Inhibitory Regulation by Calcium Ion of Myosin ATPase Activity : Binding of Calcium Ion and Phosphorylation of Myosin
In 1980, we prepared native actomyosin from the lower eukaryote, Physarum, by referring to published methods (see Kohama and Ebashi, 1986, for a review). Our preparation of actomyosin showed Casensitive ATPase activity with novel characteristics : the activity was highest in EGTA-containing solutions and was depressed by increasing concentrations of Ca2+ (Kohama et al., 1980). Thus far, regulation by Ca2+ has exclusively been shown to involve activation, and our result is the first example of an inhibitory mode of regulation by Ca2+ (Ebashi et al, 1982). We further purified myosin from the Physarum actomyosin by newly developed methods (Kohama and Kendrick-Jones, 1986; Kohama et al., 1986), and we found that this myosin is composed of a pair of heavy chains with molecular weight of 230 Kd each in SDS PAGE and two pairs of light chains having weights of 18 Kd and 14 Kd in SDS PAGE. Furthermore, the isolated myosin is phosphorylated, having about 4 mol Pi per mol of myosin (Kohama and Kendrick-Jones, 1986).
KeywordsATPase Activity Scallop Myosin Potato Acid Phosphatase Dephosphorylated Myosin
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