Separation of rat-liver phosphoprotein phosphatases active on phosphorylated pyruvate kinase (type L).

The substrate specificity of rat liver phosphoprotein phosphatases has been investigated. The enzymes were resolved into three fractions, termed A, B and C, on elution from DEAE-cellulose with apparent molecular weights, as determined by Sephadex G-200 chromatography, of approximately 250 000, 250 000 and 140 000, respectively. All fractions catalyzed the dephosphorylation of calf-thymus phosphohistones, salmon phosphoprotamine and rabbit skeletal muscle phosphorylase a. The major portion of the activity towards these substrates was found in fraction B. The activity towards rat liver phosphopyruvate kinase (type L) resided almost exclusively in fractions B and C. It is concluded that rat liver contains multiple forms of phosphoprotein phosphatases and that phosphatases of fraction B and C are the major activities towards phosphopyruvate kinase.