Studies on Phosphoprotein Phosphatase in Chick Embryo

Part IV. Substrate Specificity and Effects of Inhibitors

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Several properties of partially purified phosphoprotein phosphatase from chick embryo are described. The enzyme was active toward casein, phosvitin and phosphopeptone, but not toward low molecular weight phosphate esters including aliphatic and aromatic phosphomonoesters, a phosphodiester, pyrophosphates and phosphoamides. The enzyme was not activated by reducing compounds. Heavy metal ions and sulfhydryl inhibitors inhibited the enzyme activity, but the inhibited enzyme was partially reactivated with cysteine. Metal chelating agents also inhibited the activity. To the oxalate treated enzyme, Fe⁺⁺and Co⁺⁺had a stimulatory effect. Differences in property between phosphoprotein phosphatases of chick embryo and of mammalian tissues are discussed.