A kinetic study of the cytochrome c-hydrogen peroxide reaction

The kinetics of the reaction of cytochrome c with H2O2 was studied in aqueous phosphate media near physiological pH (5.7 - 7.2). The UV-VIS spectra indicated that the heme prosthetic group of the protein suffered an oxidative degradation during the reaction. The experimental rate law was v = kexp [cytochrome c] [H2O2], with k(exp) = (A + B [H+])/(1 + C [H+]). The apparent activation parameters associated with k(exp) were E-a = 46 +/- 2 kJ mol(-1), Delta H-not equal(o) = 43 +/- 2 kJ mol(-1) and Delta S-not equal(o) = - 111 +/- 5 J K-1 mol(-1). The reaction showed base catalysis and was also catalyzed by both CrO42- and acrylamide. It was inhibited by the oxidants WO42-, MoO42-, VO3- and [Fe(CN)(6)](3-) as well as by the reductants [Fe(CN)(6)](4-) and D-mannitol, whereas Zn2+ and superoxide dismutase had no appreciable effect. The results are consistent with initial reduction of iron from Fe(III) to Fe(II) ( supported by inhibition caused by most oxidants), followed by a hydroxyl-radical mediated oxidative degradation of the heme prosthetic group ( supported by the inhibition caused by both [Fe(CN)(6)](4-) and D-mannitol).