Biochemical properties of akazara scallop myosin hybridized with the foreign regulatory light chains.

Abstract

The roles of regulatory light chains in the biochemical function of molluscan myosin were studied by hybridizing “desensitized” akazara scallop myosin with the regulatory light chains of rabbit skeletal, chicken gizzard, rainbow trout dorsal, and crayfish abdominal myosins. By measuring the Mg-ATPase activities of myosin and actomyosin, and the superprecipitation activity of actomyosin, the following results were obtained:1) All the foreign regulatory light chains we tested, led to the inhibition of Mg-ATPase activities of both desensitized myosin and acto-desensitized myosin in the absence of Ca2+. Whereas, whether the inhibition of Mg-ATPase activities was neutralized by Ca2+ or not, i.e. Ca2+-sensitivity of the Mg-ATPase activities recovered or not, was dependent on the species of the regulatory light chain. In this respect, these regulatory light chains could be classified into two groups; One includes the regulatory light chains of akazara scallop, chicken gizzard, and crayfish abdominal myosins, which afford the Ca2+-sensitivity to desensitized myosin, and the other includes those of rabbit skeletal and rainbow trout dorsal myosins, which afford no Ca2+-sensitivity.2) The superprecipitation activity of skeletal acto-akazara scallop myosin was remarkably decreased by the removal of regulatory light chains. However, the decreased superprecipitation activity recovered on the binding of either akazara scallop regulatory light chains or foreign regulatory light chains. These results may indicate that foreign regulatory light chains as well as molluscan regulatory light chains can maintain the myosin conformation that is indispensable for actin-myosin interaction.