Native Myosin from Adult Rabbit Skeletal Muscle:  Isoenzymes and States of Aggregation

Abstract

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 isoenzymes of the whole native myosin molecule, in agreement with what has previously been found by various techniques for native and nondenatured myosin from adult rabbits. Findings about possible states of aggregation of myosin and its heads are contradictory. By analytical ultracentrifugation, we confirmed the existence of a tail-tail dimer. By laser light scattering, we found a head-head dimer in the presence of MgATP. Capillary electrophoresis coupled with analytical ultracentrifugation and laser light scattering led us to refine these results. We found 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 dimers in the presence of 6 mM MgATP. All the dimers were homodimers. Naming the dominant isoenzymes of myosin a and b, we observed tail-tail dimers with isoenzyme a (TaTa) and with isoenzyme b (TbTb) and also head-head dimers with isoenzyme a (HaHa) and with isoenzyme b (HbHb).

Dimerization of Native Myosin LC2(RLC)-Free Subfragment 1 from Adult Rabbit Skeletal Muscle

“…We confirm its existence and report some new factors influencing the monomer-dimer equilibrium (e.g., temperature). This work is complementary to studies presented in the 1980s by our group and more recently by Grussaute et al (11) and Morel et al (5). In ‡ Laboratoire de Biologie.…”

“…Probably, the difference of behavior results from the different cleavages of RLC-free S1 and Mg.S1. Nonetheless, Bachouchi et al (3) found that the major properties of Mg.S1 are qualitatively (not quantitatively) similar to those of LC2free S1, in agreement with the fact that the myosin heads on whole myosin molecules can dimerize in the presence of MgATP (5). In light of the recent positive evidence for S1 dimers (11), Mg.S1 dimers (12), and myosin head-head dimers (5), we undertook further experimental studies on the S1 dimer.…”

“…The existence of the dimeric state of S1 was not accepted for 12-13 years. However, Stewart et al (4) described headto-head interactions of heads belonging to different myosin molecules (Limulus and scorpion thick filaments), in agreement with Morel et al (5), who found that native myosin can form head-head dimers. The work of Levine et al (6) showing that it is possible to use bis 22 ATP to crosslink axially sequential myosin molecules along each helical strand was not intended to demonstrate that myosin exists as dimers or in any other particular interactive form.…”

“…The question arises as to whether an intrinsic viscosity of 19.8 cm 3 /g corresponds to a pure RLC-free S1 dimer. We used the laser light scattering technique described under Materials and Methods and in Morel et al (5) to study D t 20,w for both the S1 monomer (buffer A) and the S1 dimer (buffer B + 6 mM ATP). The results giving D t 20,w (c) are shown in Figure 5.…”

“…Laser Light Scattering. The methods used have been extensively described by Morel et al (5). The index of polydispersity was around 0.1, and although very low, it is due to the 1% of heavy material in native S1 (11).…”