REGULATION OF LIVER PYRUVATE KINASE BY PHOSPHORYLATION-DEPHOSPHORYLATION REACTIONS

Abstract

This chapter elaborates the regulation of liver pyruvate kinase by phosphorylation–dephosphorylation reactions. Pyruvate kinase was purified from rat and pig liver, and found to be a substrate for cAMP-stimulated protein kinase from the same source. Maximally, one mol of phosphate could be bound to one mol of subunit of the tetrameric enzyme. The isolation and analysis of the amino acid sequence of one single peptic peptide from each of the rat, and pig enzymes shows that a specific seryl residue in the enzyme is phosphorylated. The amino acid sequences at the phosphorylated sites have been found to be -Leu-Arg-Arg-Ala-SerP-Val-Ala-, and -Leu-Arg-Arg-Ala-SerP-Leu- in the rat, and pig enzymes, respectively. The sequences are similar to those of most other substrates of cAMP-stimulated protein kinase, with two arginyl residues preceding the seryl residue, and with at least one neutral amino acid residue nearest the serine on each side. That the phosphorylation of liver pyruvate kinase is a specific reaction and is further supported by the fact that neither pyruvate kinase type M from pig muscle nor type A from pig kidney is phosphorylated by cAMP-stimulated protein kinase.