Restriction of the specificities of trypsin and alpha-chymotrypsin at a high alkaline pH value

The specificities of trypsin and alpha-chymotrypsin at high alkaline pH values were investigated using dynorphin A and angiotensin I, respectively, as substrates, Under restricted conditions at pH 12.8, trypsin cleaved the Arg-X bonds (X not equal Pro) selectively without cleaving the Lys-X bonds, and alpha-chymotrypsin cleaved the Phe-X bond selectively without cleaving the Tyr-X bond. Therefore, trypsin and alpha-chymotrypsin may be generally useful for selective cleavages of Arg-X bonds and Phe-X bonds, respectively, at such a high pH value at which Lys and Tyr residues are unprotonated.