title: Characterization of sulfated forms of the pro-opiomelanocortin amino-terminal glycopeptide in rat intermediate lobe cells.
abstract: Explants of rat neurointermediate lobes were incubated in the presence of radioactive amino acids, sugars or sulfate and the labeled proteins were separated by two-dimensional gel electrophoresis. A double series of acidic peptides (Mr = 16,000-21,500) were identified as variant forms of the amino-terminal glycopeptide of pro-opiomelanocortin (N-POMC). The series of peptides with the higher molecular weights (Mr = 18,000-21,500) contain a tryptic fragment (tentatively identified as the tryptic peptide of the "joining peptide": sequence 77 to 93 of rat POMC) which is absent from the forms of the lower molecular weight series (Mr = 16,000 to 18,000). Pulse-chase studies further showed that the high molecular weight forms of N-POMC could be post-translationally cleaved albeit slowly into the species of Mr = 16,000-18,000 which constitute, at least in part, the final maturation products of the N-terminal region of the precursor molecule. All the variant forms of the N-POMC glycopeptide could be labeled with [35S]sulfate. Our results strongly suggest that most of the sulfate groups are attached to N-linked oligosaccharide side chains of N-POMC. We therefore propose that one of the final maturation products of the N-terminal portion of POMC in rat intermediate lobes is a sulfated glycopeptide (Mr = 16,000-18,000) composed of the 1-74 sequence of rat POMC.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D009924:Organ Culture Techniques; D010446:Peptide Fragments / Q000096:biosynthesis* / Q000302:isolation & purification; D010449:Peptide Mapping; D010904:Pituitary Gland, Posterior / Q000378:metabolism*; D011333:Pro-Opiomelanocortin / Q000096:biosynthesis* / Q000302:isolation & purification; D051381:Rats; D013431:Sulfates / Q000378:metabolism; D013462:Sulfur Radioisotopes; D014357:Trypsin
chemical_list: D010446:Peptide Fragments; D013431:Sulfates; D013462:Sulfur Radioisotopes; C031562:pro-opiomelanocortin amino-terminal glycopeptide; D011333:Pro-Opiomelanocortin; D014357:Trypsin