Characterization of an autophosphorylation-dependent multifunctional protein kinase from liver.

S. D. Yang, S. Y. Chang, T. R. Soderling

    Research output: Contribution to journalArticle

    15 Scopus citations

    Abstract

    A cyclic nucleotide- and Ca2+-independent protein kinase has been identified and purified from pig liver to apparent homogeneity. This independent protein kinase is basically inactive but can be activated by a 4-min incubation with 0.25 mM ATP and 2 mM Mg2+. This ATP X Mg-mediated activation appears to involve an intramolecular autophosphorylation as it is independent of kinase concentration. Phosphoamino acid analysis further indicates that this intramolecular autophosphorylation/activation process is predominantly on a serine residue. The nonphosphorylated, inactive form of the kinase is extremely trypsin-labile, whereas the phosphorylated, active kinase is more resistant to trypsin, suggesting a conformational change during the activation process. Autophosphorylation/activation of the kinase is enhanced 2-fold by heparin (0.4 unit/ml) and blocked by phosphatidylserine (0.4 mg/ml). Partial dephosphorylation of the phosphorylated kinase is associated with a time-dependent decrease in the enzyme activity. This autophosphorylation-dependent protein kinase phosphorylates glycogen synthase (Km = 8 microM) at sites 2 and 3, resulting in inactivation of glycogen synthase. The results indicate that this independent kinase may represent a previously undiscovered liver multifunctional protein kinase which can be regulated by reversible phosphorylation.

    Original languageEnglish (US)
    Pages (from-to)9421-9427
    Number of pages7
    JournalJournal of Biological Chemistry
    Volume262
    Issue number19
    StatePublished - Jul 5 1987

    ASJC Scopus subject areas

    • Biochemistry
    • Molecular Biology
    • Cell Biology

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