The ATP,Mg‐dependent protein phosphatase: Regulation by casein kinase‐1

Abstract

The free modulator subunit of the ATP,Mg‐dependent phosphatase is phosphorylated up to 1 mol per mol by casein kinase‐1, up to 1.85 mol per mol after dephosphorylation by the PCS_H1 phosphatase, but 10‐fold less when purified in the presence of NaF, suggesting an in vivo phosphorylation of the casein kinase‐1 sites. Peptide mapping of ³²P‐modulator labeled by casein kinase‐1 or ‐2 shows a different phosphorylation pattern. Phosphorylation of the inactive phosphatase by casein kinase‐1 prevents the subsequent kinase F_A‐mediated activation, while it does not impair the activated phosphatase.