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  • Title: Calmodulin activates inositol 1,4,5-trisphosphate 3-kinase activity in pig aortic smooth muscle.
    Author: Yamaguchi K, Hirata M, Kuriyama H.
    Journal: Biochem J; 1987 Jun 15; 244(3):787-91. PubMed ID: 2833220.
    Abstract:
    The effects of calmodulin (CaM) on inositol 1,4,5-trisphosphate (InsP3) 3-kinase activity in pig aortic smooth muscle were examined. The cytosol fraction of muscle cells, containing 1.2-2.0 micrograms of CaM/mg of cytosol protein (thus 0.12-0.2%, w/w), showed a Ca2+-dependent InsP3 3-kinase activity, and there was no further activation by exogenous addition of CaM purified from dog brain. (NH4)2SO4 fractionation of the cytosol fraction revealed that a 20-60%-satd.-(NH4)2SO4 fraction was rich in the enzyme activity, and the activity without exogenous CaM was still dependent on Ca2+, although the CaM content in this fraction was minute (0.013-0.016%, w/w). The kinase activity observed in the absence of exogenous CaM became insensitive to Ca2+ when a 20-60%-satd.-(NH4)2SO4 fraction was applied to a DEAE-cellulose column, but exogenous addition of CaM increased the enzyme activity from 80-120 to 450 pmol/min per mg of protein, with addition of 10 microM free Ca2+. A fraction separated by DEAE-cellulose chromatography was applied to a CaM affinity column. The kinase activity was retained on the column in the presence of Ca2+, and was eluted by lowering the free Ca2+ concentration by adding EGTA. These results directly show that CaM activates InsP3 3-kinase activity and the enzyme becomes sensitive to Ca2+.
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