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Interaction of phenylglyoxal with the human erythrocyte (Ca2+ + Mg2+)- ATPase. Evidence for the presence of an essential arginyl residue

BU Raess, DM Record and G Tunnicliff

Incubation of human erythrocyte membranes with phenylglyoxal irreversibly inhibited (Ca2+ + Mg2+)-ATPase activity in a pseudo-first order manner, but followed overall second order kinetics. The enzyme exhibited a low affinity ATP-binding site with a Km of approximately 125 microM. The effects of the inhibitor could be markedly diminished if ATP was also present during phenylglyoxalation. This indicated that phenylglyoxal and ATP were binding at the same site on the enzyme. The concentration-dependent inactivation reduced both the Vmax and the Km of the enzyme, but did not change the apparent affinity for Ca2+. Because ATP could protect against inactivation in the absence of Ca2+ and Mg2+, we suggest that free ATP can bind at the low affinity site. The modified enzyme was still capable of being activated by calmodulin. Our data indicate that only the ATP site was affected by the inhibitor, whereas the Ca2+ sites were not. Since it is established that phenylglyoxal can react with arginyl residues, we conclude that the binding of the ATP to the low affinity site on the human erythrocyte (Ca2+ + Mg2+)-ATPase involves such a residue.

Volume 27, Issue 4, pp. 444-450, 04/01/1985
Copyright © 1985 by American Society for Pharmacology and Experimental Therapeutics




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Copyright © 1985 by the American Society for Pharmacology and Experimental Therapeutics