FROM BETA-LIPOTROPIN TO BETA-ENDORPHIN AND PRO-OPIO-MELANOCORTIN

Studies on the biosynthesis of β-LPH on the one hand, and of ACTH on the other, have produced a new concept, that of a single precursor form which contains three active molecules. Thus, it is proper to name such a precursor 'pro-opio-melanocortin'. The concept that β-LPH was a precursor molecule was first put forward in 1967 and was based on both structural forms and biological activities. The discovery that morphine-like substances are part of the C-terminal fragment of β-LPH brought an additional important biological side product. That, together with the recent demonstration of ACTH as part of a still larger precursor, constitutes an exciting model for the study of peptide hormone biosynthesis. The authors have shown unambiguously that β-endorphin is the result of a maturation process from the large precursor, while β-LPH is an important and transient intermediary. Since it is also present in the brain, the recent results using pars intermedia cells can be applied to study the fabrication and degradation of these molecules in the brain. The authors expect to see it established that all other neuropeptides are also biosynthesized as larger precursor molecules whose structure at the site of cleavage could well be constituted of two basic amino acids like in the pro-opio-melanocortin.