Studies on the Freeze Denaturation of Squid Actomyosin*i

Denaturation of squid actomyosin during frozen storage was studied by measuring solubility, viscosity, and ATPase activity, and by uitracentrifugal analysis and SDS-electrophoresis. The additive effect of sodium glutamate, well-known for its cryoprotective effect on the freeze denatura-tion of carp actomyosin, was also checked. When solutions (0.6 M KCI) or suspensions (0.05 M KCl) of the isolated squid actomyosin were stored at _20DC, the solubility, reduced viscosity and ATPase activity decreased with the length of frozen storage. The ultracentrifugal patterns showed that aggregation proceeded during frozen storage. Evidently, sodium glutamate prevented the freeze denaturation of squid actomyosin, as in the case of carp actomyosin. When the mantle muscle of squid was freeze-stored at- 20DC and extracted with 0.6 M KCI, the amount of soluble actomyosin extractable from the frozen meat and the ATPase activity of the actomyosin were de-creased only slightly even after a long freezing period. This differed from the results with isolated actomyosin. Reflecting the importance of the keeping quality of frozen fish, a great number of studies have been published so far on the freeze denaturation of fis