The properties and function of invertebrate new muscle protein

We found out a new protein from natural actomyosin prepared from adductor m uscle of Hokki clam, bivalve shell. We isolated this protein and determined some properties. It has a large molecular weight (230 kDa) and the star di agram of amino acid composition was very similar to that of paramyosin (110 kDa). When this protein was added to Hokki clam myosin, the Mg2+-ATPase ac tivity was more activated in the presence of 10(-7) M Ca2+ and further inhi bited in the presence of 10(-4) M Ca2+ as compared with those of myosin. Fr om these results, we suggest that Hokki clam adductor muscle contains anoth er myosin-linked regulatory protein, myonin, which is different from the my osin-linked system, the myosin light chain-linked system. We named this pro tein 'myonin'. (Mol Cell Biochem 190: 63-66, 1999).