The regulation of pyruvate kinase in the hepatopancreas of Carcinus maenas)

1. Estimation of the activity of pyruvate kinase and pyruvate carboxylase in the hepatopancreas of Carcinus maenas gave values of 28.5 and 7.4 units/g wet wt tissue respectively. 2. The concentrations of substrates, products and allosteric effectors of these enzymes in hepatopancreas were measured. 3. The activities of pyruvate kinase and pyruvate carboxylase were redetermined using the approximate physiological range of substrate and effectors. 4. Under these conditions the effective activity of pyruvate kinase could be decreased to less than 2 units/g wet wt tissue whereas that for the pyruvate carboxylase was 2.6 units/g wet wt tissue indicating that a net synthesis of phosphoenolpyruvate could occur in vivo.