Kubokawa K, Ishii S
Department of Biology, School of Education, Waseda University, Tokyo, Japan.
Gen Comp Endocrinol. 1987 Nov;68(2):260-70. doi: 10.1016/0016-6480(87)90037-2.
We demonstrate that highly purified bullfrog (f) follicle-stimulating hormone (FSH) and luteinizing hormone (LH) bind specifically and significantly to a crude plasma membrane fraction of bullfrog liver. The other extragonadal organs of the bullfrog showed little or no specific binding. Specific bindings of 125I-fFSH and 125I-fLH to plasma membranes are saturable processes, and are time-, pH-, and temperature-dependent. Scatchard plots of fFSH and fLH were linear. The association constant of equilibrium (Ka) of the specific fFSH binding sites was 4.77 +/- 1.24 X 10(9)M-1 (mean +/- SEM) and the number of sites was 0.262 +/- 0.042 fmol/mg protein (mean +/- SEM). The Ka of the specific fLH binding sites was 5.38 +/- 1.27 X 10(9)M-1 (mean +/- SEM) and the number was 0.315 +/- 0.019 fmol/mg protein (mean +/- SEM). Competition experiments revealed that both fFSH and fLH use the same single class of binding sites. Binding of rat, chicken, bullfrog, and salmon gonadotropins to plasma membranes of the testis and liver of various vertebrates was studied. A significant degree of specific binding was detected only in combinations of bullfrog gonadotropins and amphibian livers. The concentration of adenosine 3'-5'-monophosphate (cAMP) in mince or primary culture cells of bullfrog liver was greatly increased by adding fFSH and fLH to the medium. Bullfrog LH was more potent than fFSH in increasing cAMP concentration, although they were not distinguished by specific binding sites. These data suggest that not only the gonads but also the liver is the target of gonadotropins in the bullfrog, although the final hepatic function controlled by gonadotropins remains unknown.
我们证明，高度纯化的牛蛙卵泡刺激素（FSH）和促黄体生成素（LH）能特异性且显著地与牛蛙肝脏的粗质膜部分结合。牛蛙的其他性腺外器官显示出很少或没有特异性结合。125I标记的牛蛙FSH（125I-fFSH）和125I标记的牛蛙LH（125I-fLH）与质膜的特异性结合是可饱和过程，并且与时间、pH值和温度有关。fFSH和fLH的Scatchard图呈线性。特异性fFSH结合位点的平衡缔合常数（Ka）为4.77±1.24×10⁹M⁻¹（平均值±标准误），结合位点数为0.262±0.042 fmol/mg蛋白质（平均值±标准误）。特异性fLH结合位点的Ka为5.38±1.27×10⁹M⁻¹（平均值±标准误），结合位点数为0.315±0.019 fmol/mg蛋白质（平均值±标准误）。竞争实验表明，fFSH和fLH都使用同一类单一结合位点。研究了大鼠、鸡、牛蛙和鲑鱼促性腺激素与各种脊椎动物睾丸和肝脏质膜的结合情况。仅在牛蛙促性腺激素与两栖类肝脏的组合中检测到显著程度的特异性结合。向培养基中添加fFSH和fLH可使牛蛙肝脏切碎组织或原代培养细胞中的3',5'-环磷酸腺苷（cAMP）浓度大幅增加。尽管fFSH和fLH在特异性结合位点上没有区别，但牛蛙LH在增加cAMP浓度方面比fFSH更有效。这些数据表明，在牛蛙中，不仅性腺，而且肝脏也是促性腺激素的作用靶点，尽管促性腺激素所控制的最终肝脏功能尚不清楚。
