Purification and properties of a phosphoprotein phosphatase from rat liver

Abstract

A phosphoprotein phosphatase (phosphoprotein phosphohydrolase, EC 3.1.3.16) has been partially purified from rat liver homogenates by (NH4)2SO4 and ethanol precipitations followed by DEAE-cellulose and Sepharose 6B chromatography. The phosphoprotein phosphatase is capable of cleaving [32P]phosphate from radiolabelled phosphopyruvate kinase (type L) (EC 2.7.1.40), phosphohistones, and phosphoprotamine. However, it did not detectably dephosphorylate ATP, ADP, DL-phosphorylserine or beta-glycerophosphate. Dephosphorylation of [32P]phosphopyruvate kinase was stimulated by divalent cations and inhibited by ATP, ADP, Fru-1,6-P2, and orthophosphate. Divalene cations could reverse inhibition induced by ADP or ATP. At least one function of the phosphoprotein phosphatase may be to remove phosphate groups from the phosphorylated form of pyruvate kinase in the liver.