血合筋肉の化学的研究-VI : 血合ミオグロビン及び血液ヘモグロビンの溶解度

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The solubilities of myoglobins (Mbs) of tuna, Parathunnus sibi and swordfish, Makaira mitsukurii were determined in the phosphate buffer solution of high ionic strength and compared with those of some other Mbs and hemoglobins (Hbs). In the first experiment, solubility determinations were carried out on carbonyl derivatives of these pigments in the phosphate buffer solution of constant pH (6.6) and at constant temperature (20°C.). The results obtained are shown in Fig. 1 and Table 1. It is obvious that the solubilities of Mbs of tuna and swordfish lie between fish or mammalian Hbs on one side and horse Mb (and probably those of beef, dog, etc., as judged from the solubility data on these species and horse Mbs in concentrated ammonium sulfate solution9)) on the other side, rather being nearer to the former. It seems, therefore, that DRABKINs method of Mb determination2), based on the selective salting-out of Hb in phosphate buffer solution (3 M, pH 6.6, and ?? /2 ca. 6), is not always adaptable in cases of fish. In addition, the solubilities of carbonyl-, reduced-, cyanmet-, and met-Mb of tuna were compared and found to be very close to each other, although met-form is slightly more soluble than the others. Recryst- allization of this pigment effected no appreciable change in the solubility. The second experiment, performed to study the influence of pH and temperature on the solubility of tuna met-Mb, resulted in some interesting findings (Figs. 2 A and 2 B). As shown in Fig. 2 A, this Mb has no minimal solubility between pH 7.20 and 6.00 and that was true also between pH 6.20 and 4.54, in spite of the fact that the isoelectric point of this Mb is found between pH 6 and 713)14). This phenomenon is perhaps due to the interaction between the Mb molecule and some of the ionic components of the salt. Fig. 2B shows that this protein has a typical negative temperature coefficient over a wider range of temperature (0°-44°C.), which seems to be one of the relatively rare cases. Thus fish Mbs proved to be fairly species-specific in respect to solubility, as well as to the other properties previously reported1).

血合筋肉の化学的研究-VI : 血合ミオグロビン及び血液ヘモグロビンの溶解度

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