PRODUCTION OF REACTIVE OXYGEN-DERIVED SPECIES BY REDOX REACTIONS BETWEEN FE(II)CYTOCHROME-C AND OXYGEN - A KINETIC-STUDY

In aerated water solutions Fe(II)Cytochrome c is slowly oxidized to Fe (III)Cytochrome c by molecular oxygen, from which superoxide anion rad icals are produced (k(obs) = 2.7x10(-4) min(-1) at 37 degrees C and pH = 7.3). The biological importance of this reaction has been evidenced by kinetic investigations in the presence of scavengers. In the prese nce of Superoxide dismutase the oxidation rate is strongly enhanced (k (obs) = 3x10(-3) min(-1) at 37 degrees C). Catalase and mannitol reduc e the rate constant values by 50% and 25% respectively either in the p resence or in the absence of Superoxide dismutase: differences between rate constants correspond to the differences in stoichiometric redox ratios indicating that hydrogen peroxide and hydroxyl radicals are for med subsequently to the production of superoxide anion radicals.