Singer C J, Khan M S, Rosner W
Department of Medicine, St. Luke's-Roosevelt Hospital Center, New York, New York.
Endocrinology. 1988 Jan;122(1):89-96. doi: 10.1210/endo-122-1-89.
Specific binding sites for corticosteroid-binding globulin (CBG) were detected on membranes prepared from rat spleen. The binding sites are typical of membrane receptors; they are saturable, specific, have high affinity, and require Mg2+ or Ca2+ for binding. There was little specific binding at 4 C, and maximal binding was obtained at 37 C. Scatchard analysis revealed a single set of binding sites with an apparent Kd of 0.84 microM, and a binding capacity of 39 pmol/mg membrane protein. The sites were specific for CBG; binding of [125I]CBG was not inhibited by a 10,000-fold excess of either rat albumin or rat transferrin. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate of the membrane-bound [125I]CBG revealed the presence of lower mol wt iodinated products which were undetectable in the unbound [125I]CBG fraction. Further, whereas the electrophoretic patterns from uterine, pulmonary, and renal membranes showed that the less mobile band (mol wt, 60K) of the normal CBG doublet appeared to be metabolized to a greater extent than the more mobile band (mol wt, 52K), those from splenic membranes showed equal metabolism of both parts of the doublet.
在从大鼠脾脏制备的膜上检测到了皮质类固醇结合球蛋白（CBG）的特异性结合位点。这些结合位点具有膜受体的典型特征；它们具有饱和性、特异性、高亲和力，且结合需要Mg2+或Ca2+。在4℃时特异性结合很少，在37℃时获得最大结合。Scatchard分析显示有一组单一的结合位点，其表观解离常数（Kd）为0.84微摩尔，结合容量为39皮摩尔/毫克膜蛋白。这些位点对CBG具有特异性；[125I]CBG的结合不会被过量10000倍的大鼠白蛋白或大鼠转铁蛋白所抑制。在十二烷基硫酸钠存在下对膜结合的[125I]CBG进行聚丙烯酰胺凝胶电泳，结果显示存在较低分子量的碘化产物，这些产物在未结合的[125I]CBG组分中无法检测到。此外，子宫、肺和肾膜的电泳图谱显示，正常CBG双峰中迁移较慢的条带（分子量60K）似乎比迁移较快的条带（分子量52K）代谢程度更高，而脾脏膜的电泳图谱显示双峰的两个部分代谢程度相同。
