Conformational transitions in the regulation of cytochrome c oxidase activity |
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| Affiliation: | 1. Department of Physics, City College of New York, 160 Convent Avenue, New York, NY 10031, USA;2. Department of Physics, Graduate Center, City University of New York, 365 Fifth Avenue, New York, NY 10016, USA;3. Department of Chemistry and Theoretical Chemistry Institute, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI 53706, USA |
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| Abstract: | Oxidation of cytochrome c, catalyzed by cytochrome oxidase embedded in artificial liposomes of high respiratory control ratio (between 5 and 9.5), has been studied by rapid mixing techniques, under which conditions the enzyme undergoes a limited number of turnovers (from 1 to 5). The time course of the reaction could be satisfactorily simulated by a procedure derived from the concerted two-state model of Monod-Wyman-Changeux.The bulk of data and the novel analytical approach confirm the proposal that cytochrome oxidase undergoes a transition from a fast-reacting to a slow-reacting form as a consequence of the electrochemical gradient built up across the phospholipidic bilayer, and substantiate the idea that the conformational change: - •occurs as an all-or-none process after about one turnover irrespective of the molar ratio between substrate and enzyme, and
- •is not immediately correlated to the other well known transition from the resting to the pulsed form of the enzyme.
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