Identification of the sites on rabbit skeletal muscle protein phosphatase inhibitor-2 phosphorylated by casein kinase-II

Charles F B Holmes, Jeff Kuret, Alexander A K Chisholm, Philip Cohen

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    Inhibitor-2 was phosphorylated by casein kinase-II in vitro at a rate similar to that of glycogen synthase, a physiological substrate of this protein kinase. The major phosphorylation sites were identified as serines-86, -120 and -121, the peptide containing serines-120 and -121 being labelled about 2.5-fold more rapidly than that containing serine-86. The 13 residues C-terminal to serine-121 (SGEEDSDLSPEERE) contain seven acidic amino acids, while the six residues following serine-86 (SDTETTE) contain three. These results are consistent with the known specificity requirements of casein kinase-II. The three serines are C-terminal to the threonine (residue 72) whose phosphorylation by glycogen synthase kinase-3 is potentiated by prior phosphorylation with casein kinase-II. This reinforces the view that a C-terminal phosphoserine residue is important for the specificity of glycogen synthase kinase-3. Identification of the residues phosphorylated by casein kinase-II will facilitate further studies on the in vivo phosphorylation state of inhibitor-2.

    Original languageEnglish
    Pages (from-to)408-416
    Number of pages9
    JournalBiochimica et Biophysica Acta (BBA)/Protein Structure and Molecular
    Issue number3
    Publication statusPublished - 22 Apr 1986



    • casein kinase-11
    • Inhibitor-2
    • phosphorylated residue
    • protein phosphatase

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