Heat stabilization dependence on redox state of cytochrome cd1 oxidase from Pseudomonas aeruginosa |
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Authors: | S Mitra J W Donovan R Bersohn |
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Affiliation: | 1. Department of Chemistry, Columbia University, New York, N.Y. 10027 USA;2. Western Regional Research Center, SEA, U.S. Department of Agriculture, Berkeley, CA 94710 USA |
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Abstract: | The irreversible thermal denaturation of cytochrome cd1 oxidase from as a function of the oxidation-reduction states of its hemes was observed with a differential scanning calorimeter. Upon full reduction of the four hemes, the apparent denaturation temperature decreases by about 10° and the denaturation enthalpy decreases slightly: oxidized, 5.9 cal/gm; reduced, 5.4 cal/gm. At pH 7.5, the first order rate constants for denaturation at 90°C are: reduced, 33 × 10?3s?1; oxidized, 3 × 10?3s?1. Thus, oxidation of the hemes reuults in heat stabilization of the cytochrome oxidase. The activation energy for denaturation of fully reduced oxidase, 53 kcal/mol, is less than that for fully oxidized protein (73 kcal/mol). |
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