title: Partial purification of somatotropin receptors from pig liver: they arise from a single somatotropin receptor messenger RNA transcript.
abstract: Specific binding sites for porcine somatotropin (pST) have been identified in pig liver microsomal membranes. Little information, however, is available about the size and number of ST receptor (ST-R) forms present. Therefore, the present study was conducted to characterize ST-R in pig liver using two approaches. In the first set of experiments, cross-linking of [125I]bST (bovine ST) to microsomal membranes, followed by gel electrophoresis under reducing conditions, revealed the presence of a predominant protein of 107 kDa and four other proteins of 71, 52, 40, and 26 kDa. In a second set of experiments, ST-R were partially purified using affinity chromatography. Binding studies indicated that there was an approximately 1,800-fold purification compared to liver homogenate. Two specific proteins of 107 and 40 kDa were detected after crosslinking of [125I]bST to partially purified ST-R. Northern blot analysis revealed that these proteins arise by posttranslational modification of a single 4.2-kilobase somatotropin receptor messenger RNA transcript. Although the present study indicates that several forms of ST-R are present in pig liver, it is not clear what physiological role these different ST-R play in mediating the hepatic effects of pST. It is evident, however, that the smaller proteins are generated from the 107-kDa protein, which is the predominant isoform present in liver microsomal membranes.
authors.affiliation: Institut National de la Recherche Agronomique, Station de Recherches Porcines, Saint Gilleś, L'Hermitage, France.
authors.forename: I
authors.initials: I
authors.lastname: Louveau
authors.forename: T D
authors.initials: TD
authors.lastname: Etherton
mesh_terms: D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D015152:Blotting, Northern; D002846:Chromatography, Affinity; D004305:Dose-Response Relationship, Drug; D005260:Female; D013006:Growth Hormone / Q000378:metabolism / Q000494:pharmacology; D008099:Liver / Q000737:chemistry*; D008862:Microsomes, Liver / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000032:analysis*; D011986:Receptors, Somatotropin / Q000235:genetics / Q000302:isolation & purification*; D013552:Swine / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D012333:RNA, Messenger; D011986:Receptors, Somatotropin; D013006:Growth Hormone