Myosin kinase of molluscan smooth muscle: regulation by binding of calcium to the substrate and inhibition of myorod and twitchin phosphorylation by myosin

Ammonium sulfate fractionation and divalent cation precipitation were applied to purify major contractile proteins from relaxed actomyosin extracted from molluscan catch muscle myofibrils, as a supramolecular complex composed of twitchin (TW), myosin (MY), and myorod (MR). The phosphorylation of twitchin by PKA-like kinase and the phosphorylation of myosin and myorod by myosin-associated kinase were found to play crucial role in the development of the catch state.