Thermolysin catalyzed semisynthesis of peptide hormones by introduction of Phe-NH2 or Tyr-NH2 at the carboxyl termini.

The semisynthesis of C-terminal peptides of gastrin, calcitonin gene-related peptides (rat and human), and cholecystokinin, or of human neuropeptide Y was achieved by introduction of Phe-NH2 or Tyr-NH2 at their carboxyl termini, respectively. Thermolysin or the related enzyme was used for the purpose. The coupling was usually performed in the presence of high concentration of organic cosolvent, where the secondary hydrolysis was negligibly small.