FORMATION OF O-TYROSINE AND DITYROSINE IN PROTEINS DURING RADIOLYTIC AND METAL-CATALYZED OXIDATION

To evaluate their usefulness as chemical indicators of cumulative oxid ative damage to proteins, we studied the kinetics and extent of format ion of ortho-tyrosine (o-Tyr), dityrosine (DT), and dityrosine-like fl uorescence (E(x) = 317 nm, E(m) = 407 nm) in the model proteins RNase and lysozyme exposed to radiolytic and metal-catalyzed (H2O2/Cu2+) oxi dation (MCO). Although there were protein-dependent differences, o-Tyr , DT, and fluorescence increased coordinately during oxidation of the proteins in both oxidation systems. The contribution of DT to total di tyrosine-like fluorescence in oxidized proteins varied from 2-100%, de pending on the protein, type of oxidation, and extent of oxidative dam age. In proteins exposed to MCO, DT typically accounted for >50% of th e fluorescence at DT wavelengths. These studies indicate that o-Tyr an d DT should be useful chemical markers of cumulative exposure of prote ins to MCO in vitro and in vivo.