魚肉アクトミオシンの粘度に関する研究-II : 試料の保存による粘度変化

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Intrinsic viscosity of a fibrous molecule is equal to reduced viscosity, ηsp/c, as both concentration, c and velocity gradient, ??, approach zero; thus [η]=(ηsp/c)c→0 ?? →0 ?? →0 A tilting viscometer, as reported in the previous paper1), affords a convenient method for measuring viscosities at varying velocity gradients, but the method requires some 90 minutes for working out a whole measurement. Thus in the present experiment, stability of carp actomyosin solutions are examined, intending to know whether a stock solution could be used in the viscosity measurement as in the case of rabbit actomyosin. Stock solutions (0.3-0.5% solution of carp actomyosin in 0.6M KCl) were stored at 2-4°C and 20°C respectively, for 0, 1, 3, 4, 24hrs., and the solutions were diluted to a definite concentration (0.118%), relative viscosity being measured under varying velocity gradients. When stored at 2-4°C, the viscosity was found to have decreased after 1hr. and went on to decrease up to 3 hrs., approaching a limiting value (Table 1). When stored at 20°C, relative viscosity of carp actomyosin solution remained unchanged at least within 4 hrs., but after 24 hrs. a considerable decrease in viscosity was observed (Table 1). The same results were obtained in the similar experiments with the solutions diluted prior to storage to desired concentrations. Rabbit acotmyosin solution stored at 2°C for 24 hrs. showed no change in viscosity (Fig. 4). Actomyosin prepared from carp muscle stored at 0°C for 24 hrs. gave the same viscosity as that extracted from the muscle immediately after death (Fig. 8). Carp actomyosin prepared by 24hr. extraction gave a lower viscosity than that by 3min. extraction (Fig. 5). Carp actomyosin solution showed a decrease in intrinsic viscosity from 4 to 2 after 24hr. storage (Fig. 1) which corresponds to reduction in the axial ratio from 70 to 50 in the case of a prolate. This considerable decrease in asymmetry of the solute molecule may possibly cause decrease in both structural viscosity and inter-molecular interaction. Actually there was observed decrease in slopes of the curves XZ and XY in Fig. 1, which represent the relations of (ηsp/c)c→0- ?? and (ηsp/c) ?? →0-c respectively. The decrease in viscosity of the solution on storage, however, could not be attributable to dissociation of actomyosin into actin and myosin, since in salting-out curves the peak corresponding to actin failed to be observed with the both samples, the freshly prepared and stored solutions (Fig. 7). The value of ηsp/c usually decreases with concentration, c, but abnormal cases were occasionally experienced with stored actomyosin solution. Thus ηsp/c took a minimum value at a certain concentration (Figs. 2 and 3). A series of experiments carried out monthly revealed that this abnormal behavior in viscosity was found always with carps in July and August, and sometimes with carps in June (Table 2). An obvious difference in viscosity behavior was observed also among freshly prepared actomyosin solutions from rabbit and from carps of the two types (Fig. 10). Thus in rabbit, ln ηr/c is independent on concentration c, in normal carps increase in ln ηr/c is proportional to c, and in summer carps, the increase is greater than proportional to concentration.
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魚肉アクトミオシンの粘度に関する研究-II : 試料の保存による粘度変化

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