Pro-opiocortin processing in the pituitary: a model for neuropeptide biosynthesis.

The biosynthesis of alpha-MSH, beta-endorphin and ACTH in the pituitary is reviewed. These neuropeptides are synthesized from a common pro-protein, pro-opiomelanocortin. The pro-protein is cleaved intragranularly, at pairs of basic residues in the molecule to yield the respective peptide products. An unique, thiol protease (pro-opiocortin converting enzyme) and a carboxypeptidase B-like enzyme, both localized within pituitary secretory granules and having a pH optimum of 5-6, appear to be involved in the proteolytic processing of pro-opiomelanocortin.