Requirement of Phosphorylation of Physarum Myosin Heavy Chain for Thick Filament Formation, Actin Activation of Mg2+-ATPase Activity, and Ca2+-Inhibitory Superprecipitation12

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Abstract
In an attempt to elucidate the Ca2+-regulated mechanism of motility in Physarum plasmodia, we improved the preparation method for myosin B and pure myosin. The obtained results are as follows: The above results clearly show that the phosphorylation of myosin HC is indispensable to ATP-induced superprecipitation, the actin-activated Mg2+-ATPase activity, and the formation of thick filaments of myosin. A myosin-linked factor(s) that inhibits an actin-myosin interaction in a Ca2+ manner may exist.