Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

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 = k_exp [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, ∆H^o_≠ = 43 ± 2 kJ mol^-1 and ∆S^o_≠ = -111 ± 5 J K^-1 mol^-1. The reaction showed base catalysis and was also catalyzed by both CrO₄^2- and acrylamide. It was inhibited by the oxidants WO₄^2-, MoO₄^2-, 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).

Keywords: Cytochrome c; Hydrogen peroxide; Hydroxyl radicals; Kinetics; Mechanism; Proteins; Oxidative degradation; UV-VIS spectroscopy.

References: 64 live references.