Biochemical and physicochemical properties of natural actomyosin (NAM) from pre-and post-spawned hake stored on ice were studied. At the beginning of storage both reduced viscosity and ATPases activities of NAM from post-spawned hake were about 3 times higher than those of the pre-spawned ones, except for the Mg2+-(Ca2+)-ATPase. Higher loss of functional components during pre-spawned hake NAM purification was found compared to NAM from postspawned fish. Reduced viscosity and Mg2+-(EGTA)-ATPase activity of NAM from both pre-and post-spawned hake decreased following ice storage. SDS-PAGE patterns of NAM from pre-spawned hake showed an absence of the myosin heavy chain and the presence of a 160 kDa component at zero time of storage. No proteolysis occurred in ice-stored fish caught in both gonadal stages.

Enzymatic activities assayed at beginning of storage in myofibrils from post-spawned hake were 3 X those in myofibrils from pre-spawned hake. Ca2+ sensitivity of myofibrils from pre-spawned hake was 40% less than that of myofibrils from post-spawned hake. The profiles of SDS-PAGE gels of pre-spawned myofibrils at beginning of storage showed a partially denatured myosin heavy chain, and polypeptide bands under myosin heavy chain. They probably represent proteolytic fragments produced by degradation of MHC in vivo. No proteolysis was detected in myofibrils during storage. These results help predict functional properties of fish proteins and changes during storage.

Denaturation of hake (Merluccius hubbsi) proteins was studied with DSC by monitoring T,,, of transitions and denaturation enthalpies. Whole muscle free of connective tissue showed two transitions (T,,,, 465°C and 75.3"C), and AH of 4.27 Cal/g. The exudative sarcoplasmic fraction showed three transitions (T,, 45.2"C, 59.O"C and 75.5"C) and AH of 3.92 Cal/g. The sarcoplasmic proteins from whole hake muscle contributed to both denaturation peaks. Muscle depleted of sarcoplasmic proteins by chloride extraction showed a higher thermal sensitivity and a diminished denaturation enthalpy on the second transition. This suggested an additional effect of chloride upon actin in addition to sarcoplasmic protein extraction. pH had an effect upon the native conformation of thick filament proteins, specifically myosin.