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1.
Insecticide toxicity and synergism by enzyme inhibitors in 18 species of pest insect and natural enemies in crucifer vegetable crops 总被引：1，自引：0，他引：1
The toxicities of three enzyme inhibitors and their synergistic effects on four insecticides were studied by using the dry film method on field populations of 18 species of insects collected in Jianxin and Shanjie, China, from 2003 to 2005. Meanwhile, the inhibitory effects of these enzyme inhibitors on the activities of acetylcholinesterases (AChE), carboxyesterases (CarE) and glutathione-S-transferases (GST), in vivo, were also studied. In general, triphenyl phosphate (TPP) and diethyl maleate (DEM) showed low toxicities to six herbivorous pest insects, four ladybirds and eight parasitoids. Piperonyl butoxide (PB) exhibited low toxicities to the herbivorous pest insects and ladybirds, but high toxicities to the eight parasitoids. The tolerance to the insecticides in 11 pest insects and natural enemies was mainly associated with the tolerance to PB. PB showed the highest synergism on methamidophos, fenvalerate, fipronil and avermectin in nine species of pest insects and natural enemies. In general, TPP and DEM showed significant synergisms to these four insecticides in four parasitoid species. However, in contrast to their effects on the parasitoids, the synergistic effects of TPP and DEM on the four insecticides by TPP and DEM against four pest insects and one ladybird varied depending on the insect species and enzyme inhibitor. Activity of AChE, CarE or GST could be strongly inhibited, in vivo, by PB, TPP or DEM, depending on the insect species and enzyme inhibitors. From the results obtained in this study, mixed-function oxidase (MFO) was thought to play the most critical role in insect tolerances to the tested insecticides in the field. Low competition existed in the evolution of insecticide resistance in the field populations of parasitoids, as compared with herbivorous pest insects and ladybirds. Possible causes of the high synergistic effects of PB on the four classes of insecticides, based on multiattack on the activity of CarE, GST or AChE in the insect species, are also discussed. 相似文献
2.
羧酸酯酶和乙酰胆碱酯酶在褐飞虱对甲胺磷抗性发展中的作用 总被引：4，自引：0，他引：4
室内抗药性筛选表明,褐飞虱对甲胺磷的抗性呈"快-慢-快"的发展趋势:第1到第4代抗性上升缓慢;第5代到第15代迅速上升,其中又呈现2个发展阶段,以第9代为拐点;第15代后抗性上升变慢。羧酸酯酶在抗药性上升中可能起到十分重要的作用,与LD50变化存在很高的相关性,达到极显著水平,相关系数为0.990 6。乙酰胆碱酯酶不敏感性在抗性发展后期变化很大,第8代到第16代间,与LD50变化存在极显著相关性,相关系数为0.970 1。由此可见,羧酸酯酶可能在褐飞虱对甲胺磷抗性的持续发展中起十分重要的作用,而乙酰胆碱酯酶不敏感性在抗性发展的后期阶段可能起到很重要作用。 相似文献
3.
为明确联苯肼酯对二斑叶螨Tetranychus urticae体内解毒酶系的影响,采用叶片浸渍法测定联苯肼酯对二斑叶螨的亚致死质量浓度LC10和LC30,用这2种浓度分别处理二斑叶螨,并测定60 h内二斑叶螨体内谷胱甘肽S-转移酶（glutathione S-transferase,GST）、羧酸酯酶（carboxylesterase,CarE）和多功能氧化酶（multifunctional oxidase,MFO）的比活力,以及米氏常数Km及最大反应速率vmax的变化。结果显示,经LC10和LC30剂量处理二斑叶螨后,其体内CarE、GST和MFO的活性在6~60 h均受到明显诱导。其中,GST和MFO的比活力在12 h最大,分别为对照的1.25倍、1.60倍和1.63倍、1.84倍,CarE的比活力在48 h最大,为对照的1.27倍和1.37倍;与对照组相比,CarE的Km显著减小,vmax显著升高,而GST和MFO的Km显著增大,vmax显著减小。表明3种酶均参与了二斑叶螨对联苯肼酯的解毒代谢,其中CarE与底物的亲和力最大,反应速率最快,其对联苯肼酯的解毒代谢起主导作用。 相似文献
4.
He Lin Xue Chuan-hua Wang Jin-jun Li Ming Lu Wen-cai Zhao Zhi-mo 《Pesticide biochemistry and physiology》2009,93(1):47-52
A Tetranychus cinnabarinus strain was collected from Chongqing, China. After 42 generations of selection with abamectin and 20 generations of selection with fenpropathrin in the laboratory, this T. cinnabarinus strain developed 8.7- and 28.7-fold resistance, respectively. Resistance to abamectin in AbR (abamectin resistant strain) and to fenpropathrin in FeR (fenpropathrin resistant strain) was partially suppressed by piperonyl butoxide (PBO), diethyl maleate (DEM) and triphenyl phosphate (TPP), inhibitors of mixed function oxidase (MFO), glutathione S-transferases (GST), and hydrolases, respectively, suggesting that these three enzyme families are important in conferring abamectin and fenpropathrin resistance in T. cinnabarinus. The major resistant mechanism to abamectin was the increasing activities of carboxylesterases (CarE), glutathione-S-transferase (GST) and mixed function oxidase (MFO), and the activity in resistant strain developed 2.7-, 3.4- and 1.4-fold contrasted to that in susceptible strain, respectively. The activity of glutathione-S-transferase (GST) in the FeR strain developed 2.8-fold when compared with the susceptible strain, which meant the resistance to fenpropathrin was related with the activity increase of glutathione-S-transferase (GST) in T. cinnabarinus. The result of the kinetic mensuration of carboxylesterases (CarE) showed that the structure of CarE in the AbR has been changed. 相似文献
5.
以田间菜蚜茧蜂为试虫,采用药膜法研究了增效剂胡椒基丁醚(PB)、磷酸三苯酯(TPP)和马来酸二乙酯(DEM)对6种杀虫剂的增效作用。结果表明,三种增效剂对6种杀虫剂均有显著增效作用,其大小依次为PB>DEM>TPP。PB对甲胺磷、阿维菌素、氟虫腈、氰戊菊酯、氯氰菊酯和吡虫啉的增效比达5.0～9.6倍。TPP和DEM对甲胺磷、DEM对氟虫腈的增效比达2.6～3.0倍,但TPP和DEM对阿维菌素、氰戊菊酯和氯氰菊酯、TPP对氟虫腈的增效比均在1.9倍以下。PB、TPP和DEM对吡虫啉的增效比分别高达9.6、6.8和8.2倍。体内抑制试验结果显示,PB、TPP和DEM对菜蚜茧蜂AChE活性无明显抑制作用,而PB和TPP对羧酸酯酶(CarE)、DEM对谷胱甘肽S转移酶(CST)活性有显著抑制作用。由此认为,菜蚜茧蜂对所用的6种杀虫剂的耐药性与多功能氧化酶(MFO)、CarE和GST的解毒作用有关。 相似文献
6.
Hussein M. Ali Hany A. Sharaf Eldeen Mohamed S. Hikal 《Pesticide biochemistry and physiology》2005,83(1):58-65
The inhibitory effects of a recently introduced series of the titled compounds on insect and mammalian acetylcholinesterase (AChE) activity were examined, where the median inhibition concentration (I50) and the inhibition kinetic parameters, bimolecular inhibition rate constant (ki), affinity constant (Ka), and phosphorylation rate constant (kp), were determined for each compound. Results indicated that all examined dioxaphospholenes had less inhibitory effects on mammalian AChE than fenitrothion, a commercial pesticide with moderate mammalian toxicity. The highest selectivity was obtained with compounds containing glutamic and leucine moieties (2.70 and 2.18, respectively) while selectivity of fenitrothion was 0.93. The low inhibitory effects of the examined dioxaphospholenes on mammalian AChE were attributed to their low phosphorylation rates (kp < 2.2 min−1) compared to that of fenitrothion (kp = 4.84 min−1). QSAR equations indicated that the inhibition process is controlled mainly by both the phosphorylation rate (direct effect) and the affinity of compounds toward the enzyme (inverse effect). Although the compounds’ hydrophobicity had no effects on the inhibition process, it affects the compounds’ toxicity since it affects the ability of compounds to penetrate insects to reach the enzyme active site. 相似文献
7.
杀虫增效剂--酶抑制剂对蝶蛹金小蜂和颈双缘姬蜂的影响 总被引：2，自引：0，他引：2
采用药膜法测定了3种酶抑制剂对蝶蛹金小蜂和颈双缘姬蜂杀虫剂敏感性的影响。结果表明，胡椒基丁醚、磷酸三苯酯和马来酸二乙酯显著增大了蝶蛹金小蜂和颈双缘姬蜂对甲胺磷、氰戊菊酯、氯氰菊酯、氟虫腈和阿维菌素的敏感性，胡椒基丁醚的作用显著高于后两者，而后两者之间较为接近。2种寄生蜂对氰戊菊酯和氯氰菊酯的击倒作用具明显的恢复能力，而胡椒基丁醚、磷酸三苯酯和马来酸二乙酯可显著抑制这种击倒恢复能力。上述结果表明，2种寄生蜂对所测试杀虫剂的耐药性与多功能氧化酶、羧酸酯酶和谷胱甘肽-S-转移酶的解毒作用有关，其中多功能氧化酶的作用可能是最重要的。 相似文献
8.
Many organophosphorus (OP) compounds are of the thiono form and in insects or animals are converted by microsomal mixed function oxidases (MFO) into the oxon forms which inhibit acetylcholinesterase (AChE) and give toxic activity. However, certain S-alkyl phosphorothiolates (RS-P(O) <) such as methamidophos, profenophos and prothiophos oxon are strongly insecticidal, but very poor inhibitors of AChE in vitro. Their oxons are converted further to the S-oxides, which either inhibit AChE or decompose, depending on the alkyl substituents on the sulfur atom. It is also inferred in the case of prothiophos oxon that its S-oxide not only inhibits AChE but also conjugates with glutathione (GSH) by the action of glutathione S-transferase (GST), and the conjugate inhibits AChE. Certain phosphoramidates (R2N-P(O) <) such as isofenphos oxon, schradan and propetamphos oxon are weak AChE inhibitors, but strongly insecticidal. It is well known that isofenphos oxon is converted into the stable N-desalkyl form (H2N-P(O) <) by oxidative dealkylation to inhibit AChE. The authors have studied activation of phosphoramidates using 2,4-dichlorophenyl methyl N-alkylphosphoramidates as model compounds using various approaches including computational chemistry, and these studies indicated that the O-aminophosphate structure (R2N-O-P(O) <) is an activated form. 相似文献
9.
Decreased acetylcholinesterase (AChE) sensitivity and metabolic detoxification mediated by glutathione S-transferases (GSTs) were examined for their involvement in resistance to acephate in the diamondback moth, Plutella xylostella. The resistant strain showed 47.5-fold higher acephate resistance than the susceptible strain had. However, the resistant strain was only 2.3-fold more resistant to prothiofos than the susceptible strain. The resistant strain included insects having the A298S and G324A mutations in AChE1, which are reportedly involved in prothiofos resistance in P. xylostella, showing reduced AChE sensitivity to inhibition by methamidophos, suggesting that decreased AChE1 sensitivity is one factor conferring acephate resistance. However, allele frequencies at both mutation sites in the resistant strain were low (only 26%). These results suggest that other factors such as GSTs are involved in acephate resistance. Expression of GST genes available in P. xylostella to date was examined using the resistant and susceptible strains, revealing no significant correlation between the expression and resistance levels. 相似文献
10.
为研究寄主对苹果黄蚜药剂敏感性及体内酶活力的影响,采用生物测定和生化方法分别对取食杏树、李子树、梨树和苹果树的苹果黄蚜种群的药剂敏感性及解毒酶活性进行了测定。供试药剂对杏树、李子树、梨树和苹果树上蚜虫种群的相对毒力指数测定结果表明,吡虫啉为3.53、3.12、2.55和1.00,马拉硫磷为2.42、2.06、1.69和1.00,溴氰菊酯为2.96、1.66、1.43和1.00,灭多威为2.11、1.65、1.37和1.00;对四种药剂的敏感性大小均为杏树种群>李子树种群>梨树种群>苹果树种群。蚜虫的谷胱甘肽-S-转移酶(GST)、乙酰胆碱酯酶(AChE)、羧酸酯酶(CarE)、多功能氧化酶(MFO)的离体酶活力顺序均为苹果种群>梨树种群>李子树种群>杏树种群,四个蚜虫种群的GST活力比值分别为2.32、1.73、1.35和1.00,AChE活力比值为2.48、1.73、1.66和1.00,CarE活力比值为1.60、1.27、1.23和1.00,MFO活力比值为2.02、1.31、1.13和1.00。各种群间的四种酶活力差异均达显著水平。说明寄主植物能影响苹果黄蚜药剂敏感性及解毒酶活力水平。 相似文献
11.
Su50[N'-硝基-1-异丙基-2-(4-硝基苯亚甲基)氨基胍]和Su56(N'-硝基-1-烯丙基-2-正丙基氨基胍)是利用活性亚结构拼接原理合成的具有新烟碱类和缩氨基脲类杀虫剂共同结构特征的硝基缩氨基胍类化合物。为了解Su50和Su56对蚜虫的生物活性及作用机理,采用叶片浸渍法测定了其对多种蚜虫的杀虫活性,用棉叶涂抹药液后接入棉蚜Aphis gossypii Glover测定了其对棉蚜的拒食活性,并采用生化方法测定了不同亚致死浓度(LC_(10)、LC_(25))Su56对棉蚜羧酸酯酶(CarE)、乙酰胆碱酯酶(AChE)、谷胱甘肽S-转移酶(GSTs)和多功能氧化酶(MFO)的酶活性的影响。结果表明:Su50和Su56对棉蚜A.gossypii/桃蚜Myzus persicae Sulzer,苹果黄蚜Aphis citricola van der Goot和梅大尾蚜Hyalopterus amygdali Blanchard均具有一定的杀虫活性,但毒力差异不显著,其中Su50对棉蚜、桃蚜、梅大尾蚜和苹果黄蚜的LC_(50)值分别为13.0、24.2、62.6和14.3mg/L,Su56的LC_(50)值则分别为30.3、30.2、101和3.23 mg/L;同时Su50和Su56对供试棉蚜均具有一定的拒食活性。生化试验结果表明,Su56在LC_(10)和LC_(25)浓度下对棉蚜的CarE、GSTs和MFO酶活性无显著影响,但在LC_(10)浓度下对棉蚜的ACNE酶活性却有显著抑制作用。 相似文献
12.
13.
对甲胺磷敏感性的田间监测结果显示,绒茧蜂存在着抗性演化,毒力生物测定结果与AChE的K_i值的监测结果呈明显的相关性,每年9月至次年2月期间AChE敏感性最低,8月期间敏感性最高。甲胺磷可显著地抑制绒茧蜂AChE、CarE和GSTs的活性。PB和TPP对AChE的活体抑制率极低,但PB可强烈抑制CarE的活性,而TPP仅在高浓度时对CarE有较显著的抑制作用,PB对甲胺磷有显著的增效作用,而TPP对甲胺磷无增效作用。AChE的K_m、V_(max)及K_i值研究结果表明,田间绒茧蜂对有机磷和氨基甲酸酯的抗性与AChE对杀虫剂的不敏感性有关。由此认为,绒茧蜂对有机磷的抗性主要与其最重要的靶标酶AChE的敏感性改变及多功能氧化酶有关。 相似文献
14.
Amino acid substitutions conferring insecticide insensitivity in Ace-paralogous acetylcholinesterase
Y. Kono 《Pesticide biochemistry and physiology》2006,85(3):123-132
Since insecticide insensitivity of acetylcholinesterase (AChE) was, found about 40 years ago, a cause of the resistance to organophosphates in the spider mite, more than 30 insect and Acarus species have added to the instance. Based on the 3-dimensional analysis of Torpedo AChE structure and sequencing of Drosophila AChE gene (Ace), amino acid substitutions conferring the insensitivity have been found in Drosophila melanogaster. However, no amino acid substitution responsible for the AChE insensitivity had been found in insects and Acari except Brachicera flies until the second type of AChE paralogous to Ace was discovered in Schizaphis graminus and Anopheles gambiae. Sequencing of Ace-paralogous AChE cDNAs has been followed in insect species of various orders. Now, various amino acid substitutions are found and correspond to different biochemical properties of insensitive AChEs in relation to the function of substituted amino acids in the 3-dimensional structure. Existence of two AChE genes raises questions about differentiation of the two genes, site of gene expression, and function of each enzyme. 相似文献
15.
小菜蛾对杀虫双的抗性遗传研究 总被引：14，自引：1，他引：13
利用室内选育的敏感品系和抗杀虫双品系为亲本,采用剂量对数—死亡机率值回归线(LD-P线)分析法,研究了小菜蛾对杀虫双的抗性遗传方式。结果表明,小菜蛾对杀虫双的抗性为多基因、常染色体遗传,正、反交F_1的显性度(D)值分别为0.39、0.28,即其主效基因为不完全显性。小菜蛾对杀虫双的抗性现实遗传力较低,h~2=0.052,产生抗性的速率较慢,室内选育119代,抗性仅达122.8倍。抗杀虫双品系和遗传杂交后代(F_1、F_2、BC)对拟除虫菊酯类、氨基甲酸酯类、有机磷类的代表杀虫剂溴氰菊酯、灭多威、敌敌畏等的交互抗性测定结果表明,它们对3种杀虫剂无交互抗性;亲本和杂交后代的多功能氧化酶环氧化活性与杀虫双的抗性水平呈正相关性;乙酰胆碱酯酶活性要比敏感品系低;羧酸酯酶活性与敏感品系无明显差异。 相似文献
16.
Maoxin Zhang Tingting Fang Guilin Pu Xiaoqin Sun Xuguo Zhou Qingnian Cai 《Pesticide biochemistry and physiology》2013
Plant secondary compounds have been documented to be deleterious to insects and other herbivores in diverse ways. In this study, the effect of catechol (phenolics), gramine (alkaloid) and L-ornithine-HCI (non-protein amino acid) on the activities of xenobiotic metabolizing enzymes in English grain aphid, Sitobion avenae, was evaluated. Phase I enzymes investigated in this study included carboxylesterase (CarE), and oxidoreductase, whereas Phase II enzymes were represented by glutathione S-transferase (GST). In general, CarE and GST activities in S. avenae were positively correlated with the concentration of plant secondary compounds in artificial diets. Oxidoreductase activity, however, displayed a different profile. Specifically, peroxidase (POD) and polyphenol oxidase (PPO) activities in S. avenae were positively correlated with concentrations of dietary catechol and gramine, respectively, whereas catalase (CAT) activity was significantly suppressed by the higher concentration of catechol, gramine and L-ornithine-HCl. These combined results suggest that CarE and GST in S. avenae are key enzymes to breakdown a broad spectrum of plant secondary compounds, whereas oxidoreductase, including PPO and POD, degrades specific groups of plant secondary compounds. 相似文献
17.
The oriental tobacco worm, Helicoverpa assulta Guenée, is one of the most destructive pests of tobacco and peppers in China. We determined the susceptibility of H. assulta reared on an artificial diet, chili pepper and tobacco to four insecticides (fenvalerate, phoxim, methomyl, indoxacarb) under laboratory conditions associated with the activities of acetylcholinesterase (AChE), carboxylesterase (CarE) and glutathione S-transferase (GST) in its larvae. H. assulta larvae that were fed with chili pepper were more susceptible to fenvalerate, indoxacarb, and phoxim than those that were fed with tobacco and the artificial diet, but not to methomyl. The larvae that were fed with chili pepper were 3.65-, 2.49-, 1.92- and 2.44-fold more susceptible to fenvalerate, phoxim, methomyl, and indoxacarb than those fed with tobacco, respectively. The AChE activities of H. assulta larvae that were fed with chili pepper and tobacco were 2.12 and 1.07 μmol mg−1 15 min−1, respectively, almost 2-fold difference. The CarE activity of H. assulta larvae that were fed with chili pepper, tobacco and the artificial diet was 4.12, 7.40 and 7.12 μmol mg−1 30 min−1, respectively. Similarly, the GST activities of H. assulta larvae that were fed with chili pepper, tobacco and the artificial diet was 52.02, 79.37 and 80.02 μmol mg−1 min−1, respectively. H. assulta larvae that were fed with chili pepper were more resistance to the tested insecticides. The low activities of AChE and the high activities of CarE and GST lead to H. assulta become more susceptible to the tested insecticides. 相似文献
18.
Methamidophos (O,S-dimethylphosphoramidothioate, Monitor) is an organophosphorus, cholinesterase-inhibiting insecticide. The rate constant (ki) for inhibiting rat plasma cholinesterase (ChE) was 1.57 ± 0.03 × 103M?1 min?1, for rat erythrocyte ChE was 8.86 ± 1.10 × 103M?1 min?1, and for rat brain ChE was 6.58 ± 0.42 M?1 min?1. Brain and plasma cholinesterases spontaneously recovered from over 90% inhibition at 30 min to 50% inhibition in 4 and 14 hr, respectively. Pralidoxime increased the rate of reactivation in vitro. In vivo, rats poisoned with methamidophos exhibited signs of cholinergic stimulation. The LD50 of ip methamidophos in male rats was 15 ± 0.7 mg/kg. Pralidoxime (60 mg/kg) and atropine (10 mg/kg) given with the methamidophos increased the LD50 to 52 ± 4.9 mg/kg and 60 ± 0.4 mg/kg, respectively. In rats given 12.5 mg methamidophos (an LD20), ChE activity was depressed 95 ± 12.5% in plasma, 92 ± 0.6% in stomach, and 88 ± 1% in brain at 1 hr after injection. At 48 hr after injection ChE activity had returned to 60% or more of control values in each of the tissues. Administration of a single dose of 60 mg/kg of pralidoxime along with methamidophos did not increase ChE activities at the times and places it was measured. 相似文献
19.
The tissue distribution and excretion of [14CH3S]methamidophos was followed in female Sprague-Dawley rats after intravenous injection at a toxic, but nonlethal, dose (8 mg/kg). Radiolabel was rapidly distributed to all tissues at approximately equal concentrations. Peak tissue levels were achieved within 1–10 min except in the central and peripheral nervous system where peak levels (40 nmol/g) were found between 20 and 60 min, corresponding to peak signs of toxicity. Within 24 hr of dosing, 47% of the radioactivity was recovered in the urine and 34% as 14CO2 with <5% in the feces over 7 days. Cholinesterase (ChE) inhibition was measured in erythrocytes, plasma, and various regions of the central nervous system (CNS) at selected times after administration of methamidophos at 8 mg/kg. The degree of acetylcholinesterase (AChE) inhibition in the three CNS regions was similar, reaching a minimum of 15–20% of control values at 30–60 min, when toxicity was most severe. The degree of erythrocyte AChE inhibition was less than that of the CNS although the time course was similar. Plasma ChE inhibition was more rapid than that of the CNS or erythrocytes and reactivation was slower. When similar concentrations of methamidophos to those found in vivo were incubated with CNS homogenates, plasma, or erythrocytes in vitro (5 × 10?5M) a similar degree of inhibition occurred over the same time course. It is, therefore, concluded that the cholinergic toxicity produced by methamidophos is a result of the in vivo stability of this compound combined with its entry into the nervous system in sufficiently high concentrations to inhibit AChE. 相似文献
20.
《Pesticide biochemistry and physiology》1987,28(2):224-238
At 37°C and pH 7.4–8.0, five higher O-alkyl analogs of methamidophos and four O-alkyl O-2,5-dichlorophenyl phosphoramidates all were more potent progressive inhibitors of hen brain AChE and neuropathy target esterase (NTE) than was methamidophos itself. For AChE, ka increased from 7.2 × 102 to 1.0 × 105 M−1 min−1 between methyl and n-hexyl S-methyl esters and from 9.3 × 103 to 8.9 × 105 M−1 min−1 between ethyl and n-hexyl dichlorophenyl analogs. For NTE, the ranges were from 16 to 7.9 × 104 for S-methyl esters, and were 9.7 × 104 to 7.8 × 106 M−1 min−1 for dichlorophenyl. S-methyl esters were more active against AChE than against NTE and all the dichlorophenyl esters were more active against NTE than against AChE. Spontaneous reactivation of 75–100% activity without aging of AChE was found after 19 hr incubation at 37°C after inhibition by all nine straight-chain alkyl analogs. After inhibition by O-isopropyl S-methyl phosphorothioamidate, some spontaneous reactivation with complete aging of all remaining inhibited AChE occurred during 19 hr. No spontaneous reactivation or aging of inhibited NTE was detected. It was concluded that the molecular structures of the inhibited enzymes obtained from equivalent compounds in the two series of inhibitors were identical and that the leaving groups were, therefore, S-methyl and O-2,5-dichlorophenyl, respectively. Although hen brain NTE inhibited by methamidophos in vitro did not age, cases of delayed neuropathy in man have been reported and, presumably, require aging as well as inhibition of NTE. Possible explanations of this apparent discrepancy include (i) the fact that methamidophos consists of two chiral forms and that the form seen to be active in vitro may be disposed of preferentially in vivo, (ii) the possibility of activation in vivo to a different inhibitor, (iii) differences between conformation and ease of aging of inhibited NTE in vitro and in vivo, and (iv) species differences. 相似文献