) of site-specific 4-chloro-3,5-dinitrophenyl (CDNP)-substituted cytochrome c. It was found that monosubstitution of either Lys 13 or Lys 72 did not result in any significant change in its electrochemical response, whereas two modifications greatly decreased the heterogeneous rate constant, and complete loss of electrochemical activity was observed upon modification of more lysines. It was proposed that the electrode reaction occurred in numerous rotational conformations. Therefore, for the mono-... 

However, addition of cytochrome c to a solution of either cytochrome is or plastocyanin promoted 41, 42) the electrochemistry of the latter at the electrodes with which they do not normally interact (Fig. 5C). That the observed response was direct and not mediated was shown using the redox-inactive protein zinc(II)-cytochrome c, instead of iron(III)-cytochrome c (Fig. 5D and E). Similarly, direct electrochemical response of cytochrome c was obtained 43) at an unfavorable electrode by the promotion of either cytochrome 65 or plastocyanin. 

Taniguchi, I., Iseki, M., Toyosawa, K., Yamaguchi, H., Yasokouchi, K., Purines as New Promoters for the Voltammetric Response of Horse Heart Cytochrome C at Gold Electrodes , J. Electroanal. Chem. 164 (1984) 385-391. 

It has been shown [103] that cytochrome c exhibits different voltam-metric responses depending on the nature of the electrode surface. Various surface modifiers have been proposed to facilitate electron transfer to or from some conjugated proteins. The SERS spectroscopy has been used to elucidate the interfacial properties of cytochrome c in the presence of the promoters at both silver and gold electrodes [103, 106]. It has been demonstrated that the surface modifiers act either as the surface active agents with which cytochrome c is coadsorbed on the electrode, or they form a strongly adsorbed layer through which the electron exchange process between the native form of cytochrome c and the electrode takes place. 

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