title: Effect of pH on the steady state kinetics of bovine heart NADH: coenzyme Q oxidoreductase.
abstract: Complete initial steady state kinetics of NADH-decylubiquinone (DQ) oxidoreductase reaction between pH 6.5 and 9.0 show an ordered sequential mechanism in which the order of substrate bindings and product releases is NADH-DQ-DQH2-NAD+. NADH binding to the free enzyme is accelerated by protonation of an amino acid (possibly a histidine) residue. The NADH release is negligibly slow under the turnover conditions. The rate of DQ binding to the NADH-bound enzyme and the maximal rate at the saturating concentrations of the two substrates, which is determined by the rates of DQH2 formation in the active site and releases of DQH2 and NAD+ from the enzyme, are insensitive to pH, in contrast to clear pH dependencies of the maximal rates of cytochrome c oxidase and cytochrome bc1 complex. Physiological significances of these results are discussed.
authors.affiliation: Department of Life Science, Himeji Institute of Technology, Kamigohri Akoh Hyougo 678-1297, Japan.
authors.forename: Nobuko
authors.initials: N
authors.lastname: Hano
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Nakashima
authors.forename: Kyoko
authors.initials: K
authors.lastname: Shinzawa-Itoh
authors.forename: Hirohito
authors.initials: H
authors.lastname: Terada
authors.forename: Shinya
authors.initials: S
authors.lastname: Yoshikawa
mesh_terms: D000818:Animals; D002417:Cattle; D014450:Electron Transport Complex III / Q000378:metabolism*; D003576:Electron Transport Complex IV / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009206:Myocardium / Q000201:enzymology*; D009245:NADH Dehydrogenase / Q000378:metabolism*; D010084:Oxidation-Reduction; D011485:Protein Binding; D013379:Substrate Specificity; D014451:Ubiquinone / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D014451:Ubiquinone; C060262:2,3-dimethoxy-5-methyl-6-decyl-1,4-benzoquinone; D009245:NADH Dehydrogenase; D003576:Electron Transport Complex IV; D014450:Electron Transport Complex III