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  • Title: Role of a bound ubiquinone on reactions of the Escherichia coli cytochrome bo with ubiquinol and dioxygen.
    Author: Mogi T, Sato-Watanabe M, Miyoshi H, Orii Y.
    Journal: FEBS Lett; 1999 Aug 27; 457(2):223-6. PubMed ID: 10471783.
    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.
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