FIG. 5.

Reaction pathways for O₂(II)Mb, deoxy (II)Mb, met (III)Mb, ferryl Mb species, and protoporphyrin IX. Various pathways lead to hypervalent states of Mb with the concomitant generation of hydrophilic and hydrophobic oxidants. Oxidant challenge results in formation of met(III)Mb, cross-linked Mb, dissociation of ferriprotoporphyrin IX, and degradation of the protoporphyrin ring, which releases iron atoms. Phagocytes can facilitate bursts of H₂O₂ that degrade the protoporphyrin. LH represents a polyunsaturated fatty acid. LOOH represents a lipid hydroperoxide. Cross linking of Mb, dissociation of ferriprotoporphyrin IX, and ferryl Mb-mediated lipid oxidation occur more readily at reduced pH values. Image is adapted from ref. (62).