The effect of pH,ubiquinone depletion and myxothiazol on the reduction kinetics of the prosthetic groups of ubiquinol: Cytochrome c oxidoreductase |
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Authors: | Simon De Vries Simon P.J. Albracht Jan A. Berden Carla A.M. Marres E.C. Slater |
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Affiliation: | Laboratory of Biochemistry, B.C.P. Jansen Institute, University of Amsterdam, P.O. Box 20151, 1000 HD Amsterdam The Netherlands |
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Abstract: | (1) The kinetics of the reduction by duroquinol of the prosthetic groups of QH2: cytochrome c oxidoreductase and of the formation of ubisemiquinone have been studied using a combination of the freeze-quench technique, low-temperature diffuse-reflectance spectroscopy, EPR and stopped flow. (2) The formation of the antimycin-sensitive ubisemiquinone anion parallels the reduction of both high-potential and low-potential cytochrome b-562. (3) The rates of reduction of both the [2Fe-2S] clusters and cytochromes (c + c1) are pH dependent. There is, however, a pH-dependent discrepancy between their rate of reduction, which can be correlated with the difference in pH dependencies of their midpoint potentials. (4) Lowering the pH or the Q content results in a slower reduction of part of the [2Fe-2S] clusters. It is suggested that one cluster is reduced by a quinol/semiquinone couple and the other by a semiquinone/quinone couple. (5) Myxothiazol inhibits the reduction of the [2Fe-2S] clusters, cytochrome c1 and high-potential cytochrome b-562. (6) The results are consistent with a Q-cycle model describing the pathway of electrons through a dimeric QH2: cytochrome c oxidoreductase. |
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Keywords: | Ubiquinol ESR Myxothiazol Reduction kinetics Electron transfer Semiquinone duroquinol ubisemiquinone anion durosemiquinone anion BAL British Anti-Lewisite (2,3-dimercaptopropanol) Mops 4-morpholinepropane-sulphonic acid |
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