The Regulation of Liver Pyruvate Kinase by Phosphorylation—Dephosphorylation

Abstract

Publisher Summary This chapter discusses the regulation of liver pyruvate kinase by phosphorylation–dephosphorylation. The rate and extent of the phosphorylation of L-type liver pyruvate kinase in vitro indicate that it is a specific reaction. This is supported by inhibition of the enzyme by the phosphorylation, which may be expected with regard to the known effect of cAMP on liver gluconeogenesis. The specificity of the phosphorylation reaction is also demonstrated by the fact that neither the A-type enzyme from pig kidney nor the M-type muscle enzyme from the rabbit or pig are substrates of cAMP-stimulated protein kinase. However, phosphorylation of the type-A enzyme from chicken liver has been preliminarily reported. The phosphorylation of liver pyruvate kinase in vitro is reversible, owing to the presence in rat liver cell sap of phosphoprotein phosphatase, which acts on phosphorylated pyruvate kinase. In vitro experiments strongly indicate that L-type liver pyruvate kinase is an enzyme whose activity is regulated by reversible protein phosphorylation in vivo .