コイミオシンBの-8°C凍結貯蔵および-8°C過冷却貯蔵中の変性

抄録

In order to study the participation of concentrated salt solution in denaturation of myosin Bduring frozen storage, carp myosin B in KCI solution was stored for 17 days in frozen and super-cooled state at-8°C and the extent of denaturation was compared. The comparison was also made with that of myosin B stored at O°C and frozen-stored at-20°C. The extent of denatura-tion was followed up by changes in solubility, Ca-ATPase activity, reduced viscosity and streamingbirefringence of the solutign, and form of myosin B filaments. The apparent rate constant forinactivation of Ca-ATPase(k_D, day^-1)of myosin B in O storage was 0.018 and those in-8°C-supercooled-and-20°C-frozen-storage were equally 0.074. In contrast to the above values, the k_D in-8°C-frozen-storage was 0.691 at a very early stage(0-2 days)and 0.028 for the period ofthe subsequent 15 days. The reduced viscosity of the myosin B solution decreased rapidly withinaday when stored in the frozen state at-8°C, but decreased very slowly within the first 3 dayswhen stored in the supercooled state at the same temperature. In the case of the-8°C-frozen-storage, the streaming birefringence was not detected after a day, but in the cases of three otherstorage conditions it could be observed. The electron microscopic observation showed that thedeformation of myosin B filaments was accelerated is the early stage of-8°C-frozen-storage.Their filamentous form changed to granular form and the filamentous form of myosin B disap-peared after 2 days. During both-8°C-supercooled-storage and-20°C-frozen-Storage, themorphological change of myosin B filaments occurred gradually and the extent of the change was very similar in each case, and the filamentous form of myosin B remained intact even after 17 days. These findings show that the denaturation of myosin B during-8°C-frozen-storage isaccelerated to some extent by temperature depression itself and significantly by concentrated unfrozen KCI solution.