Chymotrypsin-catalyzed peptide synthesis: kinetic analysis of the kinetically controlled peptide-bond formation

The kinetics of peptide-bond formation catalyzed by δ-chymotrypsin has been studied for a number of peptide products of different length using fixed concentrations of the acyl component (Ac-Phe-OMe. Ac-Ala-Ala-Phe-OMe, or Ac-Ala-Ala-Tyr-OMe) and varying concentration of the amino component (H-Ala-NH2 or H-Ala-Ala-NH2). The time course of the reactions was followed by monitoring ester consumption and peptide product formation by analytical HPLC. On the basis of a plausible four-centre mechanistic model, the theoretical time course of these reactions was calculated using rate and equilibrium constants determined by separate kinetic experiments. The excellent agreement observed between the theoretical and the experimental time courses supports the proposed mechanism and provides evidence for the validity of the present kinetic approach. By focusing attention on the rate constants which are critical for efficient synthesis, this mechanistic information constitutes a valuable basis for the use of the enzymatic peptide synthesis in preparative applications.