Proteolytic fragments from the lobster myosin molecule.

The fragments produced by proteolysis of lobster abdominal muscle myosin with trypsin, alpha-chymotrypsin and papain have been investigated by sodium dodecyl sulfate (SDS) gel electrophoresis. Essentially monodisperse populations of long rods are produced by alpha-chymotryptic and papain digestion of rabbit myosin but corresponding digestion of lobster myosin yields multicomponent species. Similarly the low ionic strength insoluble fraction from tryptic digestion of lobster myosin is polydisperse in contrast to essentially monodisperse light meromyosin from rabbit myosin. Comparative tryptic digestion of rabbit and lobster myosin papain long rods shows that the latter have five susceptible cleavage sites in the subfragment-2 region while rabbit long rods have only one: both long rods appear to have three cleavage sites in the light meromyosin region. The fragments produced by tryptic digestion of rabbit myosin papain long rods have been tentatively identified by comparison with fragments isolated from papain digests of rabbit heavy meromyosin and tryptic digests of rabbit light meromyosin. The results suggest differences in sensitivity to enzymic proteolysis between the subfragment-2 regions in rabbit and lobster myosin as well as relative differences in proteolytic sensitivity between the subfragment-2 and light meromyosin region within the individual molecules. Partial explanation of the observation is proposed on the basis of differences in heavy chain compositions.