title: The cytochrome c peroxidase activity of cytochrome oxidase.
abstract: I have found that mammalian cytochrome oxidase catalyzes the peroxidatic oxidation of ferrocytochrome c under strictly anaerobic conditions. An apparent Km value for ferrocytochrome c was 2 microM, and a second order rate constant, estimated as an extrapolated value, was 1.4 X 10(6) M-1 s-1 at pH 7.4 at 25 degrees C. These values were quite similar to the corresponding values of 6.4 microM and 1.9 X 10(6) M-1 s-1 determined for the intrinsic oxidase activity. The rate of the peroxidatic oxidation showed a hyperbolic dependence on the concentration of hydrogen peroxide, and the apparent Km value ws 0.18 mM. Cyanide and azide at 0.1 mM inhibited the peroxidase activity by 100 and 98%, respectively, whereas, under carbon monoxide at 750 mm Hg, 10% of the activity still remained. Under air, cytochrome oxidase acted simultaneously as oxidase and peroxidase.
mesh_terms: D000818:Animals; D002417:Cattle; D003574:Cytochrome c Group / Q000378:metabolism; D003578:Cytochrome-c Peroxidase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D003576:Electron Transport Complex IV / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000378:metabolism; D007700:Kinetics; D010100:Oxygen / Q000494:pharmacology; D010544:Peroxidases / Q000378:metabolism*
chemical_list: D003574:Cytochrome c Group; D006861:Hydrogen Peroxide; D010544:Peroxidases; D003578:Cytochrome-c Peroxidase; D003576:Electron Transport Complex IV; D010100:Oxygen