EFFECT OF HEATING ON AUTOXIDATION RATE OF FISH HOLO-MYOGLOBIN AND RECONSTITUTED-MYOGLOBIN

The autoxidation rate of oxymyoglobin (MbO(2)) from sardine, saury, ca rp and sheep holoMb was measured as a function of temperature after he ating and cooling. The observed first-order rate constant (k(obs)) is found to be temperature dependent. The k(obs) values for MbO(2) are no t so different among these fish species at the same given temperature, but found to be higher, by 2.5 similar to 4.2 times as a whole, than those of sheep Mb. In connection with a structural perturbation, the a utoxidation rate of a reconstituted MbO(2) was measured directly while heating. In the same way, the assigned k(obs)' value at normal condit ions for bonito reconstituted MbO(2) is also found to be higher than t hat of the sperm whale one, but their k(obs)' values are not different under heat denaturation. The autoxidation reaction has been thermally mediated through structural unfolding/refolding. These results sugges t that according to an origin of the structure looseness associated wi th the heme pocket perturbation, thus fish myoglobins show cooperative ly higher susceptibility to the autoxidation of MbO(2) than mammalian myoglobins.