Conformations of cytochromes c3 from Desulfovibrio vulgaris, Miyazaki and Hildenborough strains, and from Desulfovibrio desulfuricans, Norway strain, adsorbed on silver electrode are investigated by using voltammetric and surface-enhanced Raman scattering spectroscopic techniques. The voltammetric measurements reveal that the redox properties of cytochromes c3 in the bulk are well preserved in the adsorbed cytochromes. That is, the formal potentials of the hemes in the adsorbed species are almost the same as those of the bulk species. On the other hand, the redox potential of the adsorbed cytochromes c3 monitored by SERS corresponds to the most positive redox site among the four hemes in the molecule. This is probably due to the fact that cytochromes c3 are specifically adsorbed on silver electrode through the lysine residues surrounding heme-1, which is responsible for SERS. These results also suggest that heme-1 in cytochromes c3 is the most positive redox site in the molecule.

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