Lysozyme selective cleavage

Tyrosyl and hystidyl peptide bonds, which are usually cleaved by other brominating agents such as NBS, are sensitive to oxidation also but are not cleaved by TBC. Tyrosine was converted by TBC to 3,5-dibromotyrosine, cysteine to cysteic acid, methionine to methionine sulfoxide and tryptophan most probably converted to a bromooxindole derivative. Optimal conditions for the cleavage of the tryptophanyl peptide bond were found to be 3 equiv. of TBC at pH 3 for 5-15 min at room temperature. The model peptide N-carbobenzoxy-tryptophanyl-glycine was cleaved in about 50% yield NBS also cleaved this peptide to the same extent. In lysozyme, selective cleavage of the expected tryptophanyl peptide bonds (yields 5-60%) was obtained. 

Conditions for the selective cleavage of the kyneurenyl bond in ozone-oxidized hen egg white lysozyme in aqueous hydrazine solution have been... 

Conditions for the selective cleavage of the kyneurenyl bond in oxidized hen egg-white lysozyme in aqueous hydrazine solution have been established. Further derivatization and peptide analysis showed that the iV -formylky-nurenine is present at position 62 in place of L-tryptophan in the native protein. 

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