Thermolysin-catalyzed peptide bond synthesis.

Abstract

The rates of the thermolysin-catalyzed synthesis of peptides were determined by means of HPLC [high performance liquid chromatography]. In the condensation of various N-substituted amino acids and peptides with L-leucinanilide, the enzyme exhibits preference for a hydrophobic L-amino acid as the donor of the carbonyl group of the newly formed bond. The presence of another hydrophobic amino acid residue adjacent to the carbonyl-group donor markedly enhances the rate of synthesis. In general, the effect of structural changes in both the carboxyl and amine components of the condensation reaction is in accord with the available data on the primary and secondary specificities of the thermolysin-catalyzed hydrolysis of oligopeptide substrates. A kinetic study of the condensation of benzyloxycarbonyl-L-phenylalanine with various amine components gave data on the apparent kcat and Km values for the entry of the acidic component into the condensation reaction. The results are consistent with the behavior of rapid-equilibrium random bireactant systems leading to ternary enzyme-substrate complexes, with a synergistic effect in the binding of the 2 reactants at the active site. Because the changes in the apparent Km for the entry of the same acidic component into reaction with different amine components are greater than those in the apparent Km, this synergism is probably largely expressed at the level of the transition-state complex.