Catalytic intermediates of cytochrome bd terminal oxidase at steady-state: ferryl and oxy-ferrous species dominate.

Abstract : The cytochrome bd ubiquinol oxidase from Escherichia coli couples the exergonic two-electron oxidation of ubiquinol and four-electron reduction of O(2) to 2H(2)O to proton motive force generation by transmembrane charge separation. The oxidase contains two b-type hemes (b(558) and b(595)) and one heme d, where O(2) is captured and converted to water through sequential formation of a few intermediates. The spectral features of the isolated cytochrome bd at steady-state have been examined by stopped-flow multiwavelength absorption spectroscopy. Under turnover conditions, sustained by O(2) and dithiothreitol (DTT)-reduced ubiquinone, the ferryl and oxy-ferrous species are the mostly populated catalytic intermediates, with a residual minor fraction of the enzyme containing ferric heme d and possibly one electron on heme b(558). These findings are unprecedented and differ from those obtained with mammalian cytochrome c oxidase, in which the oxygen intermediates were not found to be populated at detectable levels under similar conditions [M.G. Mason, P. Nicholls, C.E. Cooper, The steady-state mechanism of cytochrome c oxidase: redox interactions between metal centres, Biochem. J. 422 (2009) 237-246]. The data on cytochrome bd are consistent with the observation that the purified enzyme has the heme d mainly in stable oxy-ferrous and ferryl states. The results are here discussed in the light of previously proposed models of the catalytic cycle of cytochrome bd.
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Vitaliy B Borisov, Elena Forte, Paolo Sarti, Alessandro Giuffrè. Catalytic intermediates of cytochrome bd terminal oxidase at steady-state: ferryl and oxy-ferrous species dominate.. Biochimica et Biophysica Acta (BBA) - Enzymology, Elsevier, 2011, 1807 (5), pp.503-9. ⟨10.1016/j.bbabio.2011.02.007⟩. ⟨pasteur-00975925⟩

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