Buckley D I, Ramachandran J
Proc Natl Acad Sci U S A. 1981 Dec;78(12):7431-5. doi: 10.1073/pnas.78.12.7431.
The binding of corticotropin (ACTH) to receptors on isolated rat adrenocortical cells was investigated with the aid of [[125I]ITyr23, Phe2, Nle4]ACTH-(1-38) (125I-ACTH analog) which retained full biological potency and had a specific radioactivity of 1800 +/- 75 Ci/mmol. Binding was highly specific to adrenocortical cells, and the radioactive peptide was displaced by low concentrations of ACTH but not by other basic peptides. Binding was rapid, reversible, and linearly related to the number of cells. 125I-ACTH analog was not significantly degraded by incubation with the cells at 23 degrees C for 1 hr. Scatchard analysis of the binding was compatible with a single class of binding sites with Kd = 1.41 +/- 0.21 nM, and the number of sites was estimated to be 3840 +/- 1045 per cell. The binding curve was superimposable on the concentration-response curve for cyclic AMP. Small, but significant amounts of 125I-ACTH analog were bound at concentrations sufficient for maximal stimulation of steroidogenesis. For a series of ACTH analogs, the concentrations of the peptides required for half-maximal stimulation of cyclic AMP production were in excellent agreement with the concentration required for half-maximal inhibition of binding. These results suggest that the adrenocortical cells contain only one class of ACTH receptors and that stimulation of a small fraction of these receptors (less than 3%) is sufficient for maximal steroidogenesis.
借助[125I]ITyr23、Phe2、Nle4]促肾上腺皮质激素-(1 - 38)(125I - 促肾上腺皮质激素类似物)研究了促肾上腺皮质激素(ACTH)与分离的大鼠肾上腺皮质细胞上受体的结合情况，该类似物保留了全部生物活性，比放射性为1800±75 Ci/mmol。结合对肾上腺皮质细胞具有高度特异性，放射性肽可被低浓度的ACTH取代，但不能被其他碱性肽取代。结合迅速、可逆，且与细胞数量呈线性相关。在23℃下与细胞孵育1小时，125I - 促肾上腺皮质激素类似物未被显著降解。对结合进行Scatchard分析，结果符合一类结合位点，Kd = 1.41±0.21 nM，每个细胞的结合位点数估计为3840±1045个。结合曲线与环磷酸腺苷的浓度 - 反应曲线重叠。在足以最大程度刺激类固醇生成的浓度下，有少量但显著量的125I - 促肾上腺皮质激素类似物被结合。对于一系列促肾上腺皮质激素类似物，使环磷酸腺苷产生量达到半数最大刺激所需的肽浓度与使结合抑制达到半数最大所需的浓度非常一致。这些结果表明，肾上腺皮质细胞仅含有一类ACTH受体，并且刺激这些受体的一小部分(小于3%)就足以实现最大程度的类固醇生成。
