Cytochrome c oxidase binding of hydrogen peroxide

Abstract

Oxidized cytochrome c oxidase can bind H2O2, as evidenced by changes in its spectrum and its ability to use H2O2 as an electron acceptor in cytochrome c oxidation. The affinity of the oxidized enzyme for H2O2 is high, with a Kd of < 10 .mu.M, and the binding is inhibited by ligands of cytochrome a3. Oxidized cytochrome c oxidase, in [beef heart] submitochondrial particles or solubilized in several ionic and nonionic detergents, binds peroxide with comparable affinities. The size of the spectral shift observed upon peroxide binding depends on the pH of the solution and differs in extinction coefficient between preparations, but all preparations tested appeared to bind peroxide. The differences in the magnitude of the spectral shift upon peroxide binding to different preparations suggest that oxidized cytochrome c oxidase as prepared may be made up of more than 1 species and that the proportion of the species which binds peroxide varies with the preparation. These studies of the binding of peroxide clarify the mechanism by which cytochrome c oxidase catalyzes the reduction of O2 to water without the formation of free-radical intermediates.