PHARMACOLOGICAL AND IMMUNOLOGICAL CHARACTERIZATION OF THE LEU5 ANALOG OF HUMAN BETA-ENDORPHIN

The potencies of βh-endorphin, Met (O)5-βh-endorphin, and synthetic Leu5-βh-endorphin have been compared in three bioassays of opioid activity, and in two radioimmunoassays. In all assays, a peptide isolated from hemodialysates from a psychotic patient behaved like Leu5-βh-endorphin; it has been distinguished unambiguously from βh-endorphin and Met(O)5-βh-endorphin. Leu5-βh-endorphin was one-fifth as potent as βh-endorphin in guinea pig ileum myenteric plexus, but was only slightly less active in mouse vas deferens and in guinea pig brain opiate receptor binding assay. The low cross-reactivity of Leu5-βh-endorphin relative to βh-endorphin with an antiserum raised to β-endorphin suggests that the preferred solution conformations of these peptides are different. In all bioassays βh-endorphin was 2- to 3-fold less potent than βc-endorphin. © 1979.