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    Arch Biochem Biophys. 1991 Aug 1;288(2):538-42.

    Determination of the phosphorylation sites of smooth muscle caldesmon by protein kinase C.

    Source

    Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio 44106.

    Abstract

    Smooth muscle caldesmon was phosphorylated by protein kinase C up to 1.90 mol P/mol caldesmon. Phosphorylated caldesmon was completely digested by trypsin and the produced phosphopeptides were purified by C-8 and C-18 reverse phase chromatography. Four phosphopeptides were determined and two phosphoserines were identified. Both were localized in the C-terminal domain at serine-587 and serine-726. By following the time course of phosphorylation, serine-587 was found to be the preferred site. Effects of the phosphorylation of caldesmon by protein C on the inhibition of acto-H-meromyosin ATPase activity was also examined. While unphosphorylated caldesmon inhibited the ATPase activity by 60%, phosphorylated caldesmon hardly inhibited the ATPase activity. Therefore, it was concluded that the phosphorylation at serine-726 and serine-587 reverses the inhibitory activity of caldesmon.

    PMID:
    1898046
    [PubMed - indexed for MEDLINE]

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