Preliminary studies have shown that epinephrine inhibits pyruvate kinase in rat hepatocytes by alpha-adrenergic mediated mechanisms. Measurements of c-AMP levels will be made to determine if these alpha-mechanisms represent c-AMP independent regulation of the enzyme. Studies in progress concerning the phosphorylation of pyruvate kinase by glucagon and epinephrine in the rat hepatocyte will also be completed. We have identified a 35,000 - 37,000 dalton phosphorylated protein subunit which can be isolated from hepatocytes by apparently a monospecific antibody against pyruvate kinase (60,000 dalton subunits). The nature of the 35,000 dalton protein and its relationship to pyruvate kinase will be investigated. Finally, in vitro studies concerning isolation and characterization of enzymes involved in phosphorylation and dephosphorylation of pyruvate kinase will be initiated. The c-AMP dependent (or independent) protein kinases and pyruvate kinase phosphatases will be isolated from rat hepatocytes to identify those enzymes directly responsible for the particular type L pyruvate kinase isozyme.