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  • Title: Calponin phosphatase from smooth muscle: a possible role of type 1 protein phosphatase in smooth muscle relaxation.
    Author: Ichikawa K, Ito M, Okubo S, Konishi T, Nakano T, Mino T, Nakamura F, Naka M, Tanaka T.
    Journal: Biochem Biophys Res Commun; 1993 Jun 30; 193(3):827-33. PubMed ID: 8391807.
    Abstract:
    Smooth muscle myosin bound phosphatase (MBP) purified from chicken gizzard, which is a holoenzyme of type 1 delta protein phosphatase and dephosphorylated intact myosin, catalyzed the dephosphorylation of calponin phosphorylated by protein kinase C (PK-C). The Km of MBP for calponin was 0.6 microM and the Vmax was 350 nmol/min/mg. All of the multiple sites of phosphorylation by PK-C of calponin were completely dephosphorylated by MBP. Functionally, calponin dephosphorylated by MBP recovered its inhibitory effect on the actin-activated Mg(2+)-ATPase activity of myosin. Therefore, these results suggest that a type 1 delta protein phosphatase causes relaxation of smooth muscle by the dephosphorylation not only of myosin but also of calponin.
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