Effect of Heating on Autoxidation Rate of Fish Holo-and Reconstituted Myoglobins

Abstract

The autoxidation rate of oxymyoglobin (MbO₂) from sardine, saury, carp and sheep holoMb was measured as a function of temperature after heating and cooling. The observed first-order rate constant (k_obs) is found to be temperature dependent. The k_obs values for MbO₂ are not so different among these fish species at the same given temperature, but found to be higher, by 2.5_??_4.2 times as a whole, than those of sheep Mb. In connection with a structural perturbation, the autoxidation rate of a reconstituted MbO₂ was measured directly while heating. In the same way, the assigned k'_obs value at normal conditions for bonito reconstituted MbO₂ is also found to be higher than that of the sperm whale one, but their kobs values are not different under heat denaturation. The autoxidation reaction has been thermally mediated through structural unfolding/refolding. These results suggest that according to an origin of the structure looseness associated with the heme pocket perturbation, thus fish myoglobins show cooperatively higher susceptibility to the autoxidation of MbO₂ than mammalian myoglobins.