Structural differences in the subfragment 1 and rod portions of myosin isozymes from adult and developing rat skeletal muscles.

During development of fast contracting skeletal muscle in the rat hindleg, embryonic and neonatal forms of the myosin heavy chain are present prior to the accumulation of the adult fast type ( Whalen , R. G., Sell, S. M., Butler-Browne, G.S., Schwartz, K., Bouveret, P., and Pinset -H arstr öm, I. (1981) Nature (Lond.) 292, 805-809). Polypeptide mapping of the heavy chain subunit using partial proteolysis in the presence of sodium dodecyl sulfate has shown differences in the cleavage patterns for these various heavy chains. Using this technique, we have now examined subfragments, which represent functional domains, from several different myosin isozymes. The heavy chains of the S-1 subfragments containing either light chain 1 or light chain 3 are indistinguishable for the neonatal or fast myosin isozymes. We also isolated the S-1 fragments and the alpha-helical COOH-terminal half of the molecule (rod) from rat embryonic, neonatal, and adult fast and slow myosin, as well as myosin from cardiac ventricles. All of these S-1 and rod fragments were different, indicating that the previously reported differences among these different myosin heavy chain isozymes are located in both the S-1 and rod subfragments for all myosins examined. However, the polypeptide maps of neonatal and adult fast S-1 show clear similarities, as do the maps of slow and cardiac S-1. These similarities in the two pairs of polypeptide maps were confirmed by the results of immunoblotting experiments using antibodies to adult fast and to slow myosin.