Abstract
In order to investigate whether the regulatory light chain (R-LC) removability depends on the R-LC or on desensitized myosin (DM) in the molluscan myosins, various hybridized myosins were prepared by combining of akazara DM with the R-LC of surf-clam foot and Atrina adductor myosins, and also of surf-clam DM with the R-LC of akazara scallop, ezo-giant scallop and Atrina adductor myosins. By using these myosins, it was observed that Ca-sensitivity of the Mg-ATPase activity of akazara intact myosin significantly decreased above 20°C, however, that of the akazara hybridized myosins with surf-clam and Atrina R-LCs practically unchanged. Whereas, the Ca-sensitivity of surf-clam myosin did not decrease above 25°C, but the surf-clam hybridized myosins with the akazara scallop and ezo-giant scallop R-LCs remarkably decreased.
It was also observed that the Ca2+ and Mg2+ concentrations for 50% dissociation of the R-LCs by heat (30°C)-treatment was estimated to be 4μM and 240μM for the akazara intact myosin, 0.2μM and 10μM for the akazara hybridized myosin with surf-clam R-LC, 0.2μM and 16μM for surf-clam intact myosin, and 3.7μM and 100μM for surf-clam hybridized myosin with akazara R-LC.
From these results, it is concluded that the difference in the affinity of R-LC to DM is de-pendent mainly on the R-LC rather than on the heavy chain.
