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1.
A hydrophilic form of acetylcholinesterase (AChE) was purified from N-methyl carbamate susceptible (SA) and highly N-methyl carbamate-resistant (N3D) strains of the green rice leafhopper (GRLH), Nephotettix cincticeps Uhler. Both of purified AChE from SA and N3D strains displayed the highest activities toward acetylthiocholine (ATCh) at pH 8.5. In the SA strain, the optimum concentrations for ATCh, propionylthiocholine (PTCh), and butyrylthiocholine (BTCh) were about 1 × 10−3, 2.5 × 10−3, and 1 × 10−3 M, respectively. However, in the N3D strain, substrate inhibition was not identified for ATCh, PTCh, and BTCh to 1 × 10−2 M. The Km value in the SA strain was 51.1, 39.1, and 41.6 μM and that in the N3D strain was 91.8, 88.1, and 85.2 μM for ATCh, PTCh, and BTCh, respectively. The Km value in the N3D strain indicated about 1.80-, 2.25-, and 2.05-fold lower affinity than that of the SA strain for ATCh, PTCh, and BTCh, respectively. The Vmax value in the SA strain was 70.2, 30.5, and 4.6 U/mg protein and that in the N3D strain was 123.0, 27.0, and 14.5 U/mg protein for ATCh, PTCh, and BTCh, respectively. The Vmax value in the N3D strain was 1.75- and 3.15-fold higher for ATCh and BTCh than that in the N3D strain. However, it was 1.13-fold lower for PTCh. The increased activity of AChE in the N3D strain is due to the qualitatively modified enzyme with a higher catalytic efficiency. The bimolecular rate constant (ki) for propoxur was 27.1 × 104 and 0.51 × 104 M−1 min−1 in the SA and N3D strain and that for monocrotophos was 0.031 × 104 and 2.0 × 104 M−1 min−1 in the SA and N3D strain. AChE from the N3D strain was 53-fold less sensitive than SA strain to inhibition by propoxur. In contrast, AChE from the N3D strain was 65-fold more sensitive to inhibition by monocrotophos than AChE from the SA strain. This indicated negatively correlated cross-insensitivity of AChE to propoxur and monocrotophos.  相似文献   

2.
Glutathione transferase (GST) was purified from the hindgut of grasshopper (Zonocerus variegatus) a polyphagous insect. The purified enzyme had a native molecular weight of 40 kDa and a subunit molecular weight of 19 kDa. The purified enzyme could conjugate glutathione (GSH) with 1-chloro-2,4-dinitrobenzene (CDNB), paranitrobenzylchloride, paranitrophenylacetate, 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBDCl), and 1,2-dichloro-4-nitrobenzene (DCNB) with specific activities of 3.3 ± 0.3, 0.49 ± 0.10, 0.10 ± 0.002, 1.2 ± 0.2, and 1.7 ± 0.4 μmol/min/mg protein, respectively. CDNB appears to be the best substrate with a specificity constant, kcat/Km, of 1.8 ± 0.1 × 10−4 M−1 S−1. The kinetic mechanism of Z. variegatus GST (zvGST) in the conjugation of GSH with some electrophilic substrates appears complex. Conjugation of GSH with DCNB was inhibited by high DCNB concentration, while with NBDCl, as the electrophilic substrates, different values of Km were obtained at high and low concentrations of the substrates. Cibacron blue, hematin, S-hexylglutathione, and oxidized glutathione inhibited the enzyme with I50 values of 0.057 ± 0.004, 0.80 ± 0.2, 33 ± 2 μM, and 5.2 ± 0.3 mM, respectively. The nature of inhibition by each of these inhibitors is either competitive or non-competitive at varying GSH or CDNB as substrates. NADH and NAD+ inhibited the enzyme with an I50 value of 0.4 ± 0.01 and 11 ± 1 mM, respectively. NADH at a concentration of 0.54 mM completely abolished the activity. As part of its adaptation, the flexible kinetic pathway of detoxication by zvGST may assist the organism in coping with various xenobiotics encountered in its preferred food plants.  相似文献   

3.
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   

4.
Anti-vitamin K drugs are widely used as anticoagulant in human thromboembolic diseases. Similar compounds have also been used as rodenticides to control rodent population since 1950s. Massive use of first generation anticoagulants, especially warfarin, has lead to the development of genetic resistances in rodents. Similar resistances have been reported in human. In both cases, polymorphisms in VKORC1 (Vitamin K epoxide reductase subunit 1), the subunit 1 of the VKOR (Vitamin K epoxide reductase) complex, were involved. In rats (Rattus norvegicus), the Y139F mutation confers a high degree of resistance to warfarin. Little is known about the in vitro consequences of Y139F mutation on inhibitory effect of different anticoagulants available. A warfarin-susceptible and a warfarin-resistant Y139F strain of wild rats (Rattus norvegicus) are maintained in enclosures of the Lyon College of Veterinary Medicine (France). Using liver microsomes from susceptible or resistant rats, we studied inhibition parameters by warfarin (Ki = 0.72 ± 0.1 μM; 29 ± 4.1 μM), chlorophacinone (Ki = 0.08 ± 0.01 μM; 1.6 ± 0.1 μM), diphacinone (Ki = 0.07 ± 0.01 μM; 5.0 ± 0.8 μM), coumachlor (Ki = 0.12 ± 0.02 μM; 1.9 ± 0.2 μM), coumatetralyl (Ki = 0.13 ± 0.02 μM; 3.1 ± 0.4 μM), difenacoum (Ki = 0.07 ± 0.01 μM; 0.26 ± 0.02 μM), bromadiolone (Ki = 0.13 ± 0.02 μM; 0.91 ± 0.07 μM), and brodifacoum (Ki = 0.04 ± 0.01 μM; 0.09 ± 0.01 μM) on VKOR activity. Analysis of the results leads us to highlight different anticoagulant structural elements, which influence inhibition parameters in both susceptible and Y139F resistant rats.  相似文献   

5.
Organophosphorus pesticides (OPs) are of environmental significance due to their high toxicity to animals. Binding to plasma proteins may effective influence the toxicological properties of xenobiotics. In an attempt to evaluate the affinity of phenthoate (PTA) to bovine serum albumin (BSA) and inhibitory ability of bound PTA to acetylcholinesterase (AChE), we investigated the interactions between phenthoate (PTA) and bovine serum albumin (BSA) using tryptophan fluorescence quenching and subsequent inhibition on AChE activity by PTA. The results showed that PTA caused the fluorescence quenching of BSA because of the formation of a PTA-BSA complex. Quenching constants (Ksv), determined using the Sterns-Volmer equation to provide a measure of the binding affinity between PTA and BSA at 303, 306, 310 and 313 K were (3.4295 ± 0.0763) × 10−4, (3.2446 ± 0.0635) × 10−4, (3.0434 ± 0.0856) × 10−4 and (2.8262 ± 0.0569) × 10−4 M−1, respectively. The thermodynamic parameters, ΔH and ΔS were −25.04 kJ mol−1 and 168.94 J mol−1 K−1, respectively, which indicated that the electrostatic interactions played a major role in PTA-BSA association. The presence of BSA consistently reduced the inhibitory ability of PTA on AChE, with the relative activity being increased from 46.98 to 61.71% for the concentration range of BSA between 0 and 4.0 g L−1.  相似文献   

6.
The relationship between the physicochemical properties (molar volume, partition coefficient, and dissociation constant) of slow-acting systemic postemergence xenobiotics and their uptake and translocation to the sites of action was investigated using the nonlinear, dynamic simulation model ERMESSE. When the pKa was held constant at 4.0, the model enables the prediction of the uptake of a systemic xenobiotic as a function of its partition coefficient and molar volume. The model also considered the effects of the physicochemical properties of a systemic xenobiotic on its long-distance translocation within the vascular tissues. For instance, when the log Kow and pKa were held constant at 1.5 and 6.0, respectively, the model predicted a higher translocation rate (55%) for molecules with a small (e.g., MV = 100 cm3 mol−1) as opposed to a large (e.g., MV = 300 cm3 mol−1, 33%) molar volume. In addition, the theoretical predictions from the ERMESSE model showed that any xenobiotic with a molar volume not exceeding 300 cm3 mol−1 could provide an uptake ?50% and a translocation rate ?25% when its log Kow is between −0.5 and 2.5 and its pKa is between 0.0 and 8.0.  相似文献   

7.
The in vitro inhibition potency of some organophosphates (OPs) and carbamates (CAs) which are widely used to control plant-parasitic nematodes on acetylcholinesterase (AChE) of Meloidogyne javanica, Heterodera avenae and Tylenchulus semipenetrans, the major pathogens responsible for the damage of a wide range of crops in Al-Qassim region, Saudi Arabia was examined. AChE of H. avenae activity was 1.58- and 1.51-fold greater than that of T. semipenetrans or M. javanica, respectively. The order of inhibition potency of the tested compounds against T. semipenetrans AChE was: carbofuran > paraoxon > oxamyl > fenamiphos > phorate-sulfoxide > aldicarb, where the corresponding concentrations that inhibited 50% of the nematode AChE activity (I50) were 5 × 10−8, 7 × 10−7, 7.5 × 10−7, 2 × 10−6, 2 × 10−4 and 2 × 10−3 M, respectively. Paraoxon, fenamiphos and carbofuran exhibited high inhibition potency against M. javanica AChE where the I50 values were below 1 nM. Phorate-sulfoxide and aldicarb were potent inhibitors of M. javanica AChE with I50 values of 3.8 and 8 nM, respectively, while oxamyl exhibited low inhibition potency with I50 of 15 nM. Fenamiphos and paraoxon showed the highest I50 values of <100 μM against H. avenae followed by oxamyl (I50 < 1 mM), whereas paraoxon, carbofuran and aldicarb showed low potency with I50 values >1 mM. All the tested compounds exhibited high inhibition potency to AChE of M. javanica than T. semipenetrans or H. avenae. Except phorate-sulfoxide in M. javanica the inhibition pattern and implied mechanism for all the tested compounds for the three nematodes is suggested to be a linear mixed type (a combination of competitive and non-completive type).  相似文献   

8.
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   

9.
Amitraz is a pesticide targeting the octopaminergic receptors. In a previous study, octopamine, a biogenic amine, was found to induce a biphasic effect on the honeybee heart, inhibition at low concentrations and excitation at high concentrations. Furthermore, the honeybee heart was found to be far more sensitive to octopamine compared to other insect hearts. The objective of the present study was to investigate the effects of amitraz on the electrical and mechanical properties of the honeybee heart ex vivo and on the heart rate in vivo. In ex vivo conditions, amitraz at 10−12 M caused a significant inhibition in the mechanical (p < 0.05, n = 4) and electrical properties (p < 0.05, n = 4). Higher concentrations such as 10−9 and 10−6 M induced a biphasic effect, with total inhibition for 7.86 ± 1.26 min (n = 7), followed by strong excitation of spontaneously-generated contractions (n = 7). The initial elimination of heart activity was caused by strong hyperpolarization, while the subsequent excitation was caused by a depolarization in the membrane potential of pacemaker cells at 10−9 M (n = 8). In the in vivo experiments, abdominal injection or oral application of 0.20 ng of amitraz per bee induced a persistent increase of 134.28 ± 4.07% (p < 0.05, n = 4) in the frequency of the cardiac action potentials. The above responses clearly show that the heart of the honeybee is extremely vulnerable to amitraz, which is nevertheless still used inside beehives, ostensibly to “protect” the honeybees against their main parasite, Varroa destructor.  相似文献   

10.
The present study was conducted to determine the 96 h-LC50 of benomyl to the Nile tilapia, Oreochromis niloticus and to investigate the biochemical or hematological indices of blood and the alterations in the antioxidant enzymes of this fish in response to sublethal concentrations of benomyl. Fish weighing 71.61 ± 12.05 g were used in this study; they were subjected to fasting for 4 weeks before treatment. An aqueous solution of benomyl (0, 0.5, 1, 2, 4, 8, and 16 mg L−1) was administered for 96 h to determine the LC50. The 96 h-LC50 value of benomyl was 4.39 (3.23-5.60) mg L−1 in the present study. For 5 weeks, the aqueous solution of benomyl (0, 100, 200, and 400 μg L−1) was administered to investigate its effect on the hematological parameters and antioxidant enzymes. The predominant hematological findings in fish exposed to benomyl were as follows: no significant change in the Hb (g dL−1) level, MCV (μm3), MCH (pg) and MCHC (%) as compared to the control. Benomyl exposure led to greater increases in the GPT, GOT (Karmen-unit), LDH (Wroblewski unit), total cholesterol, Fe, and Ca (mg dL−1) values, whereas the levels of ALP (KA unit), total protein, triglyceride, albumin, and Mg (mg dL−1) did not increase. Benomyl increased the in vivo HSI (%), GST (nmol min−1 mg protein−1), and SOD (U mg protein−1) values in the fish livers in the test group, unlike those in the control group for 5 weeks. At concentrations higher than 100 μg L−1, benomyl affected the GST and SOD levels of Nile tilapia in a dose- and time-dependent manner. The present findings suggest that the in vivo hepatotoxicity associated with benomyl may, in part, result from the hematological index, and antioxidants may provide limited protection against benomyl toxicity.  相似文献   

11.
Inhibitory effects of five organophosphorus pesticides (diazinon, malathion, chlorpyrifos, azinphos-methyl and phorate) and their oxo-analogs on human myeloperoxidase (MPO) activity were investigated. While inspecting separately peroxidase and chlorination activity, it was observed that investigated OPs affect peroxidase activity, but not chlorination activity. Among investigated pesticides, malathion and malaoxon have showed the highest power to inhibit MPO peroxidase activity with IC50 values of the order of 3 × 10−7 and 5 × 10−9 M, respectively. It was proposed that inhibition trend is rendered by molecular structure which invokes steric hindrance for OPs interaction with MPO active center responsible for peroxidase activity. In addition, it was concluded that physiological function of MPO is not affected by any of the investigated OPs.  相似文献   

12.
In vitro inhibition of electric eel acetylcholinesterase (AChE) by single and simultaneous exposure to organophosphorus insecticides diazinon and chlorpyrifos, and their transformation products, formed due to photoinduced degradation, was investigated. Increasing concentrations of diazinon, chlorpyrifos and their oxidation products, diazoxon and chlorpyrifos-oxon, inhibited AChE in a concentration-dependent manner. IC50 (20 min) values, obtained from the inhibition curves, were (in mol/l): (5.1 ± 0.3) × 10−8, (4.3 ± 0.2) × 10−6 and (3.0 ± 0.1) × 10−8 for diazoxon, chlorpyrifos and chlorpyrifos-oxon, respectively, while maximal diazinon concentration was lower than its IC50 (20 min). Calculated KI values, in mol/l, of 7.9 × 10−7, 9.6 × 10−6 and 4.3 × 10−7 were obtained for diazoxon, chlorpyrifos and chlorpyrifos-oxon, respectively. However, 2-isopropyl-4-methyl-6-pyrimidinol (IMP) and 3,5,6-trichloro-2-pyridinol, diazinon and chlorpyrifos hydrolysis products, did not noticeably affect the enzyme activity at all investigated concentrations. Additive inhibition effect was achieved for lower concentrations of the inhibitors (diazinon/diazoxon ?1 × 10−4/1 × 10−8 mol/l i.e., chlorpyrifos/chlorpyrifos-oxon ?2 × 10−6/3 × 10−8 mol/l), while an antagonistic effect was obtained for all higher concentrations of the organophosphates. Inhibitory power of 1 × 10−4 mol/l diazinon irradiated samples can be attributed mostly to the formation of diazoxon, while the presence of non-inhibiting photodegradation product IMP did not affect diazinon and diazoxon inhibitory efficiencies.  相似文献   

13.
In order to gain insight into the development of insecticides with novel modes of action, the effects of salicylidene aniline (a), salicylidene-4-chloroaniline (b), salicylidene-4-bromoaniline (c), and salicylidene-4-nitroaniline (d) on partially purified phenoloxidase (PO) from Pieris rapae L. were investigated. The results showed that the 4 compounds could inhibit PO activity, and the inhibitor concentrations leading to a loss of 50% activity (IC50) were estimated to be 0.025 mmol L−1, 0.732 mmol L−1, 0.471 mmol L−1, and 0.675 mmol L−1, respectively. Meanwhile, all the inhibitors showed reversible competitive inhibition, except (d), which showed reversible mixed inhibition. The KI values were determined as 0.106 mmol L−1, 10.059 mmol L−1, 8.390 mmol L−1, and 20.198 mmol L−1 for the four compounds, respectively. The UV-vis spectra of (a) and (d) in the presence of copper ions and the enzyme showed that (a) could directly chelate the copper ions of PO; however, (d) could neither chelate the additional copper ions nor the copper ions of PO.  相似文献   

14.
Trehalase, with the target to control insects, nematodes and fungi, is of increasing interest and has been investigated extensively in recent years. Validamycin compounds, as competitive trehalase inhibitors and lead compounds with broad applications have attracted substantial attention as well. In this study, the characterizations of termites trehalase were investigated and the inhibitory effects of validamycin compounds on the termites trehalase were studied as well. Results showed that the termites trehalase is presumably belonging to the acid trehalase with optimal pH of 3.3 and optimal temperature of 37 °C. It was investigated that the concentrations of validoxylamine A (VAA), validoxylamine B (VBB), validamycin A (VA) and validamycin B (VB) required for 50% inhibition IC50 of termites trehalase were calculated to be 14.73 mg l−1, 20.80 mg l−1, 3.17 × 103 mg l−1and 2.24 × 103 mg l−1, respectively. The inhibition kinetic constant Ki values for the above validamycin compounds were 3.2 × 10−6 mol l−1, 1.03 × 10−5 mol l−1, 4.02 × 10−4 mol l−1and 2.69 × 10−4 mol l−1, respectively. Validoxylamine A appeared to be the most potential termites trehalase inhibitor among the four compounds.  相似文献   

15.
Valienamine, an aminocyclitol with similar configuration to α-glucose, has a strong inhibitory effect on α-glucosidase. α-Glucosidase plays an important role in insect carbohydrate metabolism. The inhibitory effect of valienamine on the enzymatic activity of honeybee (Apis cerana Fabr.) α-glucosidase was investigated. Our results show that valienamine inhibition of honeybee α-glucosidase was pH- and dose-dependent, but temperature-independent. Valienamine is shown to be a potent and competitive reversible inhibitor of honeybee α-glucosidase in vitro with an IC50 value of 5.22 × 10−5 M and Ki value of 3.54 × 10−4 M at pH 6.5, 45 °C. Valienamine has the potential to be developed into novel insecticides.  相似文献   

16.
The features of two insecticides (chlorpyrifos and cypermethrin) binding to two blood proteins, bovine serum albumin (BSA), and bovine hemoglobin (BHb), were investigated via the fluorescence method. The results revealed that both insecticides caused the fluorescence quenching of BSA and the fluorescence enhancement of BHb. A new parameter (FE), i.e., the fluorescence intensity when adequate insecticide was added, was introduced to obtain the association constant (KA) and the number of binding sites (n). KA and n of chlorpyrifos and cypermethrin binding to BSA were 2.99 × 105 and 5.22 × 105 L mol−1, 1.25 and 0.78, respectively. KA and n of chlorpyrifos and cypermethrin binding to BHb were 2.94 × 104 and 2.48 × 104 L mol−1, 1.75 and 2.19, respectively. In conclusion, chlorpyrifos and cypermethrin could bind to BSA and BHb, and the binding of both insecticides to BSA was significantly stronger than that of insecticides to BHb. These could affect the distribution, metabolism, and excretion of insecticides.  相似文献   

17.
Elevated oxidative detoxification is a major mechanism responsible for pyrethroid resistance in Helicoverpa armigera from Asia. Constitutive overexpression of CYP9A12 and CYP9A14 was associated with pyrethroid resistance in the YGF strain of H. armigera. CYP9A12 and CYP9A14 were functionally expressed in the W(R) strain of yeast (Saccharomyces cerevisiae) transformed with a plasmid shuttle vector pYES2. The cell lysates prepared from yeast transformed with CYP9A12 and CYP9A14, respectively, exhibited considerable O-demethylation activities against two model substrates p-nitroanisole (0.59 and 0.42 nmol p-nitrophenol min−1 mg protein−1) and methoxyresorufin (2.98 and 5.41 pmol resorufin min−1 mg protein−1), and clearance activity against the pyrethroid esfenvalerate (8.18 and 4.29 pmol esfenvalerate min−1 mg protein−1). These results provide important evidence on the role of CYP9A12 and CYP9A14 in conferring pyrethroid resistance in H. armigera, and also demonstrate that the yeast expression system can provide necessary redox environment for insect P450s to metabolize xenobiotics.  相似文献   

18.
Multiwalled carbon nanotubes-polymeric methyl red film modified electrode (MWNT-PMRE) was made. The electrochemical behavior of carbendazim on modified electrode was studied with Cyclic Voltammetry, Linear Sweep Voltammetry, Stable Polarization Method and Chronocoulometry. The results indicated that the electrical oxidation of carbendazim on MWNT-PMRE in H2SO4 supporting electrolyte with concentration of 0.6 mol/L was irreversible and was mainly controlled by diffusion. Some parameters of the electrochemical process were evaluated. The impacts of experiment conditions on the electrochemical behavior of carbendazim were studied. A good linearity relationship between peak current and concentration of carbendazim in the range of 2.0 × 10−7-1.0 × 10−5 mol/L was found, of which the equation was Ip(A) = −1.149 × 10−5 − 2.301c (mol/L), the correlative coefficient R = −0.9953 and detection limit was 9.0 × 10−9 mol/L. The recovery was between 90.3% and 94.7%.  相似文献   

19.
Ecdysteroid signal transduction is a key process in insect development and therefore an important target for insecticide development. We employed an in vitro cell-based reporter bioassay for the screening of potential ecdysone receptor (EcR) agonistic and antagonistic compounds. Natural ecdysteroids were assayed with ecdysteroid-responsive cell line cultures that were transiently transfected with the reporter plasmid ERE-b.act.luc. We used the dipteran Schneider S2 cells of Drosophila melanogaster and the lepidopteran Bm5 cells of Bombyx mori, representing important pest insects in medicine and agriculture. Measurements showed an EcR agonistic activity only for cyasterone both in S2 (EC50 = 3.3 μM) and Bm5 cells (EC50 = 5.3 μM), which was low compared to that of the commercial dibenzoylhydrazine-based insecticide tebufenozide (EC50 = 0.71 μM and 0.00089 μM, respectively). Interestingly, a strong antagonistic activity was found for castasterone in S2 cells with an IC50 of 0.039 μM; in Bm5 cells this effect only became visible at much higher concentrations (IC50 = 18 μM). To gain more insight in the EcR interaction, three-dimensional modeling of dipteran and lepidopteran EcR-LBD was performed. In conclusion, we showed that the EcR cell-based reporter bioassay tested here is a useful and practical tool for the screening of candidate EcR agonists and antagonists. The docking experiments as well as the normal mode analysis provided evidence that the antagonist activity of castasterone may be through direct binding with the receptor with specific changes in protein flexibility. The search for new ecdysteroid-like compounds may be particularly relevant for dipterans because the activity of dibenzoylhydrazines appears to be correlated with an extension of the EcR-LBD binding pocket that is prominent in lepidopteran receptors but less so in the modeled dipteran structure.  相似文献   

20.
The inhibition of eel acetylcholinesterase and bovine erythrocyte acetylcholinesterase by the 4-nitrophenyl esters of methyl-, ethyl-, and isopropyl(phenyl)phosphinic acid (MPP, EPP, and IPP, respectively) was investigated at pH 6.90 in 0.067 M phosphate buffer (25.0°C) using stopped-flow instrumentation and automated data processing. Our evaluation of the dissociation constant, Kd, the unimolecular bonding rate constant, k2, and the bimolecular reaction constant, ki, are the first reported values for these constants for a homologous series of this class of organophosphorus compounds. The largest k1 value (29,428 M?1 sec?1) was observed for the reaction of eel acetylcholinesterase with 4-nitrophenyl methyl(phenyl)phosphinate. The smallest ki value (9.6 M?1 sec?1) was observed for the reaction of bovine erythrocyte acetylcholinesterase with 4-nitrophenyl isopropyl(phenyl)phosphinate.  相似文献   

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