Studies on Changes of Protein by Dye Sensitized Photooxidation

Abstract

Photooxidation products of amino acid residues of lysozyme were identified as kynurenine and 3-oxykynurenine from tryptophan, alanine from histidine, methionine sulfoxide and methionine sulfone from methionine, cysteic acid from cystine, glutamic acid from arginine and serine from tyrosine by isolating peptides in tryptic hydrolysate, although the yield of each product did not always reach 100%.

Higher intensity of incident rays caused breakage of peptide chain, the mechanism of which was divided into two steps; the first predominated at the earlier stage of illumination with oxidation of tryptophan, the second predominated at the later stage of illumination accompaning the formation of amide and α-keto acid groups.

Carbonyls and peroxides liberated during illumination were also determined.