Abstract
The biochemical and physicochemical properties of myofibrillar proteins from Japanese stingfish dorsal muscle were investigated. On SDS-PAGE, the molecular weights of each protein were as follows: myosin, 200 kDa; actin, 42 kDa; heavy meromyosin, 125 kDa, and light meromyosin, 66 and 77 kDa, respectively. Ca-ATPase activity of heavy meromyosin was higher than that of myosin, while EDTA-ATPase and Mg-ATPase activities were similar to those of myosin. The KCl-dependence of enzymatic activity was similar for both myosin and heavy meromyosin. Heavy meromyosin was more stable than myosin during storage at 4°C. The transition temperatures of each protein as determined by differential scanning calorimetry were as follows: myosin, 40.9°C, actin, 61.1°C, heavy meromyosin, 40.9 and 59.3°C, and light meromyosin, 62.2°C, respectively. When myosin was digested with trypsin, the portion corresponding to subfragment-1, the head portion of myosin, had a similar transition temperature to myosin. The portion corresponding to subfragment-2, the central region of myosin, corresponded to the high temperature-peak. The head portion has ATPase activity. On the other hand, LMM and the central region does not show this activity. These results indicated that the sensitivity of myosin constituents increased by trypsin digestion and suggested that the portion having ATPase activity had a high heat-sensitivity.
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