Abstract
Heat coagulability of myoglobin (Mb) and hemoglobin (Hb) of some fishes was compared under the conditions described below. Mb or Hb aq. solution was mixed with phosphate buffer to obtain a final concentration of pigment of 0.075%, and a final concentration and a final pH value of buffer, 0.2M and 6.7, respectively. These conditions were based on the results of preliminary experiments (cf. Figs. 1 and 2). The solution of various derivatives of pigment was prepared by ordinary methods, using 1 drop of 1% ferricyanide solution as oxidizing agent, 3mg. of solid KCN for cyanmet formation, and 3mg. of solid Na2S2O4 as reducer, per 5ml. of the solution.
The subsequent procedure is essentially the same as that of BETKE7). Each 5ml. of the solution was pipetted into test tubes (16×ll0mm.), the tubes being stoppered with rubber stoppers and kept immersed in an ice-water bath. After heating at various temperatures in a water bath for 5min., each tube was immersed immediately in the ice-water bath again, and the concentration of pigment in the supernatant determined spectrophotometrically. Then a curve (termed heat coagulation curve) is obtained by plotting the remaining amounts of pig-ment against the temperatures. The heat coagulation curves of both pigments are shown in Fig. 3. The noticeable points of these results are as follows:
(1) The positions of heat coagulation curves were different among species, Mb and Hb, and derivatives, and the slope of curve of Mb was generally steeper than that of Hb.
(2) On both Mb and Hb, met form was the most heat sensitive, followed by cyanmet form, while carbonyl and reduced forms were comparatively stable.
(3) Each derivative of Hb in a species coagulated at far lower temperatures than the cor-responding one of Mb, and this tendency was marked in met and cyanmet forms.
(4) Species specificity of Mb in heat coagulability was fairly evident, which makes it possi-ble to divide the fishes tested into two groups; a group having heat resistant Mb such as tuna, bonito, and swordfish, and another group having heat irresistible Mb such as yellowtail, saury-pike, and mackerel. Both Mb and Hb of horse, studied for reference, were found to be very heat resistant as compared with the pigments of fish.
(5) Under the conditions employed, however, there was a limit of temperature beyond which no further coagulation of pigment was measured, in the case of Mb of bonito, swordfish, and horse.
