STRUCTURE AND FUNCTION OF GH RECEPTORS AND OF CLEAVED GH

最近的证据表明，生长激素受体（GHR）在兔 肝质膜在结构上不同于微粒体膜中的GHR， 尽管后者受体也以高亲和力结合GH。 晚一步 在GHR的合成中，可能发生在高尔基体或质膜中， 似乎涉及通过二硫键连接亚基。 质膜GHR在功能上也可能不同，因为大部分GHR在质膜中表达。 GH与这些受体结合，但不与微粒体受体结合， 在大二硫环中经历了特异性切割。 分裂激素 似乎以高于完整GH的亲和力结合。 确定二硫化物在哪个亚细胞器中形成 键发生，GHR在质膜和高尔基体部分（轻， 将通过将受体交联到 [125 I] I'm sorry. 各种膜制备物的纯度将通过以下方式进行判断： 酶测定和电子显微镜检查。 质膜和微粒体GHR 将使用常规技术和各种亲和性纯化 色谱柱，包括采用作为偶联物质的柱 GRH特异性单克隆抗体。 单个亚单位来自 纯化的GHR将根据大小，等电点， GH的结合和与单克隆抗体的反应性。 纯化GHR 和膜部分将用于确定GHR的激活是否 刺激膜蛋白的磷酸化，包括 GHR的自磷酸化。 如果能够证明磷酸化， 然后，该终点将用于检查以下结构要求： 受体激活 GHR在切割GH分子中的作用将 使用质膜和纯化的GHR进行检查。 裂解的活性 与受体结合并刺激生物反应的激素 将与完整的激素进行比较。 尽管有无数的研究，GHR的功能和 生物活性GH知之甚少。 然而，最近的事态发展 为全面研究GHR提供了必要的工具 结构和功能。 这项研究将提供有价值的信息， 受体在介导GH作用中的作用;因此，它应该 提供了对生长障碍的新见解， 可归因于GH或GH结合位点的缺陷。

Recent evidence suggests that growth hormone receptors (GHR) in rabbit liver plasmalemma differ structurally from GHR in microsomal membranes, although the latter receptors also bind GH with high affinity. A late step in synthesis of the GHR, possibly occurring in the Golgi or plasmalemma, appears to involve a linking of subunits via a disulfide bond. Plasmalemmal GHR also may differ functionally in that a large proportion of the GH bound to these receptors, but not to microsomal receptors, has undergone a specific cleavage in the large disulfide loop. Cleaved hormone appears to be bound with an affinity higher than that for intact GH. To determine in which subcellular organelle(s) formation of the disulfide bond occurs, GHR in plasmalemma and in Golgi fractions (light, intermediate, heavy) will be examined by crosslinking the receptor to [125I] GH. The purity of various membrane preparations will be judged by enzyme assays and electron microscopy. Plasmalemmal and microsomal GHR will be purified using conventional techniques and various affinity chromatography columns, including a column employing as the coupled species a monoclonal antibody specific for the GRH. Individual subunits from purified GHR will be characterized according to size, isoelectric point, binding of GH and reactivity with the monoclonal antibody. Purified GHR and membrane fractions will be used to determine if activation of the GHR stimulates phosphorylation of membrane proteins, including autophosphorylation of the GHR. If phosphorylation can be demonstrated, then this endpoint will be used to examine the structural requirements for receptor activation. The role of the GHR in cleaving the GH molecule will be examined using plasmalemmal and purified GHR. The activity of cleaved hormone at binding to receptors and in stimulating a biological response will be compared to that of intact hormone. Despite innumerable studies, the function of the GHR and the nature of biologically active GH are poorly understood. However, recent developments have provided the tools necessary for a comprehensive study of GHR structure and function. This study will contribute valuabel information on the role of the receptor in mediating the actions of GH; thus, it should provide new insight into disorders of growth which are not readily attributable to deficiencies of GH or GH binding sites.