The cross-linking of tyrosine residues in apo-ovotransferrin by treatment with periodate anions

The iron-binding ability of apotransferrins is rapidly abolished in the reaction with periodate anions, which destroys 4 mol of tyrosine per mol of protein. Treatment of ovotransferrin with cyanogen bromide and tryptic digestion of the glycopeptide fragment demonstrated the existence of an intramolecular cross-link in the C-terminal domain of the oxidized protein. The cross-linked residues were identified as Tyr-421 and Tyr-524 and the product is similar in structure to 3,3′-dityrosine.