The antioxidant functions of cytochrome c

Low (C-1/2 = 1.5 x 10(-7) M) concentrations of horse cytochrome c strongly inhibit H2O2 production by rat heart mitochondria under conditions of reverse electron transfer from succinate to NAD(+). The effect is abolished by binding of cytochrome c with liposomes and is not prevented by SOD. Yeast cytochrome c is much less effective than the horse protein whereas acetylated horse cytochrome c is without effect. H2O2 formation stimulated by antimycin A is resistant to added cytochrome c. In inside-out submitochondrial vesicles, H2O2 production is suppressed by all three cytochrome c samples tested, but at higher concentrations (C-1/2 is about 5 x 10(-7) M). In vesicles, SOD abolishes the cytochrome c inhibition. We conclude that extramitochondrial cytochrome c is competent in down-regulation of the Complex I H2O2 production linked to the reverse electron transfer. Such an effect is absent in the inside-out submitochondrial vesicles where another antioxidant cytochrome c function can be observed ed, i.e. the oxidation of O-2(-.) to O-2 A possible role of cytochrome c in the antiosidant defence is discussed. (C) 1999 Federation of European Biochemical Societies.