Biosynthesis of pro-opiomelanocortin-derived peptides in the mouse neurointermediate lobe

This report concerns biosynthetic studies conducted with neurointermediate lobes of the mouse pituitary gland. High performance liquid chromatography was used to resolve newly synthesized peptides after in-vitro incubation of lobes with radioactive amino acids. Among the newly synthesized peptides identified were alpha-MSH, des-N alpha-acetyl-alpha-MSH, two forms of corticotrophin-like intermediate lobe peptide and beta-endorphin. The biosynthesis of a glycosylated gamma 3-MSH-like peptide was also demonstrated. While no newly synthesized beta-MSH could be identified, a peptide designated gamma-lipotrophin was found. Pulse-chase analysis revealed that the major biosynthetic pathway leading to the production of alpha-MSH involved the acetylation of the des-acetyl form of this peptide. Furthermore, it was evident that newly synthesized beta-endorphin was largely converted to modified forms of this peptide; most of the terminal product was probably N-acetylated endorphin.