Inhibition of ATPase activity by vanadate, having K1 2of 0.5 mM, was demonstrated in the CF1-ATPase. The Ca2+-dependent ATPase activity of the isolated enzyme was inhibited in an allosteric manner by vanadate with a Hill coefficient of 3.19 ± 0.6. Vanadate also inhibited ATPase and Pi-ATP exchange activities of the chloroplast membrane-bound enzyme. Using51V NMR it was demonstrated that ATP caused partial release of about 1.87 equivalents while ADP caused additional binding of approximately 1.46 equivalents of vanadate, when added to a solution containing CF1equilibrated with vanadate. The relevance of these results to a possible involvement of a pentacovalent phosphate as transition state intermediate in the hydrolysis of ATP by CF1-ATPase is discussed. © 1992.
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