title: Role of a bound ubiquinone on reactions of the Escherichia coli cytochrome bo with ubiquinol and dioxygen.
abstract: To probe the functional role of a bound ubiquinone-8 in cytochrome bo-type ubiquinol oxidase from Escherichia coli, we examined reactions with ubiquinol-1 and dioxygen. Stopped-flow studies showed that anaerobic reduction of the wild-type and the bound ubiquinone-free (DeltaUbiA) enzymes with ubiquinol-1 immediately takes place with four kinetic phases. Replacement of the bound ubiquinone with 2,6-dibromo-4-cyanophenol (PC32) suppressed the anaerobic reduction of the hemes with ubiquinol-1 by eliminating the fast phase. Flow-flash studies in the reaction of the fully reduced enzyme with dioxygen showed that the heme b-to-heme o electron transfer occurs with a rate constant of approximately 1x10(4) s(-1) in all three preparations. These results support our previous proposal that the bound ubiquinone is involved in facile oxidation of substrates in subunit II and subsequent intramolecular electron transfer to low-spin heme b in subunit I.
authors.affiliation: Department of Biological Sciences, Graduate School of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo, Japan. mogi@biol.s.u- tokyo.ac.jp
authors.forename: T
authors.initials: T
authors.lastname: Mogi
authors.forename: M
authors.initials: M
authors.lastname: Sato-Watanabe
authors.forename: H
authors.initials: H
authors.lastname: Miyoshi
authors.forename: Y
authors.initials: Y
authors.lastname: Orii
mesh_terms: D003573:Cytochrome b Group; D003580:Cytochromes / Q000378:metabolism*; D004579:Electron Transport; D004926:Escherichia coli / Q000201:enzymology / Q000378:metabolism*; D029968:Escherichia coli Proteins; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D014451:Ubiquinone / Q000031:analogs & derivatives* / Q000378:metabolism*
chemical_list: D003573:Cytochrome b Group; D003580:Cytochromes; D029968:Escherichia coli Proteins; D014451:Ubiquinone; C017168:cytochrome bo, E coli; C003741:ubiquinol; D010100:Oxygen