Properties of the solvent-stimulated ATPase activity of chloroplast coupling factor 1 from Chlamydomonas reinhardii |
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Authors: | Richard E Kneusel Sabeeha Merchant Bruce R Selman |
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Institution: | Department of Biochemistry, College of Agricultural and Life Sciences, University of Wisconsin, Madison, WI 53706 U.S.A. |
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Abstract: | The effects of solvents on the ATPase activity of chloroplast coupling factor 1 (CF1) isolated from wild-type Chlamydomonas reinhardii have been studied. Of the solvents examined, the following order summarizes their maximal ability to stimulate the ATPase activity of CF1: ethanol > methanol>allyl alcohol >n-propanol > acetone≈dioxane > ethylene glycol. Glycerol inhibits the CF1 activity at all concentrations. In the absence of organic solvents, 50% of the activity of the enzyme is irreversibly lost after a 10 min incubation at 65–70°C. Ethanol (23%) causes a 30°C drop in the temperature required for 50% inactivation. ATP partially stabilizes the CF1 in the presence, but not in the absence, of ethanol. In the absence of organic solvents, both free Mg2+ and ADP inhibit the CF1-ATPase. Mg2+ is a noncompetitive inhibitor with respect to MgATP, and the kinetic constants are: V, 6.3 μmol ATP hydrolyzed/mg protein per min; Km(MgATP), 0.23 mM; Kii(Mg2+), 27 μM; and Kis(Mg2+), 50 μM. In the presence of ethanol, double-reciprocal plots are no longer linear and have a Hill coefficient of about 1.8±0.1. V increases about 10–12-fold. The pattern of inhibition by Mg2+ appears to change from noncompetitive to competitive with respect to MgATP. In addition, ADP no longer inhibits the MgATPase activity of CF1. |
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Keywords: | Coupling factor 1 ATPase Solvent effect (C reinhardii) chloroplast coupling factor 1 Tricine To whom correspondence should be addressed |
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