Specificity of pepsin-catalyzed peptide bond synthesis

The rates of the pepsin-catalyzed synthesis of oligopeptides of the general type A-Phe-Leu-B by the condensation of A-Phe-OH with H-Leu-B have been determined by means of analytical high performance liquid chromatography. Variation of the A group led to large changes in the initial rates of the condensation reaction, and the effect of such changes was found to be similar to that previously found for the secondary specificity of pepsin in the hydrolysis of oligopeptide substrates. Replacement of the Phe and Leu residues of A-Phe-OH or H-Leu-B by other amino acid residues gave relative rates of synthesis in accord with the known primary specificity of the hydrolytic action of pepsin. Partially-acetylated pepsin, which exhibits enhanced hydrolytic activity, also catalyzed the condensation reaction more effectively. The results are discussed in relation to the potential utility and limitations of pepsin as a catalyst in the preparative synthesis of oligopeptides and to the problem of the mechanism of its action.