title: Ferricytochrome c induces monophasic kinetics of ferrocytochrome c oxidation in cytochrome c oxidase.
abstract: The kinetics of ferrocytochrome c oxidation by reconstituted cytochrome c oxidase (COX) from bovine heart was followed by a spectrophotometric method, using on-line data collection and subsequent calculation of reaction rates from a function fitted to the progress curve. When reaction rates were calculated at increasing reaction times, the multiphasic kinetics of ferrocytochrome c oxidation gradually changed into monophasic Michaelis-Menten kinetics. The same phenomenon was observed when ferrocytochrome c oxidation was followed in the presence of increasing amounts of ferricytochrome c. From these results we conclude that ferricytochrome c shifts the multiphasic kinetics of ferrocytochrome c oxidation by COX into monophasic kinetics, comparable to high ionic strength conditions. Furthermore, we show that ferricytochrome c inhibits the "high affinity phase" of ferrocytochrome c oxidation in an apparently competitive way, while inhibition of the "low affinity phase" is noncompetitive. These findings are consistent with a "regulatory site model" where both the catalytic and the regulatory site bind ferro- as well as ferricytochrome c.
authors.affiliation: Fachbereich Chemie (Biochemie), Philipps-Universität, Marburg, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Reimann
authors.forename: K H
authors.initials: KH
authors.lastname: Röhm
authors.forename: B
authors.initials: B
authors.lastname: Kadenbach
mesh_terms: D000818:Animals; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002417:Cattle; D003574:Cytochrome c Group / Q000378:metabolism* / Q000494:pharmacology*; D003576:Electron Transport Complex IV / Q000378:metabolism*; D007700:Kinetics; D008929:Mitochondria, Heart / Q000201:enzymology; D010084:Oxidation-Reduction; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D003574:Cytochrome c Group; D014634:Valinomycin; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D003576:Electron Transport Complex IV