Role of a bound ubiquinone on reactions of the Escherichia coli cytochrome bo with ubiquinol and dioxygen

FEBS Letters

Mogi, Tatsushi¹  Sato-Watanabe, Mariko¹  Orii, Yutaka²  Miyoshi, Hideto³ 

[1] Department of Biological Sciences, Graduate School of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan;Department of Public Health, Graduate School of Medicine, Kyoto University, Sakyo-ku, Kyoto 606-8315, Japan;Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan

关键词: Bound quinone;    Cytochrome bo;    Quinol oxidase;    Time-resolved visible spectroscopy;    Escherichia coli;    ΔUbiA;    cytochrome bo isolated from a ubiquinone-deficient mutant;    ΔUbiA/PC32;    ΔUbiA reconstituted with PC32;    Q n;    ubiquinone-n;    Q n H2;    ubiquinol-n;    QH;    the high-affinity quinone binding site;    QL;    the low-affinity quinol oxidation site;    PC32;    2;    6-dibromo-4-cyanophenol;   

DOI  :  10.1016/S0014-5793(99)01047-9

学科分类：生物化学/生物物理

来源: John Wiley & Sons Ltd.

【 摘 要 】

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 (ΔUbiA) 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 ∼1×10⁴ 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.

【 授权许可】

Unknown