Isolation and characterization of myosin from walleye pollack surimi

Actomyosin was extracted from myofibrils obtained from walleye pollack frozen surimi with 0.5 M KCl, 1 M sorbitol, and 1 mM Mg-ATP. Myosin was separated from F-actin by ultracentrifugation in the presence of MgCl2 and ATP. The myosin consisted of heavy chains of Mr 200,000 and light chains of Mr 25,000, 18,000, and 17,000. Ca-ATPase activity of the myosin decreased approximately 20% per day at 0 degrees C in 0.5 M KCl (pH 7.0) containing 1 M sorbitol. Ca-ATPase specific activity was approximately 8 times lower but EDTA-ATPase specific activity was several times higher than those of rabbit myosin at 0.05-0.5 M KCl, although the respective activities of both myosins showed similar dependences on KCI and pH. The Mg-ATPase activity of pollack myosin was increased approximately 100 times by the addition of an equal weight of rabbit F-actin and the activity was approximately 5 times higher than that of rabbit myosin. On the other hand, the actomyosin showed a significant increase in Mg-ATPase activity upon incubating at 20-30 degrees C, probably due to some irreversible conformational changes of myosin. The pollack myosin formed mini-filaments of about 0.5 mu m length and the filaments tended to aggregate with each other.