Regulation in vitro of rat liver pyruvate kinase by phosphorylation-dephosphorylation reactions, catalyzed by cyclic-AMP dependent protein kinases and a histone phosphatase.

1. Cyclic-AMP dependent protein kinases, resolved by chromatography on DEAE-cellulose and hydroxylapatite, catalysed the phosphorylation of rat liver pyruvate kinase and calf thymus histones by [gamma32P]ATP. [32P]phosphopeptides, from acid hydrolysates of pyruvate kinase phosphorylated by the different protein kinase fractions, displayed identical electrophoretic patterns. Phosphorylation inhibited pyruvate kinase activity. 2. Full activity was restored when phosphorylated pyruvate kinase was dephosphorylated by a histone phosphatase from the soluble fraction of rat liver. These results are consistent with the hypothesis that pyruvate kinase is regulated by phosphorylation-dephosphorylation reactions.