title: In vitro processing of proopiomelanocortin by recombinant PC1 (SPC3).
abstract: The prohormone convertases, PC1 (SPC3) and PC2, are subtilisin-like serine proteases capable of processing neuropeptide precursors. In cotransfection experiments, other investigators have found that PC1 and PC2 can process POMC to appropriate peptide products. In this study, recombinant rat PC1 was stably expressed in a mouse L-cell line and partially purified. Mouse POMC was cleaved by recombinant PC1 to generate ACTH intermediates, ACTH, ACTH linked to joining peptide, joining peptide, 16-kilodalton N-POMC, N-POMC-(1-74), and beta-lipotropin. Recombinant PC1 was also found to cleave ACTH to ACTH-(1-15) and bovine N-POMC-(1-77) to gamma 3 MSH. The pH optimum of the cleavages was 6.0. We conclude that recombinant PC1 is capable of processing POMC in vitro at all of the paired basic residues, with the exception of Lys-Arg and Lys-Lys in beta-lipotropin and beta-endorphin, respectively. This in vitro study showed a more general specificity of recombinant PC1 for paired and tetrabasic residues of POMC than was previously found in cotransfection experiments. Other cellular regulatory mechanisms probably play a role in limiting the processing of POMC in vivo in the anterior pituitary, where gamma 3 MSH and alpha MSH are not found in significant amounts.
authors.affiliation: Section on Cellular Neurobiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: T C
authors.initials: TC
authors.lastname: Friedman
authors.forename: Y P
authors.initials: YP
authors.lastname: Loh
authors.forename: N P
authors.initials: NP
authors.lastname: Birch
mesh_terms: D000324:Adrenocorticotropic Hormone / Q000378:metabolism; D000818:Animals; D016282:Aspartic Acid Endopeptidases / Q000378:metabolism / Q000494:pharmacology*; D002460:Cell Line; D003470:Culture Media / Q000494:pharmacology; D051379:Mice; D010446:Peptide Fragments / Q000378:metabolism; D011333:Pro-Opiomelanocortin / Q000378:metabolism*; D045664:Proprotein Convertase 1; D043484:Proprotein Convertases; D011499:Protein Processing, Post-Translational / Q000187:drug effects*; D051381:Rats; D011994:Recombinant Proteins
chemical_list: D003470:Culture Media; D010446:Peptide Fragments; D011994:Recombinant Proteins; C028182:proopiocortin fragments; D011333:Pro-Opiomelanocortin; D000324:Adrenocorticotropic Hormone; D043484:Proprotein Convertases; C473656:Pcsk1 protein, mouse; D045664:Proprotein Convertase 1; D016282:Aspartic Acid Endopeptidases