Identification of initiating agents in myoglobin-induced lipid peroxidation.

Reaction of metmyoglobin with peroxides is known to involve the formation, possibly via a porphyrin radical-cation, of a ferryl (iron(IV)-oxo) species and a protein radical; there is a little information available as to which of these species initiates the damage which is observed on incubating membrane fractions with such mixtures. It is shown in this study that the initial protein radical, which is a tyrosine phenoxyl radical centered at position 103 in the protein, does not react rapidly with erythrocyte membranes. However a tyrosine peroxyl radical, formed by addition of oxygen to this species, does react rapidly, and it is concluded that this radical, together with the ferryl species, is an important initiating species in myoglobin-induced lipid peroxidation.