title: Facilitated intramolecular electron transfer in the Escherichia coli bo-type ubiquinol oxidase requires chloride.
abstract: Previous flow-flash measurements using the bo-type ubiquinol oxidase of Escherichia coli have revealed that facilitated heme B-heme O intramolecular electron transfer initiated upon reaction of the fully-reduced enzyme with dioxygen proceeds with a rate constant higher than 5 x 10(4) s-1 at pH 7.4 and 20 degrees C. Depletion of chloride anions from the enzyme by HPLC performed in the present study considerably decreased the rate constant to approximately 700 s-1, but the reaction of either dioxygen or carbon monoxide at the binuclear center was not affected at all kinetically. These results strongly suggest that Cl- is essential in maintaining a subtle molecular structure around the heme B and heme O that enables facilitated intramolecular electron transfer. Furthermore, a series of absorption spectra of the enzyme collected on time scales from microseconds to milliseconds during its single turnover indicate that as heme-heme intramolecular electron transfer is retarded by depletion of Cl-, an alternative electron transfer pathway is invoked. We discuss a possible role of novel bound Cl- in electron transfer from bound quinol to the binuclear center to accomplish dioxygen reduction.
authors: Department of Public Health, Faculty of Medicine, Kyoto University, Japan.
authors: Y
authors: Y
authors: Orii
authors: T
authors: T
authors: Mogi
authors: M
authors: M
authors: Sato-Watanabe
authors: T
authors: T
authors: Hirano
authors: Y
authors: Y
authors: Anraku
mesh_terms: D002248:Carbon Monoxide / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism*; D003573:Cytochrome b Group; D003580:Cytochromes / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D007700:Kinetics; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D013057:Spectrum Analysis
chemical_list: D002712:Chlorides; D003573:Cytochrome b Group; D003580:Cytochromes; D029968:Escherichia coli Proteins; D002248:Carbon Monoxide; C017168:cytochrome bo, E coli; D010088:Oxidoreductases; C020094:duroquinol oxidase; D010100:Oxygen