魚類ミオグロビンの自働酸化速度について

概要

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The autoxidation velocity of myoglobin (Mb) were investigated on crystalline specimens from fishes (two species of tuna, and skipjack), sei whale and horse. The results obtained were as follows. The autoxidation reaction of Mb, either from fish or from mammal, was of the first order with respect to unoxidized Mb (e. g., Figs. 2 and 4-6). The modes of effects of salt concentration, pH, and temperature on the autoxidation velocity were roughly common to all the species: The velocity constant (κ) was doubled by the increase of phosphate concentration from 0.2 M to 0.6 M (Fig. 3), and so was the case with the decrease of 0.3-0.4 pH unit (Fig. 7). The temperature coefficient was 4-5 (Table 1, Fig. 7). The velocity constant in the autoxidation was not so different among two species of tuna and skipjack, or between whale and horse. And the κ value for Mb of fish as a whole was 2.5-4 times larger than that of mammalian Mb. Mbs of tuna and horse showed maximum κ values at an oxygen pressure of 3.3-4.0mm.Hg (tuna) and 1.7mm.Hg (horse), which were close to the pressures for them at half saturation with oxygen, respectively (Fig. 10). The ratio of the maximum κ value to that at the atmospheric pressure was about 1.7 in the case of tuna Mb, which was far small, compared with about 3.6 in the case of horse Mb. That is, the effect of oxygen pressure on the autoxidation of Mb was slighter for tuna than for horse.