Matsumoto K, Eldefrawi M E, Eldefrawi A T
Department of Pharmacology and Experimental Therapeutics, University of Maryland, School of Medicine, Baltimore 21201.
Toxicol Appl Pharmacol. 1988 Sep 15;95(2):220-9. doi: 10.1016/0041-008x(88)90158-5.
Binding of [35S]t-butylbicyclophosphorothionate ([35S]TBPS) to Torpedo electric organ membranes was characterized. A dose- and pH-dependent binding (100.8 pmol/mg protein) was detected with a single affinity (Kd of 0.9 microM) in the presence of 150 mM KCl at pH 6.8. Other anions such as Br- and I- also increased binding affinity, but to a lower degree than Cl-, which increased the affinity by two- to threefold. In presence of 150 mM KCl, [35S]TBPS binding was inhibited noncompetitively by Zn2+ and by 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS) (IC50 of 9 microM). The gamma-isomer of hexachlorocyclohexane (BHC) was much more potent in inhibiting this [35S]TBPS binding and the inhibition was competitive (Ki = 40 nM). Like binding of [35S]TBPS to the gamma-aminobutyric acid (GABA) receptor, its binding to Torpedo membranes was inhibited by pentobarbital, mephobarbital, and hexobarbital (IC50 of 85, 225, and 300 microM), respectively), but not by phenobarbital. Binding was not inhibited by diazepam, GABA, bicuculline, or avermectin B1a, ligands that bind to the GABAA receptor. [35S]TBPS binding was inhibited by BHC isomers with the following decreasing order of potency alpha = gamma greater than sigma greater than beta, and by cyclodiene insecticides. Endrin was more potent than dieldrin, but endosulfan I and II had similar effects. The data suggest that the binding site for polychlorocycloalkane insecticides on this protein is much less stereoselective than that of the Cl- channel of the GABAA receptor. Also, even though this Torpedo protein has higher affinity for insecticides, such as gamma-BHC, than does the GABAA receptor, it is the latter whose specificity correlates best with polychlorocycloalkane toxicity. Nevertheless, because of its high affinity for gamma-BHC such a protein in muscles or brain may be an important target for the action of this insecticide.
对[35S]叔丁基双环硫代磷酸酯（[35S]TBPS）与电鳐电器官膜的结合特性进行了研究。在pH 6.8、150 mM KCl存在的条件下，检测到其结合呈剂量和pH依赖性（100.8 pmol/mg蛋白质），具有单一亲和力（解离常数Kd为0.9 microM）。其他阴离子如Br-和I-也能增加结合亲和力，但程度低于Cl-，Cl-可使亲和力提高两到三倍。在150 mM KCl存在时，[35S]TBPS的结合受到Zn2+和4,4'-二异硫氰酸-2,2'-二苯乙烯二磺酸（DIDS）的非竞争性抑制（半数抑制浓度IC50为9 microM）。六氯环己烷（BHC）的γ异构体对这种[35S]TBPS结合的抑制作用更强，且抑制作用具有竞争性（抑制常数Ki = 40 nM）。与[35S]TBPS与γ-氨基丁酸（GABA）受体的结合情况类似，其与电鳐膜的结合分别受到戊巴比妥、美索比妥和己巴比妥的抑制（IC50分别为85、225和300 microM），但不受苯巴比妥抑制。地西泮、GABA、荷包牡丹碱或阿维菌素B1a（与GABAA受体结合的配体）对结合无抑制作用。[35S]TBPS的结合受到BHC异构体的抑制，其效力顺序为α = γ＞σ＞β，同时也受到环二烯类杀虫剂的抑制。异狄氏剂比狄氏剂的抑制作用更强，但硫丹I和II的作用相似。数据表明，多氯环烷烃类杀虫剂在该蛋白质上的结合位点比GABAA受体的Cl-通道的立体选择性低得多。此外，尽管这种电鳐蛋白质对γ-BHC等杀虫剂的亲和力高于GABAA受体，但与多氯环烷烃毒性相关性最佳的是后者。然而，由于其对γ-BHC具有高亲和力，肌肉或大脑中的这种蛋白质可能是该杀虫剂作用的重要靶点。
