Enhancement of cyanogen bromide cleavage yields for methionyl-serine and methionyl-threonine peptide bonds.

Cyanogen bromide (CNBr) is a common chemical used to hydrolyze peptide bonds C-terminal to methionine residues in peptides and proteins. In most cases, the efficiency of this bond cleavage is greater than 90% except in situations where a serine or threonine residue follows methionine in the amino acid sequence. We have explored the mechanism of the methionyl-serine and methionyl-threonine CNBr cleavage inefficiencies and have developed a simple methodology to more than double cleavage yields relative to standard literature conditions. This method entails increasing the concentration of water during the cleavage reaction either by reducing the formic acid concentration or by performing the cleavage in an acidic aqueous medium. This approach provides a more desirable methodology from the perspective of enhanced yields and greater ease of handling in cases of large-scale use. Copyright 1999 Academic Press.