Lipid peroxidation by peroxidase-catalyzed bioactivation of tyrosine

Tyrosyl free radicals generated by the peroxidase-catalyzed oxidation of peptide tyrosyl residues are known to yield the stable cross-linked product dityrosine. In the present report, horseradish peroxidase is used as a model of peroxidase to study oxidative modifications of non-protein cellular components. Tyrosyl free radicals promote, as many free radicals, the decay of β-phycoerythrin fluorescence emission, they oxidize NADH and ascorbic acid and initiate arachidonic acid peroxidation with formation of hydroperoxides and dienes. These results suggest that tyrosyl free radicals generated when tyrosine residues in protein and peptides are activated in vivo by peroxidase-H₂O₂ might undergo the peroxidation of membrane lipids.