27] The cyanogen bromide reaction

Abstract

This chapter discusses the applications of the cyanogens bromide reaction. Cyanogen bromide is capable of cleaving thioethers. The action of cyanogen bromide upon proteins is unique in its selective attack on methionine. The reaction of methionine with cyanogen bromide is greatly facilitated by the strong neighboring group effect exerted by the carboxyl group. Cyanogen bromide is synthesized from bromine and potassium cyanide. The selectivity of the reaction of cyanogen bromide with amino acids depends on pH. The selectivity of the cyanogen bromide reaction is demonstrated by exposure to cyanogen bromide of a standard mixture of amino acids, as is used for calibration purposes in automated amino acid analyzer systems. A number of applications to the general structural elucidation of peptides and proteins are: ribonuclease, rabbit γ-globulin, and chymotrypsin. The reaction is applied in many other instances and is useful in a number of ways, such as in the structural elucidation of peptides and proteins, the detection of multiple forms of enzymes and of oxidized residues of methionine, the preparation of physiologically active peptide fragments, the location of newly introduced cross-linkages in enzymes,and the identification and characterization of fragments from enzyme active sites.