MECHANISM OF REACTION OF MYOGLOBIN WITH THE LIPID HYDROPEROXIDE HYDROPEROXYOCTADECADIENOIC ACID

The reaction between myoglobin and the lipid hydroperoxide 13(S)-hydro peroxy-9,11(cis, trans)-octadecadienoic acid (HPODE) was studied kinet ically by spectrophotometric, polarographic and analytical methods, Me tmyoglobin catalysed the decomposition of HPODE, resulting in peroxide , oxygen and conjugated diene depletion, together with the transient p roduction of ferryl myoglobin. The reaction stoichiometry was 2:1:1 fo r peroxide to oxygen to conjugated diene, whereas the myoglobin remain ed generally intact. This stoichiometry and the rates of change of con jugated diene and ferryl myoglobin concentrations were not completely consistent with previously proposed mechanisms. We propose a novel mec hanism in which HPODE reacts with both ferric myoglobin and ferryl myo globin to form a redox cycle. Both peroxyl and alkoxyl radicals are pr oduced, explaining the observed stoichiometry of peroxide, oxygen and conjugated diene depletion and the transient appearance of ferryl myog lobin. Computer simulation shows that this mechanism is fully capable of reproducing the observed time courses of all components.