ISOLATION AND PHOTOOXIDATION OF LYSOZYME FRAGMENTS
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Date
1981
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Abstract
Reduction of the 4 disulfide bonds and further carboxymethylation of lysozyme followed by its reaction with CNBr brings about L-I, (aa [amino acids] 1-12) and L-II-III (aa 13-129) peptides. When breaking the polypeptidic chain by CNBr action and freeing the peptides formed through S-S bonds reduction and carboxymethylation, 3 peptides are obtained corresponding to L-I (aa 1-12), L-II (aa 13-105) and L-III (aa 106-129). L-II-III, L-III and L-II peptides were separately subjected to photo-oxidation in presence of riboflavin in 0.05 M phosphate buffer, pH 7.0. The kinetic analysis of Trp photo-oxidation in L-II-III peptides shows that these residues keep, to a great extent, the degree of exposure they had in native lysozyme. L-II peptide also presents Trp residues with a different degree of exposure. Presence of Tyr photo-oxidation in L-II and L-II-III peptides (this does not take place in native lysozyme) suggests a relationship between photo-oxidation selectivity and the degree of exposure of certain amino acid residues in spatial configuration.