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1.
Fifteen pesticides, representatives of different chemical groups, were tested for their inhibitory effect on the glucuronidation of 4-nitrophenol (4-NP) and phenolphthalein (PPh) by rat liver microsomes. Three herbicides (simazine, chlorsulfuron, tribenuron-methyl), two insecticides (dioxacarb, carbaryl) and one fungicide (zineb) significantly decreased the UDP-glucuronosyltransferase (UDPGT) activity. The carbamate insecticide dioxacarb was found to be the most potent inhibitor, at 1 mM concentration suppressing 4-NP-UDPGT activity completely, and reducing by 55% the activity associated with the conjugation of PPh. One millimole simazine and carbaryl affected only 4-NP glucuronidation, while chlorsulfuron and zineb exerted a marked inhibition of both 4-NP and PPh conversion. Concentrations of 0·1 mM carbaryl, dioxacarb and zineb were still inhibitory against 4-NP-UDPGT, with zineb producing 40% inhibition of PPh glucuronidation. As a whole, UDPGT isoforms conjugating PPh were less sensitive to the agrochemicals tested. Kinetic studies with dioxacarb, chlorsulfuron and carbaryl revealed a mixed type of inhibition with respect to the acceptor substrate 4-NP, with apparentKi values of 70 μM , 120 μM and 160 μM , respectively.  相似文献   

2.
Phenoloxidase (PO) is a key enzyme in the developmental process of insects that is responsible for catalyzing the hydroxylation of monophenols and the oxidation of o-diphenols. In the present investigation, the PO of Plutella Xylostella (L.)(Lepidoptera Plutellidae) was partially purified with 40% saturated (NH4)2SO4 and Sephadex G-100 gel filtration, and the effects of 4-dodecylresorcinol on the monophenolase and o-diphenolase activity of PO were studied. The results showed that 4-dodecylresorcinol could inhibit monophenolase and o-diphenolase activity. In addition, following 4-dodecylresorcinol treatments, the lag time of PO for oxidation of l-tyrosine was obviously lengthened and the steady-state activity was decreased. The inhibitor was found to be competitively reversible with a Ki of 0.201 mM and an estimated IC50 (inhibition concentration showing 50% of the maximum inhibition) of 0.160 mM for monophenolase and 0.369 mM for diphenolase. The ability of 4-dodecylresorcinol to inhibit PO activity may be associated with its ability to directly affect copper at the active site  相似文献   

3.
Properties of the phenoloxidase (PO) from adult of Gastrolina depressa Baly (Coleoptera: Chrysomelidae) as well as effects of some metal ions and inhibitors on the activity of PO purified by (NH4)2SO4 were determined. The optimal pH and temperature of the enzyme for the oxidation of catechol were determined to be at pH 7.5 and at 40 °C, respectively. The kinetic parameters for the oxidation of L-DOPA and catechol by the PO were 15.01 and 9.17 mM, respectively. The PO activity was strongly inhibited by Zn2+ and Cu2+, different to Mg2+ slightly. Both ascorbic acid and cysteine exhibited competitive inhibition and the inhibitory constants (Ki) were determined to be 2.22 mM and 0.40 mM, respectively.  相似文献   

4.
The kinetic constants, Kd, k2, and ki, were determined for the inhibition by 4-nitro-phenyl methyl(phenyl)phosphinate of three cholinesterases: butyrylcholinesterase, bovine erythrocyte acetylcholinesterase and eel acetylcholinesterase. Stopped-flow kinetic evaluations and automated data acquisition and processing were employed. A broad range in affinity for the phosphinate inhibitor was observed as reflected by the binding constants, Kd. A similar wide range in the k2 values for the unimolecular inhibition step was obtained. The net bimolecular rate constants, ki, indicate equal overall reactivity for butyrylcholinesterase and eel acetylcholinesterase with a smaller inhibition rate constant for bovine erythrocyte acetylcholinesterase.  相似文献   

5.
A series of 27 substituted aryl N-methoxy-N-methylcarbamates were synthesized and their ability to reversibly inhibit house fly-head and bovine-erythrocyte acetylcholinesterase and horse-serum cholinesterase was determined. These compounds were all competitive, reversible inhibitors of bovine erythrocyte acetylcholinesterase but some of them showed mixed competitive inhibition against the house fly-head and horse-serum enzymes. Dissociation constants (Ki) as small as 9.9 × 10?9M and as large as 1.4 × 10?4M were observed. A highly satisfactory correlation between log Ki for the inhibition of fly-head acetylcholinesterase by the N-methoxy-N-methylcarbamates and ?log I50 for the inhibition of the same enzyme by the corresponding methylcarbamates was noted. Analysis of the anticholinesterase data by multiple regression showed -log Ki to be related to Hansch's π constant and ring position terms. The results indicate that reversible binding of these compounds to acetylcholinesterase occurs by hydrophobic bonding.  相似文献   

6.
Butyrylcholinesterase (BChE), a major detoxification enzyme found abundantly in many tissues and organisms, constitutes the first line defense in the serum of higher organisms and is a marker for toxic exposure. In this study, the interaction of two plant growth regulators, indole-3-acetic acid (IAA) and chlorogenic acid (CA) with purified human and horse serum BChE is investigated. The time dependent interaction of IAA with the two enzyme species was concentration dependent and rapid. Through kinetic studies, IAA was found to be linear-mixed type inhibitor for human serum BChE, and uncompetitive inhibitor for the horse serum enzyme. For the human BChE, α and the Ki value was calculated as 2.15 ± 1.09 and 3.09 ± 0.98 mM, respectively, and for the horse enzyme the Ki value was calculated as 1.05 ± 0.09 mM. The time dependent interaction of CA with the two enzyme species was biphasic. At low CA concentrations, CA stimulated the activities of both enzyme species whereas at high CA concentrations, inhibition was observed. At high concentrations, the inhibition kinetics for both enzymes fitted the non-competitive inhibition model. The Ki values calculated for human and horse BChE were 2.75 ± 0.14 and 0.96 ± 0.07 mM, respectively. The differences in the interaction of these two growth regulators with the two enzymes species arises from the structural differences between the human and horse serum BChE which can be considered as a triple human mutant BChE.  相似文献   

7.
The effect of 2,4-dichlorophenoxyacetic acid (2,4-D), 4-chloro-2-methylphenoxyacetic acid (MCPA), and their derivatives: phenol, 2,4-dichlorophenol (2,4-DCP), 2,4-dimethylphenol (2,4-DMP), and catechol on the activity of acetylcholinesterase (AChE, EC 3.1.1.7) in human erythrocytes was studied. Phenol, MCPA, and 2,4-DMP did not significantly change AChE activity in human erythrocytes (in vitro). Decrease of AChE activity was observed under the highest applied dose of 2,4-D—500 and 1000 ppm. Decrease of AChE activity exposed to 2,4-DCP and catechol was noted and depended on the doses of applied compounds. The relationship between activities and substrate concentrations (curves) was analyzed for reactions of acetylcholinesterase. Catalytic constants Km and Vmax were calculated from the Michaelis curve. Statistically significant decrease of Vmax and Km was observed in the activity of AChE incubated with 2,4-DCP and catechol, revealing mixed inhibition type of AChE inhibition (this compound may affect not only on enzyme but also on complex ES as well). 2,4-D decreases Vmax but do not change Km value, what reveals non-competitive type of AChE inhibition by this compounds. Non-competitive inhibition does not depend on the substrate concentrations but only on the inhibitor concentration and its Ki value, characterizes the affinity of inhibitors towards enzyme. In conclusion, changes of AChE activity upon 2,4-D, 2,4-DCP, and catechol are the consequences of direct interactions between compounds and the enzyme and indirect via membrane modification and increase of Reactive Oxygen Species.  相似文献   

8.
The effect of nitroxynil, rafoxanide, diamphenethide, oxyclozanide and hexachlorophene on the malate dehydrogenase activity of homogenates of Fasciola hepatica was investigated. The ratio of oxaloacetate reduction to malate oxidation in homogenates of F. hepatica was 6.2:1. Nitroxynil, rafoxanide and diamphenethide had no inhibitory effect on malate dehydrogenase at 10?3 M . Oxyclozanide at 10?3 M inhibited malate oxidation by 100% and oxaloacetate reduction by 81%, while 10?3 M hexachlorophene inhibited activity in both directions by 100%. The inhibition quotient (K1 of bovine liver/Ki of F. hepatica) was 7.8 for oxyclozanide and 5.4 for hexachlorophene. No inhibition was seen with 2,4-dinitrophenol at 10?3 M . Rapid death resulted in vitro with 10?4 M oxyclozanide and 10?5 M hexachlorophene. Oxaloacetate reduction was inhibited 61% and malate oxidation 91% with oxyclozanide and 71 and 100% respectively with hexachlorophene. Slow death was also seen at 10?6 M concentration with both products although there was only 30% inhibition of malate dehydrogenase. Both products act as non-competitive inhibitors of malate dehydrogenase and this inhibition is more marked against the mitochondrial subcellular fraction than the cytoplasmic fraction.  相似文献   

9.
The plant defence activators acibenzolar-S-methyl (Benzo[1,2,3]thiadiazole-7-carbothioic acid-S-methyl ester, ASM), 2,6-dichloro-isonicotinic acid (DCINA), salicylic acid (SA), and dibasic potassium phosphate (K2HPO4) were tested for their ability to protect cashew (Anacardium occidentale) seeds and leaves from anthracnose disease caused by Colletotrichum gloeosporioides. No inhibition of the early stages of pathogen development was caused by concentrations equal to or lower than 1.1mM a.i. ASM, 1.2mM a.i. DCINA, 5mM SA and 50mM K2HPO4. Maximum reduction of the disease in detached leaves, without phytotoxic effects, was obtained with 0.07mM a.i. ASM and DCINA, 5mM SA, and 50mM K2HPO4, with a time interval of at least 72h between application of the activator and inoculation with the pathogen. On attached leaves, foliar sprays were slightly more efficient than soil drench treatments, with 5mM SA being the most effective treatment, while 50mM SA as well as 0.3mM a.i. ASM and DCINA caused phytotoxic effects. In field-grown plants, protection was conferred by a soil drench of concentrations as low as 12.6M a.i. ASM and DCINA and 2.6mM SA. These concentrations were not phytotoxic suggesting that plant defence activators have potential for control of anthracnose disease in the field.  相似文献   

10.
The firefly luciferase ATP assay was inhibited by the herbicide, isopropyl-3-chlorocarbanilate (I), and by two of its hydroxylated metabolites, isopropyl-5-chloro-2-hydroxycarbanilate (II) and isopropyl-3-chloro-4-hydroxycarbanilate (III). The β-O-glucosides of II and III reversed the inhibition of luciferase. Compounds I and II were linear noncompetitive inhibitors in respect to ATP (Ki ? 20 μM, each) and were linear competive inhibitors in respect to d-luciferin (Ki ? 6 μM, each). Compound III was a linear competitive inhibitor in respect to both ATP and d-luciferin (Ki ? 1 and 6 μM, respectively). The inhibition caused by III appeared to remain competitive for both substrates when AMP was added to the system, but the inhibition exhibited by III with respect to ATP and d-luciferin was more effective (Ki ? 0.5 μM, each). The effects of compounds I, II, and III upon the firefly luciferase ATP assay are discussed, and a relationship between the firefly system and plant susceptibility to compound I is proposed.  相似文献   

11.
The synthesis of several derivatives of a pesticide and an α-amino acid are described. The process involves three steps, the last one (deprotection of the α-amino acid group) being the most critical. The resulting products preserved their α-amino acid group and were globally neutral. They were tested for their effect on the transport of a neutral amino acid, threonine, and two sugars, sucrose and glucose. Two derivatives markedly and specifically inhibited threonine uptake by leaf tissues of Vicia faba L. and phloem loading. Preliminary experiments suggested that the lysine-2,4-D derivative is a competitive inhibitor of threonine uptake. The apparent Ki (0.5 mM) was much lower than the apparent Km (3 mm) of the natural substrate.  相似文献   

12.
A semi-open circuit system for measuring changes in net CO2 exchange (NCE) in single leaves of intact grasses following herbicide treatment is described and evaluated. There were significant differences in levels of inhibition and subsequent recovery of NCE in maize and eight weedy panicoid grasses following limited root uptake of atrazine (2-chloro-4-ethyl-amino-6-isopropylamino-1,3,5-triazine). cyanazine [2-chloro-4-(1-cyano-1-methylethylamino)-6-ethylamino-1,3,5-triazine] and cyprazine (2-chloro-4-cyclopropylamino-6-isopropyl-amino-1,3.5-triazine). Rate of NCE recovery was positively correlated (P = 0.05) with growth of seedlings in nutrient solution containing the herbicides. Rates of NCE recovery >0.9 mg CO2 per dm2 per h/h reflected rapid rates of herbicide detoxification in the leaves and a significant tolerance to preplant incorporated and postemergence applications of atra-zine, cyanazine and cyprazine. In contrast, some species, e.g. large crabgrass [Digitaria sanguinalis (L.) Scop.] and proso millet (Panicum miliaceum L.) treated with cyanazine demonstrated considerable tolerance to these treatments in spite of low NCE recovery rates indicating that factors other than foliar detoxification may play an important role in the tolerance of some grasses to 2-chloro- 1,3,5-triazine herbicides.  相似文献   

13.
为了探索天然产物Cedarmycins衍生物的结构与活性关系,以α-亚甲基-β-羟甲基-γ-丁内酯为起始原料,经过与不同取代的羧酸缩合,合成了19个新的(4-亚甲基-5-羰基-3-四氢呋喃基)-苯甲酸甲酯衍生物。杀菌活性测定结果表明,该类衍生物具有广谱的杀菌活性,尤其对水稻纹枯病菌Rhizoctonia solani和辣椒疫霉Phytophthora capsici显示出很强的杀菌活性,其中化合物2e(R=2,4-2Cl)对这2种病菌的EC50值约为1.6 mg/L。  相似文献   

14.
Plants of Amaranthus cruentus and Amaranthus hybridus resistant to atrazine and cyanazine were found in maize fields in north-eastern Spain. Both resistant foiotypes survived doses of 5 kg ha?1 of atrazine and 2–4 kg ha?1 of cyanazine but were controlled by lower doses of bentazone and pyridate than were susceptible biotypes. Such a negative cross-resistance was not found for chloroacetamides and MCPA. Chlorophyll fluorescence studies revealed that atrazine, bentazone, cyanazine and pyridate (10 mg litre?1) caused inhibition of photosynlhetic electron transport in susceptible leaves, while in resistant plants, atrazine and cyanazine had no effect. Conversely, bentazone and pyridate inhibited photosynthesis to a greater extent in resistant than in susceptible biotypes. Isolated chloroplast membranes from resistant biotypes showed resistance factors of 366 and 501 to atrazine and 39 and 60 to cyanazine for A. hybridus and A. cruentus, respectively. Bentazone and pyridate were found to be more effective in chloropiasts of the resistant biotypes than those of the susceptible plants. It is suggested that enhanced susceptibility to bentazone and pyridate in triazine-resistant A. cruentus and A. hybridus biotypes may be associated with the alteration of the D-I polypeptide subunit of photosystem II, as found in triazine-resistant plants.  相似文献   

15.
When methyl parathion is added at a given concentration to exponentially growing Chlorella cultures containing different numbers of cells, the inhibition of cell number, packed cell volume, pigment content, or photosynthesis has been found to be a function of the cell number, the inhibition being decreased with increased number of cells. Inhibition of photosynthesis has been studied further with a view to characterizing the mechanism of inhibition with a simple assumption that methyl parathion binds to a specific component in Chlorella cells to form an inhibitory complex. The concentration of methyl parathion causing 50% inhibition (I50) of photosynthetic O2 evolution increases linearly with increasing concentration of chlorophyll in the culture medium. With whole cells the inhibition constant (Ki) is 15 times greater than that with cell-free photosynthetic membranes. This shows that the cell wall acts as a permeability barrier. The relation between the I50 and Ki values and the analyses of the Hill plot of the inhibition curves reveal one binding site per 0.5 chlorophyll molecule and a cooperative binding of methyl parathion with at least three binding sites per binding molecule. Mild treatment of the photosynthetic membranes with trypsin makes the photosynthetic electron transport insensitive to the insecticide, suggesting that the binding component is proteinaceous in nature and the binding sites are located on the external surface of the membrane. The reversal of methyl parathion inhibition is parallel to that of 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (diuron) inhibition during trypsin treatment suggesting that the binding proteins for these two inhibitors are similar.  相似文献   

16.
The toxicological and biochemical characteristics of acetylcholinesterases (AChE) in Liposcelis paeta Pearman were investigated in three field populations collected from Nanyang city of Henan Province (NY), Wuzhou (WZ) and Hezhou (HZ) Cities of Guangxi Province, China. The result of bioassay showed that the LC50s of the NY (281.4802 mg/m2) and the WZ (285.0655 mg/m2) to dichlorvos were 1.156-fold and 1.171-fold higher than that of the HZ (243.5197 mg/m2), respectively. Compared to NY population, the activity per insect and the specific activity of AChE in WZ and HZ populations were significantly higher, and significant kinetic differences among the three populations were also observed. The apparent Michaelis–Menten constant (Km) for acetylthiocholine iodide (ATChI) was obviously lower in NY than that in WZ and HZ populations, indicating a higher affinity to the substrate ATChI in the NY population. The affinity to the substrate ATChI between WZ and HZ population was also significantly different. As for Vmax, the values of WZ and HZ populations were significantly greater when compared to that for NY population, suggesting a possible over expression of AChE in the former two populations. The inhibition studies of AChE indicated that paraoxon-ethyl, demeton-S-methyl, carbaryl, and eserine all possessed some inhibitory effects on AChE in L. paeta. The results of I50S suggested that when compared to the other two populations, while AChE from HZ population was less sensitive to paraoxon-ethyl and demeton-S-methyl. The contradiction with the result of the bioassay might be due to the different insecticides used in the bioassay. Although both carbaryl and eserine had excellent inhibitory effects, there was no significant difference among the three populations. The statistical analysis of the bimolecular rate constants (ki) was consistent with the above situation that carbamates expressed remarkable inhibitory effects. It was noticeable that NY population was most sensitive to carbaryl while least to eserine. The differences in AChE among three populations may attribute to the difference in control practices for psocids between Henan and Guangxi Provinces.  相似文献   

17.
The effects of abamectin (AVMB1) on intracellular potassium ion activity (aKi) and resting membrane potential (Em) of the skeletal muscle cells of final instar larvae of Phormia terraenovae (Diptera) were investigated using K+-selective micro-electrodes. Bathing the preparation in 10? M AVMB1(+ 1 ml litre?1 dimethylsulfoxide) for 60 min caused a significant (31%) decrease in aKi, whilst Em depolarized on average by 19 mV (nearly 50% of the original control value). The difference EK-Em increased by 9 mV, although EK (potassium equilibrium potential) remained more negative than Em. These results could be due to a cationic effect of AVMB1 possibly involving an increase in K+ and Na+ conductances of the muscle plasma membrane.  相似文献   

18.
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   

19.
4-chloroaniline was oxidized by soya cell-wall peroxidases in the presence of hydrogen peroxide. The main product, an orange compound with a maximal absorbance at 455 nm, was probably 4, 4′-dichloroazobenzene. The optimum pH of the reaction was 4. Michaelis constants, determined as described by Dalziel, were 21 mM for 4-chloroaniline and 94 μM for hydrogen peroxide. Syringaldazine was an uncompetitive inhibitor of 4-chloroaniline peroxidation (Ki =46 μM) and modified the progress of the reaction with the appearance of a lag period. By contrast, 4-chloroaniline was a non-competitive inhibitor of syringaldazine peroxidation with a Ki value of 21 mMx at pH 7.5. Therefore, these two inhibiting effects were compatible with the presence of two binding sites for two different hydrogen donors. Both sites were linked by allosteric interactions. The inferences on chloroaniline binding are discussed.  相似文献   

20.
Inhibitors of branched-chain amino acid biosynthesis—by inhibiting acetolactate synthase (ALS)—represent the most active group of herbicidal compounds to date (Shaner, D.L., Recent Adv. Phytochem. 23 (1989) 227–61). A microbial screening technique has been developed to investigate known and possible new ALS-inhibitors. Escherichia coli mutant FD 1062, which expresses only valine-resistant ALS II isoenzyme as the solely branched-chain amino acid synthesizing isoenzyme, has been used extensively to optimize known and to screen for new chemical classes of ALS-inhibitors, respectively. Herbicidal compounds like sulfonylureas, triazolopyrimidines, pyrimidylsalicylates, carbamoylpyrazolines, sulfonylimino-azinyl-heteroazoles, sulfonylamide azines, and substituted sulfonyldiamides, respectively, are active on minimal medium with Ki-values which resemble the rank order of biological activity of these compounds in the greenhouse. Interestingly, herbicidal imidazolinones are not at all inhibitory on E.coli strain FD 1062 in vivo although, of course, they exert high activity on isolated bacterial ALS. Similarly, N-protected valylanilides, pyrimidyl mandelic acids, benzenesulfonyl carboxamides, and uhiquinone-O are inactive in the bacterial assay but have been shown by other methods to act as ALS inhibitors. Additionally, reversal experiments can he performed to exclude, e.g. artificial inhibitory effects of test compounds. Moreover, a thin-layer biogram application technique opens the opportunity to test mixtures of chemicals. From green plant cell cultures (Catharanthus roseus) ALS has been isolated and characterized in terms of inhibition by sulfonylureas, imidazolonones, triazolopyrmidines, salicylated, and carbamoylpyrazolines, imidazolinones, triaiolopyritnidines, salicjdates, and carbarnoylpj?razolines, respectively. All five types show biphasic slow tight binding kinetics with Stedy state I50values of 0.5 nm (sulforneturon), 1.9 nm (triazolopjirimidine), 8.3 nm (salicylate), 23 nm (imazapyr), and 135 nm (carbamoylpyrazoline),respectiuely . Isolated ALS from Saccharomyces cerevisiae is equallv well blocked by herbicidal ALS inhibitors although with different I50values ( triazoiopyrimidine, 21 nm, sulforneturon, 70 nm, salicylate, 21 μm, imaiapyr, 38μm, and carbamoylpyrazoline, 148 μm ). Surprisingly, biphasic kinetics could not be observed with the yeast enzjtme although slow binding hehauiour was clearly established.  相似文献   

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