Chemical cleavage of proteins in solution.

Described in this unit are five basic protocols that are widely used for specific and efficient chemical cleavage of proteins in solution. Cyanogen bromide (CNBr) cleaves at methionine (Met) residues; BNPS-skatole cleaves at tryptophan (Trp) residues; formic acid cleaves at aspartic acid-proline (Asp-Pro) peptide bonds; hydroxylamine cleaves at asparagine-glycine (Asn-Gly) peptide bonds, and 2-nitro-5-thiocyanobenzoic acid (NTCB) cleaves at cysteine (Cys) residues. Because the above loci are at relatively low abundance in most proteins, digestion with these agents will yield relatively long peptides.