Enzymic redox reactions of cytochromes c

The two cytochromes c for which detailed tertiary structures have been obtained recently—cytochrome c from mammalian mitochondria and cytochrome c₂ from Rhodospirillum rubrum—have been compared in reactivity in the physiologic redox systems for which the former is the natural substrate. These systems are the mitochondrial DPNH-cytochrome c reductase (complex I–III) and cytochrome c oxidase (complex IV). In addition, the effects of antimycin A (a specific inhibitor in the reductase system) and L-polylysine (usually employed to inhibit the oxidase system) on the reduction and oxidation of cytochromes c and c₂ have been studied. Preliminary data for these two cytochromes, as well as for five others representative of different classes of bacterial and algal cytochrome c are presented. Implications of these findings for current attempts to rationalize the structural features of cytochromes c are considered.