The effect of non-coded amino acids on the degradation of oxytocin analogs with α-chymotrypsin

Abstract

Oxytocin and a series of its analogs, containing a non-coded amino acid in the carboxy-terminal linear part, were incubated with α-chymotrypsin and their degradation was monitored using high performance liquid chromatography (HPLC). Degradation of the analogs was markedly slower than that of oxytocin, its rate depending on the structure of the amino acid in position 8. Whereas in oxytocin the cleavage takes place at the leucine-glycine peptide bond in its carboxy-terminal moiety, no cleavage at this position was observed in the analogs; these were cleaved only at the tyrosine-isoleucine bond in the cyclic part. The same type of cleavage was observed in analog with a disulfide bond in the C-terminal oxytocin tripeptide. The degradation sites in oxytocin and its analogs were determined using the amino acid and sequentional analysis of the products isolated from the incubation mixture by preparative HPLC.