Zeggari M, Viguerie N, Susini C, Esteve J P, Vaysse N, Rivier J, Wunsch E, Ribet A
Peptides. 1986 Nov-Dec;7(6):953-9. doi: 10.1016/0196-9781(86)90120-8.
Somatostatin binding to guinea pig pancreatic acinar cell plasma membranes was characterized with an iodinated stable analog of somatostatin 28 (S28): 125I-[Leu8,DTrp22,Tyr25]S28. The binding was highly dependent on calcium ions. In 0.2 mM free Ca2+ medium, binding at 37 degrees C was saturable, slowly reversible and exhibited a single class of high affinity binding sites (KD = 0.05 +/- 0.01 nM, Bmax = 157 +/- 33 fmol/mg protein). Dissociation of bound radioactivity occurred with biphasic kinetics. Rate of dissociation increased when dissociation was measured at a time before equilibrium binding was reached. In 30 nM free Ca2+ medium, binding affinity and maximal binding capacity were decreased by about 4-fold. Decreasing calcium concentrations increased the amount of rapidly dissociating form of the receptor. Somatostatin 14 antagonist, Des AA1,2[AzaAla4-5,DTrp8, Phe12-13]-somatostatin was active at the membrane level in inhibiting the binding. We conclude that using 125I-[Leu8,DTrp22,Tyr25]S28 as radioligand allows us to characterize a population of specific somatostatin receptors which are not different from those we previously described with the radioligand 125I-[Tyr11]-somatostatin. Somatostatin receptors could exist in two interconvertible forms. Calcium ions are an essential component in the regulation of the conformational change of somatostatin receptors.
用生长抑素28（S28）的碘化稳定类似物：125I-[Leu8,DTrp22,Tyr25]S28对豚鼠胰腺腺泡细胞质膜上生长抑素的结合特性进行了研究。该结合高度依赖于钙离子。在0.2 mM游离Ca2+培养基中，37℃时的结合是可饱和的、缓慢可逆的，并表现出一类高亲和力结合位点（KD = 0.05 +/- 0.01 nM，Bmax = 157 +/- 33 fmol/mg蛋白质）。结合放射性的解离呈双相动力学。在达到平衡结合之前的某个时间测量解离时，解离速率增加。在30 nM游离Ca2+培养基中，结合亲和力和最大结合容量降低了约4倍。降低钙浓度增加了受体快速解离形式的量。生长抑素14拮抗剂，去氨基AA1,2[氮杂丙氨酸4-5，DTrp8，苯丙氨酸12-13]-生长抑素在膜水平上具有抑制结合的活性。我们得出结论，使用125I-[Leu8,DTrp22,Tyr25]S28作为放射性配体使我们能够表征一群特定的生长抑素受体，这些受体与我们之前用放射性配体125I-[Tyr11]-生长抑素描述的受体没有区别。生长抑素受体可能以两种可相互转化的形式存在。钙离子是调节生长抑素受体构象变化的重要组成部分。
