title: Biosynthesis and processing of the N-terminal part of proopiomelanocortin in Xenopus laevis: characterization of gamma-MSH peptides.
abstract: The aim of this study was to determine the terminal products of processing of the N-terminal part of proopiomelanocortin (POMC) in pituitary melanotrope cells of Xenopus laevis. Biosynthetic in vitro labelling studies showed that POMC is rapidly processed to form N-terminal peptides with an estimated molecular mass of 18 kDa, 9 kDa and 4 kDa. All peptides were released into the medium, indicating that they are processing end products. An antiserum was raised against the synthetic N-terminal eight amino acids of the putative Xenopus gamma-MSH which is present in the N-terminal part of POMC. With immunocytochemistry we demonstrated that gamma-MSH-immunoreactive material in the pituitary gland is restricted to the pars intermedia. A radioimmunoassay in combination with reversed-phase HPLC revealed the presence of at least two gamma-MSH-like peptides. Complete purification followed by electrospray ionization mass spectrometry and amino acid sequence determination showed that these peptides are gamma 1-MSH and glycosylated gamma 3-MSH. The amounts of these gamma-MSH peptides were low compared to the other POMC-derived peptides, alpha-MSH and beta-endorphin. Only 10% of POMC is processed into gamma-MSH peptides and the 4 kDa peptide, leaving the 18 kDa and 9 kDa peptides as the major end products.
authors.affiliation: Department of Cellular Animal Physiology, Nijmegen Institute for Neurosciences, Faculty of Science, University of Nijmegen, The Netherlands.
authors.forename: F J
authors.initials: FJ
authors.lastname: van Strien
authors.forename: B
authors.initials: B
authors.lastname: Devreese
authors.forename: J
authors.initials: J
authors.lastname: Van Beeumen
authors.forename: E W
authors.initials: EW
authors.lastname: Roubos
authors.forename: B G
authors.initials: BG
authors.lastname: Jenks
mesh_terms: D000222:Adaptation, Physiological; D000595:Amino Acid Sequence; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D006031:Glycosylation; D013058:Mass Spectrometry; D009074:Melanocyte-Stimulating Hormones / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010446:Peptide Fragments / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D010902:Pituitary Gland / Q000737:chemistry / Q000187:drug effects; D011333:Pro-Opiomelanocortin / Q000737:chemistry / Q000378:metabolism*; D011863:Radioimmunoassay; D017421:Sequence Analysis; D014415:Tunicamycin / Q000494:pharmacology; D014982:Xenopus laevis
chemical_list: D010446:Peptide Fragments; D014415:Tunicamycin; D011333:Pro-Opiomelanocortin; D009074:Melanocyte-Stimulating Hormones