ABSTRACT
Several procedures are available for limited hydrolysis of a peptide chain. Most of these are enzymatic methods of varying specificities, but one important, highly specific chemical method is also widely used, namely treatment with cyanogen bromide (CNBr). CNBr reacts specifically on the carboxyl side of a methionine-containing peptide, cleaving the chain between methionine and the next amino acid and converting methionine to homoserine lactone. As is usually the case, individual fragments are isolated, and each is subjected to complete hydrolysis in preparation for amino acid analysis. Elastase functions in a manner analogous to trypsin and chymotrypsin, cleaving on the carboxyl side of its target amino acids. Pepsin will digest proteins by catalyzing hydrolysis of peptide bonds involving leucine, the aromatic amino acids, or the acidic amino acids, but not their amides. Peptic digestion of a peptide with the amino acid composition gives two products. One product contains only isoleucine, while the other contains isoleucine and phenylalanine.
