Abstract
Myosin and paramyosin were purified to homogeneity from deep abdominal flexor and extensor, and claw closer and opener muscles of crayfish. Myosins from fast muscle (deep abdominal flexor and extensor) consisted of one species of heavy chain and two species of light chains, Lf21 and Lf18. Myosin from slow muscle (opener) consisted of two species of heavy chains and three species of light chains, Ls31, Ls21 and Ls18. Closer myosin containing both fast and slow types of muscles contained Lf21, Lf18, Ls31, Ls21 and Ls18. The actin-Mg 2+-activated, Ca 2+-activated, and K +-EDTA-activated ATPase activities of the fast muscle type of myosins were much higher than those of the slow muscle type of myosin. The ATPase activities of closer myosin were in-between. The optimal KCI concentration of the K +-EDTA-activated ATPase activity of crayfish myosins was around 0.4 M as compared to 1 M in rabbit skeletal muscle. Opener myosin was contaminated with a 130 kDa protein. The latter turned out to be a paramyosin isoform. Slow type of muscle including closer muscle contained both 130 kDa and 105 kDa paramyosin isoforms. On the other hand, fast muscle expressed 110 kDa paramyosin isoform.
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