NATIVE MYOSIN FROM ADULT-RABBIT SKELETAL-MUSCLE - ISOENZYMES AND STATES OF AGGREGATION

The globular heads of skeletal muscle myosin have been shown to exist as isoenzymes S1 (A1) and S1 (A2), and there are also isoforms of the heavy chains, Using capillary electrophoresis, we found two dominant i soenzymes of the whole native myosin molecule, in agreement with what has previously been found by various techniques for native and nondena tured myosin from adult rabbits. Findings about possible states of agg regation of myosin and its heads are contradictory. By analytical ultr acentrifugation, we confirmed the existence of a tail-tail dimer, By l aser light scattering, we found a head-head dimer in the presence of M gATP. Capillary electrophoresis coupled with analytical ultracentrifug ation and laser light scattering led us to refine these results. We fo und tail-tail dimers in a conventional buffer. We found tail-tail and head-head dimers in the presence of 0.5 mM MgATP and pure head-head di mers in the presence of 6 mM MgATP. All the dimers were homodimers. Na ming the dominant isoenzymes of myosin a and b, we observed tail-tail dimers with isoenzyme a (TaTa) and with isoenzyme b (TbTb) and also he ad-head dimers with isoenzyme a (HaHa) and with isoenzyme b (HbHb).