Photo-oxidation, sensitized by proflavin, of a number of protein constituents

The proflavine-sensitized photo-oxidation of tryptophan, tyrosine, histidine and methionine, as well as of oxidized glutathione, was studied. The pH of the reaction mixture was found to have a profound influence on the oxidation rate. At pH 3–4, only tryptophan and methionine are oxidized. At pH 6–7 tryptophan, methionine and histidine, and at pH 8 all four amino acids, are oxidized. Oxidized glutathione is scarcely oxidized any further in the whole pH range investigated. The applicability of proflavine-sensitized photo-oxidation to the selective modification of proteins is discussed