Concentration-dependent binding of chlorpyrifos oxon to acetylcholinesterase.
Concentration-dependent binding of chlorpyrifos oxon to acetylcholinesterase.
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毒死蜱与乙酰胆碱酯酶的浓度依赖性结合。
DOI：
10.1093/toxsci/kfm197
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
Sultatos,LesterG
中科院分区：
文献类型：
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作者：
Sultatos,LesterG
多年来，人们已经知道有机磷杀虫剂由于抑制关键酶乙酰胆碱酯酶而引起人类胆碱能危机。活化的有毒杀虫剂代谢物（称为oxons）与乙酰胆碱酯酶的相互作用已经被广泛研究了几十年。然而，最近的研究表明，某些抗胆碱酯酶有机磷与乙酰胆碱酯酶的相互作用比以前认为的更复杂，因为它们的抑制能力已被注意到作为抑制剂浓度的函数而改变。在本报告中，毒死蜱oxon （O，O-二乙基lo -（3,5,6-三氯-2-吡啶基）磷酸盐）与人重组乙酰胆碱酯酶在对硝基苯乙酸存在下孵育，以便更好地动力学表征该oxon与酶的相互作用。测定毒死蜱氧氧的解离常数Kd和磷酸化速率常数k2与氧氧和对硝基苯乙酸浓度的关系，发现Kd随氧氧浓度的变化而变化，而k2不随氧氧浓度变化。对硝基苯乙酸浓度的变化没有改变这些相同的动力学参数。毒死蜱的抑制能力，以byki（k2/Kd）测量，也受到浓度依赖性的结合亲和力变化的影响。这些结果表明，毒死蜱与乙酰胆碱酯酶的浓度依赖性相互作用机制与乙酰硫代胆碱的浓度依赖性相互作用机制不同。在后一种情况下，与乙酰胆碱酯酶外周阴离子位点结合的底物已被证明可以通过阻断产物硫胆碱从活性位点的释放来降低酶的活性。对于毒死蜱，3,5,6-三氯-2-吡啶醇的释放速度无关，因为Ser-203发生磷酸化后，活性位点无法与其他oxon分子相互作用。
The organophosphorus insecticides have been known for many years to cause cholinergic crisis in humans as a result of the inhibition of the critical enzyme acetylcholinesterase. The interactions of the activated, toxic insecticide metabolites (termed oxons) with acetylcholinesterase have been studied extensively for decades. However, more recent studies have suggested that the interactions of certain anticholinesterase organophosphates with acetylcholinesterase are more complex than previously thought since their inhibitory capacity has been noted to change as a function of inhibitor concentration. In the present report, chlorpyrifos oxon (O,O-diethylO-(3,5,6-trichloro-2-pyridyl) phosphate) was incubated with human recombinant acetylcholinesterase in the presence ofp-nitrophenyl acetate in order to better characterize kinetically the interactions of this oxon with enzyme. Determination of the dissociation constant,Kd, and the phophorylation rate constant,k2, for chlorpyrifos oxon with a range of oxon andp-nitrophenyl acetate concentrations revealed thatKd, but notk2, changed as a function of oxon concentration. Changes inp-nitrophenyl acetate concentrations did not alter these same kinetic parameters. The inhibitory capacity of chlorpyrifos oxon, as measured byki(k2/Kd), was also affected as a result of the concentration-dependent alterations in binding affinity. These results suggest that the concentration-dependent interactions of chlorpyrifos oxon with acetylcholinesterase resulted from a different mechanism than the concentration-dependent interactions of acetylthiocholine. In the latter case, substrate bound to the peripheral anionic site of acetylcholinesterase has been shown to reduce enzyme activity by blocking the release of the product thiocholine from the active site gorge. With chlorpyrifos oxon, the rate of release of 3,5,6-trichloro-2-pyridinol is irrelevant since the active site is not available to interact with other oxon molecules after phosphorylation of Ser-203 has occurred.