Efficacy of metmyoglobin and hemin as a catalyst of lipid peroxidation determined by using a new testing system.

A new quantitative approach to investigate the capability of iron heme complexes (HEM), metmyoglobin and hemin, to catalyze lipid peroxidation was elaborated. The oxidation of methyl linoleate in micellar solutions was used as a testing model. The key point was the determination of the rate of free radical generation, RIN, calculated from the rate of oxygen consumption. The HEM catalytic activity was characterized by two independent parameters: by reactivity and by its resistance to degradation. Both parameters were found to be pH-dependent. The reactivity was expressed as the effective rate constant for the reaction of HEM with lipid hydroperoxide. The resistance to degradation was characterized by the rate of the decrease in RIN with time and also by the regeneration coefficient, which shows how many active free radicals can be generated by one molecule of HEM. Both Hemin and metMB were found to be very effective catalysts even at nanomolar concentrations. The effective regeneration of active forms of HEM was observed. The catalytic activity of HEM was rapidly reduced with time. The kinetic scheme of the process under consideration was suggested, and this was applied for kinetic computer simulations.