Novel Opioid Peptides Derived from Casein (β-Casomorphins). III. Synthetic Peptides Corresponding to Components from Bovine Casein Peptone

Abstract

Six peptides of the .beta.-casomorphin group were synthesized and purified. The peptides proved to be pure as judged by rechromatography on P-2, amino acid analysis and N-terminal amino acid sequence analysis. In confirmation of the success of the synthetic procedure, it was established that synthetic peptides displayed the same biological activity in the guinea pig ileum bioassay as counterparts originally isolated from bovine casein peptone. In addition, the peptides synthesized exhibited only 1 ninhydrin-positive band upon electrophoresis. Concerning the opioid activity, it is apparently of minor importance whether the C-terminus possesses a free carboxyl group or a methyl ester. Amidation of the C-terminus leads to a remarkable increase in opioid potencies of the .beta.-casomorphins.