The Regulation of Pyruvate Kinase of Escherichia coli by Fructose Diphosphate and Adenylic Acid

The regulatory properties of pyruvate kinase from Escherichia coli were investigated. Both fructose 1,6-diphosphate and AMP were found to activate the enzyme. These two positive effectors, however, had fundamentally different effects on the sigmoidal plots of rate-concentration data with P-enolpyruvate as the variable substrate. While fructose-1,6-di-P changed the Vmax but not the sigmoidality of the rate-concentration curves, AMP only changed the Km and converted the sigmoidal plot into a hyperbola. The enzyme lost its activity on storage at 4° but could be reactivated by dithiothreitol by a time-dependent process. Sucrose density gradient centrifugation revealed that dithiothreitol caused a dimerization of the enzyme.