Evidence for peptide synthesis in the course of in vitro proteolysis

The present paper reports on studies concerned with furnishing evidence for peptide synthesis in the course of in vitro proteolysis. To this end, the oxidized chain B from insulin (INS) (S = 5% in demineralized water) was subjected to tryptic proteolysis (E/S = 1/50; pH 5; 37 degrees C; 24 h). HPLC-as well as amino acid-and sequence analytical studies have shown that the heptapeptide INS 23-29 (Gly-Phe-Phe-Tyr-Thr-Pro-Lys) liberated by way of hydrolysis is linked by tryptic synthesis via transpeptidation or condensation to form a dimer which accounts for 15% of the amount of monomer. The results of the model trials show clearly that during in vitro proteolysis chemical reactions beyond hydrolytic cleavage of peptide bonds take place. In principle, plastein-like reactions (transpeptidation, condensation) can occur during each in vitro proteolysis.