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

Myoglobin (Mb) has a physiological function acting as the 02 buffer to counteract the fluctuating needs of 02 in muscle tissue.0 Mostly, this can be ascribed to its oxygen affinity. In contrast to a reversible oxygenation of the pro tein, the ferrous porphyrin is rapidly and irreversibly oxi dized by oxygen. Complex mechanisms of this oxidation have been previously proposed.2-5) Such knowledge clarifies the role of myoglobin in stabilizing the ferrous state. The globin itself has judiciously developed the heme pocket environments by the presence of nonpolar or basic amino acid residues to limit access of protons to the oxygen binding site, thus preventing an autoxidation.5,6) However, myoglobins from various species may have different heme pocket environments due to certain differ ent amino acid sequences .1,7-10) Some effects of chemical and physical properties on the autoxidation of fish my oglobins have been studied.11-16) The autoxidation reaction is mainly dependent on pH, temperature and salt concen tration. In particular, the proton-catalyzed process has been proposed as a diagnostic probe into differences in the heme reactivity and the heme environment of oxymy oglobin (MbO2) from different sources .7,17-19) In the present study, the autoxidation rate of holomyoglobin from some fish species was investigated as a function of temperature at neutral pH. Differences in heat-denaturation behaviors were found between holomyoglobin201 and reconstituted myoglobin.21) In con nection with those, their autoxidation rate of the recon stituted myoglobin was also investigated.