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1.
The effects on DNA synthesis of the fungicide captan and several structurally related compounds were investigated in isolated bovine liver nuclei. Captan, folpet, captafol, and trichloromethanesulfenyl chloride inhibited DNA synthesis to the same degree with ID50 values of approximately 50 μM in a 40-min assay. The inhibition is concentration dependent and the degree of inhibition increases with time. Studies with structural analogs of captan indicated that inhibition of DNA synthesis by captan is mediated through the trichloromethylthio moiety of the captan molecule. In addition, the data indicate thiophosgene is probably not the toxic species involved in the inhibition of DNA synthesis. The isolated nuclei used in this study were shown to exhibit only a single DNA polymerase activity which was determined to be of the β or low-molecular-weight type. In addition to its inhibition in intact nuclei, captan inhibited the activity of the β polymerase in nuclear extracts as well as in partially purified enzyme preparations. These results indicate that captan inhibits DNA synthesis in our preparation of isolated nuclei by acting directly on the DNA polymerase-catalyzed reaction rather than by causing a nonspecific or indirect effect in the nuclear system such as alterations in the nuclear membrane or aggregation of the nuclei. The site of captan's inhibitory action is the DNA polymerase molecule. The interaction of captan with the polymerase results in irreversible inhibition of the enzyme. Interaction of captan with the template, if it occurs, does not appear to be involved in mediating the inhibition.  相似文献   

2.
The reactions of captan, folpet, and thiophosgene with calf thymus histones and total rat liver histones were investigated. The binding of radioactivity from [35S]captan or [14C]folpet and changes in polyacrylamide gel patterns of captan-treated calf thymus histones were pH dependent. At pH 7.5, gel patterns of captan-treated histones were not different from those of non-treated histones; whereas, at pH 9.0 the Amido Schwartz-staining bands of captan- and thiophosgene-treated histones in polyacrylamide gels were characterized by band diffusion, loss of staining definition, band migration, and aggregate formation. Nearly equal amounts of radio-activity from [14C]folpet and [35S]captan were bound to lysine-rich histones at pH 9.0, while at pH 7.5 there was little binding of radioactivity to the proteins. Approximately equal amounts of radioactivity were removed from histones in the presence of the low-molecular-weight thiol, dithiothreitol. Reconstitution experiments using captan-treated lysine-rich histones and non-treated calf thymus DNA yielded less stable complexes, as well as smaller nucleohistone-nucleohistone complexes. These data suggest that the intact molecule binds to deprotonated sites on the lysine-rich histones. This binding causes changes in the configuration of the protein molecule which alters the ability of nuclear histones to stabilize DNA structure.  相似文献   

3.
Treatment of human erythrocytes with 5 × 10?5M captan or captafol caused a rapid increase in the efflux of intracellular potassium. Captafol had a more pronounced effect than captan on cation permeability. Captafol also decreased anion permeability whereas captan did not affect this process. Glutathione (5 × 10?4M) had little effect in reducing potassium efflux when added to the cells after they were incubated for 1 h with captan or captafol, but it was effective in reducing the potassium loss when added to the cells prior to their treatment with the fungicides. Captafol caused an increase in osmotic fragility of the cells. Incubation of the cell membranes with captafol resulted in the liberation of a small fraction of membrane phospholipids, whereas captan produced no effect. Both the fungicides readily reacted with the sulfhydryl groups in the isolated membrane; 31.5 and 45.7% of the membrane sulfhydryl groups had disappeared following treatment with captan and captafol, respectively. It is suggested that the reaction of captan or captafol and/or their reaction products with the sulfhydryl and amino groups of the red cell membrane protein produces changes in the structure of the membrane with consequent alteration in its permeability.  相似文献   

4.
In apterous adults of the spirea aphid, Aphis citricola van der Goot, the optimum conditions for determining acetylcholinesterase (AChE) activity consist of reaction mixture of 0.1 M phosphate buffer (pH 7.5), 10?3M acetylthiocholine (ASCh), and enzyme extract equivalent to 80 ± 3 μg protein incubated for 15 min at 30°C. The Km value for ASCh (6.7 × 10?5M) was much lower than that of butyrylthiocholine (BuSCh) (1.25 × 10?2M). The enzyme activity was almost completely inhibited by 10?6M paraoxon or 10?5M eserine and was 84% inhibited by 10?5M BW284C51 (a specific AChE inhibitor). DTNB was found to inhibit the enzyme activity and was therefore added at the end of the reaction. AChE activity of A. citricola was inhibited in vitro and in vivo by dimethoxon > dimethoate, and aldicarb sulfoxide > aldicarb > aldicarb sulfone. The in vivo effect correlates well with the toxicity level of the various toxicants. A neurotoxicity index which combines both mortality and in vivo inhibition of the aphid AChE activity is suggested as a measure for determining the toxicity of organophosphorus and carbamate compounds toward aphids.  相似文献   

5.
Methyl-1-(butylcarbamoyl)-2-benzimidazolecarbamate (benomyl) severely decreased DNA synthesis when applied at 3.5 × 10?6M during the G1 phase of germinating conidia of Fusarium oxysporum; nuclear divisions were completely inhibited at a fungicide concentration of 10 × 10?6M. The same concentration applied only after the S phase also completely inhibited the nuclear divisions. This dual interference of benomyl with DNA formation and mitosis might be related to a disturbed phosphorus metabolism.  相似文献   

6.
The binding behavior of mercuric chloride (HgCl2), phenylmercuric acetate (PMA), and ethylmercuric chloride (EMC) to the spinach chloroplasts in relation to the inhibition of the Hill reaction was studied at pH 6.8 and 7.8 using 203Hg labeled compounds. The pH of the reaction medium did not influence the amount of mercury binding of the chloroplast at various mercurial concentrations, but it altered the inhibition curve of the Hill reaction. Between 0–1 × 10?5M the binding of Hg2+ and EMC were similar and increased linearly with the concentration, while the binding of PMA was similar to the binding of Hg2+ only at a concentration below 4 × 10?6M and was less when the concentration was above 4 × 10?6M. However, the inhibition of the Hill reaction by these mercury compounds was quite different; at pH 7.8, the I50 values for Hg2+, PMA, and EMC were 5 × 10?6, 2.5 × 10?6, and 2.5 × 10?6M, respectively, while at pH 6.8, these values were 4 × 10?6, 4 × 10?5, and 2 × 10?4M, respectively. The differential block of electron flow by the mercury compounds at pH 6.8 and 7.8 was further confirmed by electron spin resonance study.  相似文献   

7.
At concentrations near 2 × 10?4M, barban, chlorpropham, and phenmedipham are inhibitors of the electron transfer in potato and mung bean mitochondria. The inhibition seems to be localized in the flavoprotein region. It affects preferentially the exogenous NADH dehydrogenation, in potato mitochondria (I50, 10?4M). Succinate dehydrogenation is less inhibited. At noninhibiting concentrations, the studied carbamates cannot uncouple the oxidative phosphorylations. Photosynthesis is completely inhibited by 2.10?7M phenmedipham, 5 × 10?5M barban, and 2 × 10?4M chlorpropham. The inhibition takes place at the PS II level. Moreover, barban and chlorpropham are uncouplers of the photophosphorylations for concentrations between 5 × 10?5 and 5 × 10?4M. The effects observed on mitochondrial respiration can also be found on respiration of Acer cultured cells. The effects on isolated chloroplast photosynthesis are also observed for slightly higher concentrations on cultured Chlorella and on pea and oat leaf fragments.  相似文献   

8.
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   

9.
A Ca-ATPase highly sensitive to DDT has been found in peripheral nerves of lobster, Homarus americanus. The observed I50 for this Ca-ATPase toward DDT is on the order of 10?9M and has a low temperature quotien. The ATPase seems to work over a wide range of ATP concentrations. It is stimulated by Ca2+ (optimum 0.1 mM) and shows sensitivity to Na+ (optimum 20 mM) and K+ (optimum 20 mM) ions. The fact that it is highly sensitive to ruthenium red (I50 = 10 μM) suggests that the enzyme is a Ca-ATPase and not a Mg-ATPase. Furthermore the enzyme is not a CaMg-ATPase, since the presence of Mg2+ along with Ca2+ ion is not required for its activity. DDT is found to inhibit the process of Ca2+ binding in the axonic membrane only in the presence of ATP. The evidence suggests the important role of the Ca-ATPase in regulating Ca2+ concentrations in the membrane. The possible significance of DDT inhibition of the ATPase is discussed.  相似文献   

10.
The activities of acetylcholinesterase, diacylglycerol kinase, and phosphatidylinositol phosphodiesterase in rat brain microsomes were measured in the presence and absence of the organophosphorus insecticides, parathion and diazinon, and their respective oxon analogs, paraoxon and diazoxon. Marked inhibition of acetylcholinesterase (by 45–99%) was observed in the presence of paraoxon (10?2–10?6M) and diazoxon (10?2–10?4M). Reduction of acetylcholinesterase activity (by 22–33%) was achieved with the parent insecticides at high concentrations only (10?2M). In most cases, diacylglycerol kinase was insensitive to the pesticides. Marked stimulation of phosphatidylinositol phosphodiesterase (by 10–57%) was observed in the presence of all pesticides (10?2–10?3M). The phosphodiesterase exhibited slightly greater sensitivity to the parent compounds compared to the oxon derivatives. Stimulation of the phosphodiesterase by the insecticides was not correlated with acetylcholinesterase inhibition. Accordingly, the increase in phosphodiesterase activity was judged not to be acetylcholine mediated, but rather represented a direct effect of the pesticides on the enzyme or its microenvironment. Based on the present in vitro observations, it is proposed that certain organophosphorus pesticides may interfere with the normal process of synaptic transmission through both the inhibition of acetylcholinesterase and the stimulation of phosphatidylinositol phosphodiesterase. In view of the high concentrations of pesticides required to elicit the latter effect, interpretation of its physiological significance must await results from further studies performed in vivo.  相似文献   

11.
A series of compounds containing the trifluoromethylketone group have been synthesized utilizing either a modified Grignard procedure or by reacting selected aliphatic bromides or tosylates with the Collman reagent [Na2Fe(CO)4]. When tested in vitro as inhibitors of crude juvenile hormone esterase from the hemolymph of the cabbage looper, Trichoplusia ni (Noctuidae), the most active compounds were trifluoromethylketones possessing either a juvenoid-like structure or a straight aliphatic chain. The logarithm of the inhibitory potency of the aliphatic compounds was proportional to their chain length, up to 1,1,1-trifluorotetradecan-2-one (I50 = 1 × 10?7M). This powerful inhibition was found to be highly selective for JHE, reversible, competitive by Lineweaver-Burk analysis, and was characterized by high affinity of the inhibitor for the esterase (Ki = 3.2 × 10?9M, Km JH III = 2 × 10?7M). Other trifluoromethylketones were shown to be inhibitors of T. ni α-naphthylacetate esterase and bovine trypsin. By analogy with the mechanism of trypsin action, trifluoromethylketones are probably potent inhibitors due to their resemblance to a tetrahedral transition state on the reaction coordinate to the acylated enzyme.  相似文献   

12.
The effects of two pesticides, dieldrin and captan, upon the growth and macromolecular syntheses of the vegetative cells of Dictyostelium discoideum strain Ax-2 were investigated. Dieldrin at a concentration of 5 μg/ml inhibited growth as well as the synthesis of RNA, DNA, and protein, while as little as 1 μg/ml of captan produced the same effects. After a 1-hr exposure to either pesticide, all macromolecular syntheses ceased. Within a period of 5 to 10 hr the amoebae began to shrink, and eventually some lysis occurred. Lysis was most pronounced in cells incubated with captan. When the amoebae were grown in the presence of 5 μg/ml of either pesticide and then washed and resuspended in fresh medium, the effects on growth were annulled. No growth inhibition was observed when 0.05 M cysteine was added prior to the addition of 5 μg/ml of captan. Further experimentation to study possible degradation effects of these two synthetic pesticides upon RNA and protein molecules showed that breakdown of these macromolecules into TCA-soluble units did not occur. Preliminary studies have also shown that [2-14C]uracil and [14C]amino acids are taken up in their respective pools in the presence of captan or dieldrin.  相似文献   

13.
Long-term experiments with dactyl cells of Nitella flexilis showed that the herbicide 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) at a concentration of 1 × 10?5M affected not only O2 evolution in the light but also O2 uptake in the dark. The inhibition of O2 production was transitory, but dark respiration did not recover. DCMU induced the formation of giant mitochondria which disappeared before cell death. It was concluded that the algicidic effect of 1 × 10?5M DCMU on N. flexilis, but not necessarily the elongation of mitochondria, was due to the inhibition of mitochondrial respiration and not of photosynthesis.  相似文献   

14.
A range of compounds were tested as inhibitors of the enzyme epoxide hydrase, using a cyclodiene epoxide (HEOM) as substrate. Rat and rabbit liver microsomes and pupal homogenates of the blowfly (Calliphora erythrocephala) and the yellow mealworm (Tenebrio molitor) were compared as sources of the enzyme. Only minor differences were found between the four enzyme preparations, when considering I50 values and percentage inhibition at standard concentration. The simple epoxide 1,1,1-trichloropropane-2,3-epoxide and two glycidyl ethers p-nitrophenyl glycidyl ether and p-ethylphenyl glycidyl ether tended to have lower I50 values (1.8×10?6 to 8.0×10?5M) than triphenyl phosphate and SKF 525A (4.5×10?5 to 1.4×10?4M). Triphenyl phosphate and SKF 525A were competitive inhibitors for both the rat and Tenebrio enzymes. The only clear difference found between these two epoxide hydrase preparations was with respect to their inhibition by 1,1,1-trichloropropane-2,3-epoxide, which was an uncompetitive inhibitor with the rat enzyme, but showed kinetics of mixed inhibition with the insect preparation.  相似文献   

15.
sec-Butylamine at 5 mM inhibited the oxidation of pyruvate by mitochondria isolated from hyphae of Penicillium digitalum, but had little effect on the oxidation of citrate, isocitrate, succinate, malate, acetyl-coenzyme A, or reduced nicotinamide adenine dinucleotide. sec-Butylamine did not interfere with oxidative phosphorylation, as evidenced by similar PO ratios in treated and control mitochondria. The pyruvate dehydrogenase complex (EC 1.2.4.1) isolated from young hyphae of P. digitatum was inhibited strongly by 20 mM sec-butylamine, whereas other tricarboxylic acid cycle enzymes were only slightly affected at most. Inhibition of the pyruvate dehydrogenase complex by sec-butylamine was competitive with respect to pyruvate. The Ki for sec-butylamine in the reaction was 1.38 × 10?2M, and the Km for pyruvate was 2.28 × 10?4M. These observations and other evidence derived from studies with intact hyphae support the hypothesis that the pyruvate dehydrogenase complex is the primary site of the fungistatic action of sec-butylamine.  相似文献   

16.
A “soluble” glutathione S-transferase that catalyzes the cleavage of the herbicide, 2,4′-dinitro-4-trifluoromethyl diphenylether (fluorodifen), was isolated and partially characterized from epicotyl tissues of pea seedlings. A 32-fold purification of the enzyme was achieved by differential centrifugation, ammonium sulfate precipitation, Sephadex gel filtration, and DEAE-cellulose ion exchange chromatography. The enzyme had a pH optimum of 9.3–9.5 and was specific for reduced glutathione, with an estimated apparent Km value of 7.4 × 10?4M. Limited specificity studies with four substituted 14C-labeled diphenylether compounds indicated that fluorodifen was the only effective substrate, with an estimated apparent Km value of 1.2 × 10?5M. Differences and similarities between the pea epicotyl enzyme and other plant and animal glutathione S-transferases were discussed from the standpoint of substrate specificity, pH optima, distribution, stability, and inhibitor studies.  相似文献   

17.
Some inhibition kinetic properties and in vivo inhibition of the plasma juvenile hormone esterase from the cabbage looper (Trichoplusia ni Hübner) by one phosphoramidothioate and two trifluoromethylketones were examined. O-ethyl,S-phenyl phosphoramidothioate was shown to react irreversibly with the enzyme in a time-dependent manner, and the inhibition reaction can be factored into a reversible step with a dissociation constant, Kd, of 4.55 × 10?5M followed by a phosphorylation step with a rate constant, k2, of 1.98 min?1. The phosphorylated enzyme did not show spontaneous recovery after 48 hr of dialysis. On the other hand, the two trifluoromethylketones were shown to act as reversible inhibitors, as their inhibited enzyme was regenerated completely after dialysis. However, 1,1,1,-trifluoro-3-thiooctylpropan-2-one, in contrast to 1,1,1-trifluorotetradecan-2-one, showed progressive time-dependent inhibition, and its reaction with the enzyme followed characteristic bimolecular second-order kinetics with a rate constant, ki, of 3.37 × 107M?1 min?1. The in vivo inhibition data of topically treated larvae at equimolar amounts of the tested compounds indicated rapid penetration, and the stability of the inhibition was higher for the phosphoramidothioate than for the trifluoromethylketones. The relationship of the mechanism of inhibition and the in vivo inhibition of these compounds to the understanding of the interactions between juvenile hormone and juvenile hormone esterase is discussed.  相似文献   

18.
The effects of chlordimeform on rectus abdominis muscle of frog were investigated. Chlordimeform (10?3M) caused a slow contraction, and at lower concentration (10?5–10?3M) it inhibited the acetylcholine-induced contraction in noncompetitive manner. When chlordimeform was applied to the muscle of Rana catesbiana, K+-induced contraction was also inhibited in noncompetitive manner. Whereas it had no effect on caffeine-induced contraction.Chlordimeform-induced contraction was not affected by respective addition of d-tubocurarine (10?4M), procaine (10?3M), or eserine (0.3 mM), which results were same as that of K+-induced contraction. Chlordimeform, at lower concentration (10?5–10?3M), inhibits the acetylcholine- and K+-induced contractions probably owing to depression of not only the sensitivity of endplate but also the excitability of cell membrane.  相似文献   

19.
Homogenates of three strains of Myzus persicae, A, R, and E, with an LD50 for topically applied parathion of 9, 93, and 263 ng per aphid, showed an in vitro hydrolytic degradation of paraoxon of 2.3, 4.7, and 8.6 pmol/mg aphid/h, respectively. These values represent Vmax; Km was <10?7M. The three strains showed a malaoxon degradation of 2.4, 11.9, and 18.8 pmol/mg/h at 10?6M substrate concentration. Vmax for R and E was 21 and 27 pmol, respectively and Km 7 and 4 × 10?7M. Activity in strain A was too low to estimate these entities. The breakdown product of paraoxon was mainly diethyl phosphoric acid, that of malaoxon mainly dimethyl phosphoric acid. No hydrolysis of the carboxylester groups of malaoxon was found. Hydrolysis of paraoxon and malaoxon was inhibited by isopropyl and n-propyl paraoxon and by the salioxon-analog K2. The two latter compounds were shown to act as synergists with parathion when added in amounts that caused little mortality when given alone. The hydrolytic enzyme is soluble and retains its activity during incubations of several hours. It is likely that it is responsible for at least part of the resistance. Resistance was maintained without selection over a period of three years. There was no correlation between degree of resistance and carboxylesterase activity of the strains.  相似文献   

20.
A suspension culture of isolated rat hepatocytes was used to reproduce in vitro the paraoxon-induced release of hepatic β-glucuronidase observed in vivo. After a short latent period, exposure of hepatocytes to paraoxon at 10?7 to 10?4M resulted in a typical dose-dependent response, with highest release occurring at 10?4M paraoxon. With 10?3M paraoxon, however, response was anomalous with a much-decreased enzyme release. As expected from earlier results in vivo, SV1-oxon exhibited less effect than paraoxon.  相似文献   

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