Smooth Muscle of Scallop Adductor Contains at Least Two Kinds of Myosin1

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Abstract
Smooth muscle myosin purified from the small adductor of scallop, Patinopecten yessoensis, showed four distinct bands in the region of low molecular weight upon urea-gel electrophoresis. The two components showing the lowest mobilities in the electrophoresis were assigned as regulatory light chains and named as RLC-a and RLC-b. The component showing the highest mobility was SH-light chain, and the other component was not identified. Regulatory light chains of myosin prepared from the opaque portion of smooth muscle were estimated to be 40% RLC-a and 60% RLC-b, while those of myosin from the translucent portion were 20% RLC-a and 80% RLC-b. The rates of both myosin and actomyosin ATPases and of superprecipitation of actomyosin appear to be lower with myosin having RLC-a than with myosin having RLC-b. Myosin having RLC-a might be involved in catch contraction, which is seen mainly in the opaque portion of smooth muscle. Amino acid analysis revealed a marked difference in Arg contents between the two regulatory light chains. The amino acid composition of SH-light chain of smooth myosin was almost the same as that of striated myosin of scallop except for a slight difference in Asp content.