Studies on peptide amidase-catalysed C-terminal peptide amidation in organic media with respect to its substrate specificity

Peptide amidase-catalysed amidations of the C- terminal carboxylic group of peptides were studied using model substrates of a large series of N(alpha)-protected di-, tri-, tetra- and penta-peptides in the presence of NH4HCO3 as the ammonium source. The maximal yields of amide syntheses were achieved in a medium consisting of acetonitrile with 20-25 vol% of dimethylformamide and 3 vol% of water. Under these conditions, the substrate specificity of the enzyme was more restricted in the synthetic reaction than was found for the amide hydrolysis. Elongation of the peptide chain had a negative effect on enzymic amidation. Thus the direct amidation of N(alpha)-t-butoxycarbonyl-protected Leu-enkephalin resulted in a low yield of protected enkephalin amide.