title: Characterization of a macromolecular aggregate of ovine pituitary corticotropin-beta-lipotropin common precursor.
abstract: A macromolecular aggregate of corticotropin-beta-lipotropin common precursor had been observed in ovine pituitary preparations as an excluded fraction of Sephadex G-200 gel filtration. This fraction could not penetrate a 10% gel during sodium dodecyl sulfate-polyacrylamide gel electrophoresis, when 2-mercaptoethanol or other disulfide-cleaving agents were not present in the buffer used to solubilize the protein preparation prior to the electrophoresis. On a 4.6% gel (acrylamide:bisacrylamide, 20:1), the material migrated as a diffuse band to a position between those of beta-galactosidase (Mr 130 000) and myosin (Mr 200 000). Both observations were consistent with an apparent Mr greatly in excess of that of the corticotropin-beta-lipotropin common precursor reported by many investigators. Neither 5% SDS nor 1% Triton X-100 could dissociate the macromolecular aggregate, but 2-mercaptoethanol and urea, either alone or in combination, were able to dissociate it to two main protein components, one of which was identified as corticotropin-beta-lipotropin with an apparent Mr of 34 000. The fact that urea alone could dissociate this macromolecular aggregate led us to believe that it might be a non-covalent aggregate and that 2-mercaptoethanol probably did not achieve the dissociation through the cleavage of an interchain disulfide bond but by bringing about conformational changes as a result of reduction of intrachain disulfide bonds so that aggregation became unfavorable. Moreover, the dissociation by urea or by 2-mercaptoethanol was found to be irreversible. The origin of the macromolecular aggregate of corticotropin-beta-lipotropin common precursor remains obscure.
mesh_terms: D000324:Adrenocorticotropic Hormone / Q000032:analysis; D000818:Animals; D002850:Chromatography, Gel; D004220:Disulfides / Q000032:analysis; D046911:Macromolecular Substances; D008623:Mercaptoethanol; D008970:Molecular Weight; D010902:Pituitary Gland / Q000032:analysis*; D010908:Pituitary Hormones, Anterior / Q000302:isolation & purification*; D011333:Pro-Opiomelanocortin; D011498:Protein Precursors / Q000302:isolation & purification*; D011863:Radioimmunoassay; D012756:Sheep; D008083:beta-Lipotropin / Q000032:analysis
chemical_list: D004220:Disulfides; D046911:Macromolecular Substances; D010908:Pituitary Hormones, Anterior; D011498:Protein Precursors; D008623:Mercaptoethanol; D011333:Pro-Opiomelanocortin; D000324:Adrenocorticotropic Hormone; D008083:beta-Lipotropin