Yamaguchi T, Saisu H, Mitsui H, Abe T
Department of Neurochemistry, Niigata University, Japan.
J Biol Chem. 1988 Jul 5;263(19):9491-8.
The omega-conotoxin receptor in brain membranes contains components of Mr approximately equal to 310,000, approximately equal to 230,000, and 37,000 as identified by photoaffinity labeling. The toxin specifically bound to two sites with apparent dissociation constants (Kd) of approximately 3 pM and 3.5 nM under the conditions employed. There was about 8 times more of the low affinity site than the high affinity site. Binding was not affected by dihydropyridines or verapamil. However, diltiazem stereospecifically inhibited the binding to the high affinity site. Dissociation of the toxin from the membranes was very slow and only partial. Among the detergents tested, digitonin solubilized the highest toxin-binding activity. The digitonin extract contained only a single class of binding sites with an apparent Kd of about 0.46 nM. Probably only the high affinity binding site was recovered in active form in digitonin extract. The properties of the toxin binding to digitonin extract were in good agreement with those of the binding to the high affinity site in the original membranes. Photoaffinity labeling of the digitonin extract indicated that the solubilized toxin receptor contained the two large components (Mr congruent 310,000 and approximately equal to 230,000) observed in the membranes.
通过光亲和标记鉴定，脑膜中的ω-芋螺毒素受体含有分子量约为310,000、约230,000和37,000的成分。在所采用的条件下，毒素特异性结合到两个位点，其表观解离常数（Kd）分别约为3 pM和3.5 nM。低亲和力位点的数量比高亲和力位点多约8倍。结合不受二氢吡啶或维拉帕米的影响。然而，地尔硫卓立体特异性地抑制与高亲和力位点的结合。毒素从膜上的解离非常缓慢且只是部分解离。在所测试的去污剂中，洋地黄皂苷溶解的毒素结合活性最高。洋地黄皂苷提取物仅含有一类结合位点，其表观Kd约为0.46 nM。可能在洋地黄皂苷提取物中只有高亲和力结合位点以活性形式被回收。毒素与洋地黄皂苷提取物结合的特性与与原始膜中高亲和力位点结合的特性高度一致。洋地黄皂苷提取物的光亲和标记表明，溶解的毒素受体含有在膜中观察到的两种大分子量成分（分子量约为310,000和约230,000）。
