کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
1942814 | 1052631 | 2011 | 7 صفحه PDF | دانلود رایگان |

The cytochrome bd ubiquinol oxidase from Escherichia coli couples the exergonic two-electron oxidation of ubiquinol and four-electron reduction of O2 to 2H2O to proton motive force generation by transmembrane charge separation. The oxidase contains two b-type hemes (b558 and b595) and one heme d, where O2 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 O2 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 b558. 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.
Research highlights
► Spectral features of cytochrome bd terminal oxidase examined at steady-state by time-resolved spectrophotometry
► Ferryl and oxy-ferrous catalytic intermediates dominate
► Model of the catalytic cycle proposed.
Journal: Biochimica et Biophysica Acta (BBA) - Bioenergetics - Volume 1807, Issue 5, May 2011, Pages 503–509