title: Facilitated intramolecular electron transfer in cytochrome bo-type ubiquinol oxidase initiated upon reaction of the fully reduced enzyme with dioxygen.
abstract: Flow-flash and double-flash studies of the reaction of fully reduced bo-type quinol oxidase with oxygen have revealed that a single turnover of the enzyme proceeds much faster than mammalian cytochrome c oxidase. Facilitated intramolecular electron transfer in the bo-type oxidase with k > 5 x 10(4) s-1 at pH 7.4 and 20 degrees C is responsible for this fast turnover. The kinetics of this reaction indicates that the oxygen reduction does not require electron exchange between quinol oxidase molecules, each having three metal centers. Thus, a bound quinol in the fully reduced enzyme is suggested to be an electron source for complete reduction of dioxygen into water supplementing electrons provided by the metal centers. A single turnover of the quinol oxidase yields a novel spectral species with a Soret maximum at 415 nm corresponding to a 'pulsed' state of mammalian cytochrome c oxidase.
authors.affiliation: Department of Public Health, Faculty of Medicine, Kyoto University, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Orii
authors.forename: T
authors.initials: T
authors.lastname: Mogi
authors.forename: M
authors.initials: M
authors.lastname: Kawasaki
authors.forename: Y
authors.initials: Y
authors.lastname: Anraku
mesh_terms: D000818:Animals; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000378:metabolism*; D007700:Kinetics; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D013053:Spectrophotometry / Q000379:methods
chemical_list: C038862:cytochrome o oxidase; D003576:Electron Transport Complex IV; D010100:Oxygen