Mitra S P, Carraway R E
Physiology Department, University of Massachusetts Medical Center, Worcester 01655, USA.
Peptides. 1995;16(3):471-7. doi: 10.1016/0196-9781(94)00215-r.
Using 125I-labeled neurotensin (NT), chicken liver was found to contain high affinity, G-protein-linked receptors directed specifically towards the bioactive C-terminal portion of NT. Binding was proportional to membrane and optimal at pH 7.5. The apparent Kd (approximately 91 pM) for this single class of binding sites was similar to Kds reported for the high-affinity components of NT binding to mammalian brain and intestinal membranes. However, the binding capacity (Bmax, approximately 2.3 pmol/mg) was 10-100 times higher than values reported for these mammalian tissues. Binding was inhibited by GTP analogues and by treatment with pertussis toxin but not by cholera toxin. Treatments with alkaline solutions, shown to inactivate G-proteins, decreased subsequent binding at pH 7.5. Whereas low concentrations of Mg2+ (optimum, approximately 0.5 mM) enhanced NT binding, concentrations of 5 mM and above were inhibitory. Cross-linking of 125I-labeled NT to liver membranes using glutaraldehyde specifically labeled two substances of approximately 52 and approximately 90 kDa, which could represent different binding proteins or complexes. These data demonstrate the presence in chicken liver of large amounts of high-affinity NT receptor(s) coupled to pertussis toxin-sensitive G-protein(s).
使用125I标记的神经降压素（NT），发现鸡肝含有高亲和力、与G蛋白偶联的受体，该受体特异性地针对NT的生物活性C末端部分。结合与膜成正比，在pH 7.5时最佳。这类单一结合位点的表观解离常数（约91 pM）与报道的NT与哺乳动物脑和肠膜结合的高亲和力成分的解离常数相似。然而，结合能力（最大结合量，约2.3 pmol/mg）比这些哺乳动物组织报道的值高10 - 100倍。GTP类似物和百日咳毒素处理可抑制结合，但霍乱毒素无此作用。用碱性溶液处理可使G蛋白失活，降低随后在pH 7.5时的结合。低浓度的Mg2+（最佳浓度约0.5 mM）增强NT结合，而5 mM及以上浓度则具有抑制作用。使用戊二醛将125I标记的NT与肝膜交联，特异性标记了两种分子量约为52 kDa和约90 kDa的物质，它们可能代表不同的结合蛋白或复合物。这些数据表明鸡肝中存在大量与百日咳毒素敏感的G蛋白偶联的高亲和力NT受体。
