TYPE-II REGULATORY SUBUNIT OF CAMP-DEPENDENT PROTEIN-KINASE - PHOSPHORYLATION BY CASEIN KINASE-II AT A SITE THAT IS ALSO PHOSPHORYLATED INVIVO

  • 1 January 1982
    • journal article
    • research article
    • Vol. 257  (17) , 440-445
Abstract
A study of the phosphorylated sites on the regulatory subunit of type II cAMP-dependent protein kinase [from bovine heart or rat skeletal muscle] is described. The site of autophosphorylation, previously reported, is found to contain the only residue phosphorylated by the catalytic subunit. Endogenous protein-bound phosphate, present at a 2nd site, is observed in the NH2-terminal region of purified type II regulatory subunit. A serine residue in this same domain of type II regulatory subunit is phosphorylated in vitro by casein kinase II. The stoichiometry of phosphate incorporation by casein kinase II indicates a single site of phosphorylation that is equivalent to the site containing the endogenous phosphate. The apparent Km and Vmax of casein kinase II for the phosphorylation of purified type II regulatory subunit containing 0.55 molar equivalents of endogenous phosphate are 36 .mu.M and 3.5 .mu.mol/min per mg, respectively. Phosphatase treatment of type II regulatory subunit decreased the determined Km to 13 .mu.M but does not change the Vmax consistent with the suggestion that casein kinase II is phosphorylating a site partially occupied by endogenous phosphate. Comparison of peptide maps of type II regulatory subunit phosphorylated in vitro by casein kinase II with in vivo modified type II regulatory subunit indicates that the site modified in vitro is also phosphorylated in vivo.

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