Kinetic studies on the mechanism and the specificity of peptide semisynthesis catalyzed by the serine proteases alpha-chymotrypsin and beta-trypsin.

The mechanism of peptide semisynthesis catalyzed by alpha-chymotrypsin and beta-trypsin has been investigated. The dependence of the apparent ratio of the second order rate constants for the deacylation of the acyl-enzyme intermediate by water and other nucleophiles (amino acid amides) on the nucleophile concentration indicates a mechanism that involves two acyl-enzymes. One with and one without bound nucleophile that both can be deacylated by water. The nucleophile specificity in peptide semisynthesis catalyzed by the proteases was found to reflect the P1-specificity in the corresponding hydrolytic reaction.