Selective Oxidation of Tryptophan and Histidine Residues in Protein through the Copper-catalyzed Autoxidation of l-Ascorbic Acid

Abstract

The oxidative modification of bovine serum albumin with an ascorbic acid-copper ion system was studied. Under physiological conditions (pH 7.2, ambient temperature), this system mainly caused the modification of amino acid residues in the protein, and its polymerization was scarcely observed. The results of spectrophotometry assays and amino and analysis of the protein clearly suggested the selective damage to tryptophan and histidine residues. The reaction could be retarded by catalase and Cu(II)-chelating agents, while superoxide dismutase and hydroxyl radical scavengers showed little effect. These specific reactions were explained by the site-specific formation of the oxygen-derived free radical followed by its reaction with a specific site of the protein.