Biochemical Studies on Changes in Fish Muscle Proteins Following Temperature Acclimation

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Since fish myofibrillar proteins account for over 50% in total muscle proteins, the feasibility of various kinds of fish meat for food processing and their stability during storage are regarded to be greatly influenced by the properties of myofibrillar proteins. This study was performed to answer the questions on which components and parts are most critical in changes of myofibrillar proteins of carp and goldfish during temperature acclimation, thus providing fisheries industry with valuable and foundamental information on fish muscles as food materials.1. Several individuals of carp were acclimated to either 10 or 30ﾟC for a minimum of 1 month and subjected to the preparation of myofibrils. Myofibrillar Mg^<2+>-ATPase activity of 10ﾟC-acclimated carp was significantly higher than that of 30ﾟC-acclimated fish when assayed at the same reaction temperatures. In contrast, the thermal stability at 40ﾟC of myofibrillar Ca^<2+->-ATPase of 10ﾟC-acclimated carp was several times lower than tha … More t of 30ﾟC-acclimated one. The similar results were obtained when acclimated goldfish were subjected to the same experiments.2. Myosin and its subfragment-1 (Sl) from 10ﾟC-acclimated carp showed a higher maximal initial velocity (Vmax) in actin-activated Mg^<2+>-ATPase activity than the 30ﾟC-acclimated counterparts, respectively, in a good agreement with the differences observed in myfibrillar Mg^<2+>-ATPase activity between the two acclimated groups. The 30ﾟC-acclimated myosin and Sl were again more thermostable than the 10ﾟC-acclimated counterparts, respectively.3. When a filamentous part of the myosin molecule, rod, was subjected to a limited proteolysis using alpha-chymotrypsin, the 10ﾟC-acclimated carp exhibited one L-meromyosin band in SDS-PAGE analysis. On the other hand, the 30ﾟC-acclimated carp gave three L-meromyosin bands. one of which was identical to the 10ﾟC-acclimated L-meromyosin.4. Peptide maps of myosin and Sl heavy chains and rod performed in SDS-gels were clearly different between 10ﾟC-and 30ﾟC-acclimated carp, suggesting that the primary structure of carp myosin molecule is altered during temperature acclimation. Less