Maitra U S, Khan M S, Zhang X H, Rosner W
Department of Medicine, St. Luke's/Roosevelt Hospital Center, Columbia University College of Physicians and Surgeons, New York, New York 10019.
Endocrinology. 1990 Jul;127(1):278-84. doi: 10.1210/endo-127-1-278.
This investigation was undertaken to ascertain whether rat liver cells contained a receptor for corticosteroid-binding globulin (CBG) that could be differentiated clearly from the asialoglycoprotein receptor. To do this, [125I]CBG, [125I] asialo-CBG, and [125I]asialofetuin were used as probes to differentiate the binding activities of the two receptors. On hepatic membranes, CBG bound to a single set of sites with a Kd of 0.74 microM, asialofetuin bound to a single set of sites with a Kd of 0.018 microM, asialo-CBG bound to two sets of sites with Kd values of 0.004 and 1.4 microM and in the presence of 1 microM asialofetium, asialo-CBG bound to a single set of sites with a Kd of 0.53 microM, not different (P greater than 0.2) from the Kd of CBG. Cross-competition studies using the three 125I-labeled ligands and allowing each to compete with the three radioinert ligands indicated the existence of two separate receptors. Desialylation of hepatic membranes differentially affected the binding of CBG and asialofetuin. Finally, whole cells bound CBG specifically, but internalized it to only a minimal extent (less than 10%). This observation does not support a role for the CBG-receptor system in the entry of steroids into cells.
进行这项研究是为了确定大鼠肝细胞是否含有一种皮质类固醇结合球蛋白（CBG）受体，该受体能够与去唾液酸糖蛋白受体明确区分开来。为此，使用[125I]CBG、[125I]去唾液酸CBG和[125I]去唾液酸胎球蛋白作为探针来区分这两种受体的结合活性。在肝细胞膜上，CBG与一组位点结合，解离常数（Kd）为0.74微摩尔；去唾液酸胎球蛋白与一组位点结合，Kd为0.018微摩尔；去唾液酸CBG与两组位点结合，Kd值分别为0.004和1.4微摩尔，并且在存在1微摩尔去唾液酸胎球蛋白的情况下，去唾液酸CBG与一组位点结合，Kd为0.53微摩尔，与CBG的Kd无差异（P大于0.2）。使用三种125I标记的配体并让每种配体与三种非放射性配体竞争的交叉竞争研究表明存在两种独立的受体。肝细胞膜的去唾液酸化对CBG和去唾液酸胎球蛋白的结合有不同影响。最后，完整细胞特异性结合CBG，但仅将其内化到最小程度（小于10%）。这一观察结果不支持CBG受体系统在类固醇进入细胞过程中起作用。
