PROGRESS IN NON-ENZYMATIC SELECTIVE MODIFICATION AND CLEAVAGE OF PROTEINS

Abstract

This chapter discusses the progress in nonenzymatic selective modification and cleavage of proteins. Cyanogen bromide cleaves methionyl bonds in acidic medium in high yields with practically no side reactions. Cleavage of the four methionyl bonds in ribonuclease proceeds in yields up to 85–95%. Gel filtration permits the isolation of an N-terminal 13-unit peptide, free homoserine, and the core. Cyanogen bromide cleavage of sperm whale myoglobin, containing two methionine residues, followed by gel filtration on Sephadex GS-25 and GS-75, has led to the isolation of three peptides in high yield. N-bromosuccinimide and N-bromoacetamide can be used for the selective cleavage of C-tryptophyl and C-tyrosyl bonds and for the selective oxidation of indole to oxindole residues. Tryptophan residues of chymotrypsin are more accessible to oxidation than in di-isopropyl-phosphoryl-chymotrypsin. The difference spectrum of DIP-chymotrypsin (one tryptophan oxidized) versus chymotrypsin (one tryptophan oxidized) is identical with the difference spectrum of DIP-chymotrypsin versus chymotrypsin.