結晶Myosinの溶解性に関する研究 I. pH及びイオン強度の影響

Recently, Spicer et al. have reported their results concerning two zones of precipitation in myosin caused under a certain ionic strength and pH (3). The characters in respect to the solubility of actomyosin (AM) are the reflections of those of myosin, even if it is sharper in the ease of myosin than in AM. Therefore, the new phenomenon mentioned above in myosin is important to the AM-ATP (adenosinetriphosphate) interaction. Accordingly, the author studied the effect of various pH and ionic strength on the solubility of myosin in detail. The results are as follows: 1) Myosin is precipitated twice with increasing pH under a certain constant ionic strength (Fig. 1). In this case, alkaline precipitate is formed after relatively prolonged intervals (Fig. 3). 2) The pH value where myosin precipitation occurs decreases with increasing ionic strength. As a consequence, the above mentioned two zones of myosin precipitation converge (Fig. 1). On the other hand, these zones approach likewise with decreasing ionic strength below 0.10. 3) The grade of solubility of the two precipitationi is different, namely, alkaline is more soluble than acid (Fig. 2). 4) At pH 5.6 and ionic strength 0.38, the turbidity that develops at 25℃ is largely reversed at 0℃. Accordingly, the formation of precipitation is endothermic (Fig. 3). 5) At pH 6.6 and ionic strength 0.16, the turbidity develops abruptly at 0℃, however, at pH 8.0 and ionic strength 0.16, the turbidity does not develop till after two hours, in spite of changing the tempera-ture (0℃→25℃, 25℃→0℃), but develops abruptly at 25℃ after two hours following beginning of reaction (Fig. 3)