ELECTROCHEMICAL BEHAVIOR OF CYTOCHROME-C3 OF DESULFOVIBRIO-VULGARIS, STRAIN MIYAZAKI, ON THE MERCURY-ELECTRODE

Potentiometric, pulse polarographic, and cyclic voltammetric techniques were used to investigate the electrochemical behavior of cytochrome c3 of Desulfovibrio vulgaris, strain Miyazaki, on mercury electrode. The electrode reaction of cytochrome c3, which contains four hemes in the molecule, is reversible and diffusion controlled with a diffusion coefficient of 0.94 X 10-6 cm2 s-1 for the ferri form and 0.71 X 10-6 cm2 s-1 for the ferro form. The formal potential of the ferri- and ferrocytochrome c3 couple is -0.528 V (-0.287 V vs. NHE) and the polarographic half-wave potential is -0.527 V. The electrode reaction rate constant of cytochrome c3 is too fast to be measured by the present electrochemical methods. It is estimated to be 0.1 cm s-1 or greater. A large Nernst slope and broad voltammograms with smaller peak current than expected from a four-electron process suggested that the electrode reactions of cytochrome c3 are four one-electron processes and the hemes in the molecule are nonequivalent and noninteracting. The spacings between the standard potentials of the adjacent hemes are about -50, -20, and -40 mV, respectively. © 1979, American Chemical Society. All rights reserved.