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

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 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 chains of smooth myosin was almost the same as that of striated myosin of scallop except for a slight difference in Asp content.