Kinetic Studies of the Inhibition of Muscle Phosphorylase Phosphatase

Abstract

Abstract Inorganic phosphate, glucose 1-phosphate, divalent metal ions, EDTA, m-propoxybenzamidine, and AMP were found to be competitive inhibitors of the reaction catalyzed by phosphorylase phosphatase. By a comparison of kinetic studies with the substrates, phosphorylase a and the phosphorylated peptide, it was deduced that inorganic phosphate affected the reaction by binding to the catalyst, whereas glucose-1-P inhibited by binding to the substrate, phosphorylase. Inhibition by divalent metal ions and m-propoxybenzamidine was explained by binding to a single site on phosphorylase phosphatase. This site is presumed to be the one that interacts with the arginyl function of the substrate. EDTA inhibition appears to occur at a different locus on the phosphatase. AMP changes the phosphatase reaction by binding to phosphorylase a. The phosphorylase a-AMP complex is poorly recognized, if at all, by phosphorylase phosphatase.