Salt-Enhanced Aminolysis of Acyl-α-Chymotrypsins by Dipeptides

Increase in KC1 concentration from 0.1 m to 3 m enhances the chymotrypsin-catalyzed acyl-transfer to a series of dipeptides, H2N-CH(R1)C(O)NHCH(R2)C(O)O, by factors between 15 and 44. The observed positive salt effect seems to be a screening of the unfavorable electrostatic interaction between the dipeptide carboxyl group and a negatively charged area in the S' subsite on the enzyme surface. The effect is of practical use in preparative peptide synthesis-in 3 m KCl solutions the analytical yields of tripeptides of up to 99 per cent have been obtained.