Watson G H, Muldoon T G
Endocrinology. 1985 Oct;117(4):1341-9. doi: 10.1210/endo-117-4-1341.
Rat uterine and anterior pituitary microsomes each contain a population of specific estrogen-binding sites. Saturation binding of estradiol is demonstrable, with an affinity similar to that of the cytosol estrogen receptor (Ka = 1-2 X 10(10) M-1). Dissociation rate kinetic determinations, however, revealed that estrogen-microsomal complexes are 4 times as stable as cytosol estrogen-receptor complexes. Sedimentation properties in sucrose gradients were salt-dependent, yielding values of 10S in KCl-free buffer and 5.5S in the presence of 0.4 M KCl. The concentration of microsomal sites varies in proportion to the level of cytosol estrogen receptor, such that microsomal binding constitutes a consistent 20% of the total extranuclear binding capacity. Binding is sensitive to pronase, but not to ribonuclease or deoxyribonuclease; steroidal specificity differs from cytosol receptor only with respect to a greater extent of competition by progesterone. Microsomal binding sites are readily extractable with KCl-free hypotonic buffer or with 0.4 M KCl, but are resistant to extraction by 0.15 M KCl. The presence of estradiol lends stability to the microsomal binding sites, while high salt has a deleterious effect on their longevity. After exhaustive extraction of binding sites, microsomes are capable of accepting cytosol estradiol-receptor complexes to a level corresponding to the concentration of depleted binding sites; microsomes from nontarget tissue do not manifest such capability. However, the original microsomal estrogen-binding sites are not simply cytosol receptor contaminants, as evidenced by the observations that the microsomal binding site concentration is independent of the volume of tissue homogenate (indicating that a trapping phenomenon is not operative) and that nonextracted microsomes are not potential acceptor sites for cytosol estradiol-receptor complexes. In considering total cellular dynamics of estrogen and estrogen receptor turnover, it thus becomes important to explore the role of the microsomal compartment, since it functions as a repository of specific estrogen-binding sites and may have significant acceptor capability for the cytosol estrogen-receptor complex.
大鼠子宫和垂体前叶微粒体均含有一群特异性雌激素结合位点。可证明雌二醇的饱和结合，其亲和力与胞质雌激素受体相似（Ka = 1 - 2×10¹⁰ M⁻¹）。然而，解离速率动力学测定表明，雌激素 - 微粒体复合物的稳定性是胞质雌激素 - 受体复合物的4倍。蔗糖梯度中的沉降特性取决于盐浓度，在无KCl缓冲液中沉降值为10S，在0.4 M KCl存在下为5.5S。微粒体结合位点的浓度与胞质雌激素受体水平成比例变化，使得微粒体结合占总核外结合能力的20%。结合对链霉蛋白酶敏感，但对核糖核酸酶或脱氧核糖核酸酶不敏感；甾体特异性与胞质受体不同，仅在于孕酮的竞争程度更大。微粒体结合位点可用无KCl的低渗缓冲液或0.4 M KCl轻易提取，但对0.15 M KCl的提取有抗性。雌二醇的存在使微粒体结合位点具有稳定性，而高盐对其寿命有有害影响。在结合位点被彻底提取后，微粒体能够接受胞质雌二醇 - 受体复合物至与耗尽的结合位点浓度相对应的水平；来自非靶组织的微粒体不表现出这种能力。然而，最初的微粒体雌激素结合位点并非简单的胞质受体污染物，这可通过以下观察结果证明：微粒体结合位点浓度与组织匀浆体积无关（表明不存在捕获现象），且未提取的微粒体不是胞质雌二醇 - 受体复合物的潜在接受位点。因此，在考虑雌激素和雌激素受体周转的总细胞动力学时，探索微粒体区室的作用变得很重要，因为它作为特异性雌激素结合位点的储存库，可能对胞质雌激素 - 受体复合物具有重要的接受能力。
