Application of Promoter Modified Electrodes to Bioelectrochemical Measurements on the Effects of Origin and Modification of Lysine Residues of Cytochrome c

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Abstract
Using promoter-modified electrodes, electron-transfer reactions of cytochrome c at an electrode and with cytochrome c oxidase were examined. The electrochemical behavior of cytochromes c from horse, bovine, chicken and tuna hearts at an electrode was similar to each other. Little difference was observed for the reactions between cytochromes c of various origins and cytochrome c oxidase from bovine in a phosphate buffer solution. Also, when a few (less than three) lysine residues of cytochrome c were treated with 4-chloro-3, 5-dinitrobenzoic acid (CDNP) or 2, 4-dinitrofluorobenzene (DNP), the electrode reaction of the modified (especially, mono-substituted) cytochrome c still showed no significant difference from that of the native one. On the other hand, the electron-transfer reaction between CDNP- or DNP-substituted cytochrome c at lysine 13 and/or 72 and cytochrome c oxidase was greatly affected, even when only one or two lysine residues of cytochrome c were modified. Since the cytochrome c molecules of different origins examined have about 3-19 differences in their amino acid sequences, but most lysine residues remain invariant, the present results indicate that lysine residues of cytochrome c play an important role in the interaction with cytochrome c oxidase; however, the promoter modified electrode surface does not recognize cytochrome c molecule very rigorously. The present study also shows that electrochemical techniques with the aid of functional electrodes are applicable as useful, convenient methods to analyze the biological reactions of proteins