Physico-Chemical Properties of Squid Myosin

Abstract

Myosin of the obliquely striated mantle muscle of squid, Ommastrephes sloani pacificus, was isolated by the authors' method and its physico-chemical properties were studied. On ultracentrifugation, the myosin was found to be monodisperse but its sedimentation coefficient, S ??, _w, was 8.0 S, a higher value than those of the myosins of rabbit, fish, and some invertebrates. The intrinsic viscosity was 2.18 dl/g, which was comparable with those of other myosins. The amino acid composition did not show many differences except for Val and Arg, while the ratio of free SH-group content to total Cys/2 was to some extent lower in squid myosin than in myosins from other sources. The squid myosin appeared to have more S-S bridges in a molecule than do the myosins of fish and frog. The precipitate of squid myosin at ionic strength 0.05 showed, under an electron microscope, dumbbell shaped filaments with a shape and size similar to those of the myosins from other sources. Like the smooth muscle myosin, the squid myosin showed a tendency to aggregate with each other in a head to head arrangement. Though its sedimentation coefficient, S ??, _w, was higher, the overall data indicates that the squid myosin molecule has size and shape comparable with the myosins from other sources.