碘化人類生長激素與雌鼠肝臟細胞膜上之受體之專一性結合及聯結

Abstract

摘要 碘化人類生長激素(125I-hGH)對雌鼠肝臟微小體膜(female rat liver microsomal membranes)有專一性及飽和性之結合。此種結合受時間、溫度及pH之影響，而且與膜蛋白質之濃度呈函數關係。豬激乳素(porcine prolactin)可抑制此125I-hGH與肝臟細胞膜之結合，豬生長激素則否。此結果顯示125I-hGH絕大多數是與泌乳結合位置(lactogenic binding sites)亦即激乳素受體(prolactin receptors)結合。Scatchard plot分析呈直線，亦顯示此為單一結合位置。以disuccinimidyl suberate(DSS)或ethylene glycol bis-succinimidyl succinate (EGS)處理，則專一性結合之125I-hGH可與細胞膜蛋白質聯結，將這些蛋白質以SDS gel electrophoresis展開，結果產生三條具有放射性之bands(分子量相當於41，66及126Kdal)，在沒有DSS或EGS，或者有大量未碘化hGH存在下，並無此結果。由這些資料顯示hGH(21Kdal)與20，45及105Kdal之勝?聯結。這些勝?可能是激乳素受體之次單元(subunits)。

Abstract 125I-hGH was found to show specific and saturable binding to the liver microsomal membranes of the female rat, which was time, temperature and pH dependent and was a function of concentration of membrane protein. It was shown that porcine prolactin but not porcine growth hormone can inhibit the binding of 125I-hGH to the liver membranes. This result suggested that 125I-hGH bind almost exclusively to the lactogenic binding sites (or prolactin receptors). Scatchard analysis produced a linear plot also suggested the presence of single class of binding sites. When treated with DSS or EGS, the specifically bound hGH was cross-linked to membrane proteins. SDS gel electrophoresis revealed three bands of radioactivity (Mr=41,000, 66,000, and 126,000) that were not seen in controls lacking DSS (or EGS) or in the presence of large amount of cold hGH. These data indicated that hGH (Mr=21,000) was cross-linked to peptides of 20, 45, and 105Kdal. These peptides may be the subunits of prolactin receptors.