The effect of ronnel and its oxygen analog on succinate oxidation by rat brain,liver homogenates,and mitochondria

The effect of the thiophosphoroorganic insecticide ronnel and its oxygen analog on oxygen consumption by homogenates, and on succinate dehydrogenase and cytochrome oxidase activities in the mitochrondrial fractions of rat brain and liver, was investigated. A marked inhibition of blood plasma cholinesterase activity by the oxygen analog was demonstrated, but acetylcholinesterase activity was not affected. In contrast to its thiophosphoroorganic precursor, the oxygen analog caused a significant decrease in oxygen consumption by rat brain and liver homogenates and a decrease in cytochrome oxidase activity in both solubilized mitochondrial fractions. The succinate dehydrogenase activity was reduced only slightly by the oxygen analog in the brain fraction, but was marked in the liver fractions. The results suggest that the toxic activity of ronnel in vivo may be ascribed to its oxygen analog which appears as a metabolite of the former.     

Paraoxon formation and hydrolysis by mammalian liver

In vitro studies of the desulfuration of parathion at 37°C by hepatic tissue from males and females of nine mammalian species revealed sex and species variation in initial rates of parathion desulfuration and arylesterase-catalyzed hydrolysis of the oxygen analogue, paraoxon. Double reciprocal plots of initial rates of parathion activation for representative males and females of each species gave K_m values ranging from 0.2 × 10^?4?1.0 × 10^?4M parathion. Guinea pigs and rats were the only animals showing sex differences in activation, males possessing higher desulfurating abilities than the corresponding females. Based upon the sex possessing the higher desulfurating ability, the species pattern of decreasing activity was hamster > guinea pig > mouse > rat > rabbit > bovine > dog > porcine > cat. Studies of paraoxon hydrolysis indicated that only rats showed sex differences in hydrolysis, males possessing higher arylesterase activity than females. The species pattern of decreasing hydrolytic activity was in the order mouse > bovine > rat > guinea pig > rabbit > hamster > cat > dog > porcine.     

Selective inhibition of the metabolism of diazinon and diazoxon in vitro by piperonyl butoxide,NIA 16824, and 1-(2-isopropylphenyl)imidazole

Several pesticide synergists known to be mixed-function oxidase inhibitors were found to inhibit the in vitro metabolism of diazinon by mouse liver microsomes. Piperonyl butoxide and NIA 16824 (O-isobutyl-O-propargyl phenylphosphonate) inhibit all oxidative reactions of diazinon to the same extent. In contrast, 1-(2-isopropylphenyl)imidazole selectively inhibits oxidative dearylation and thiophosphate to phosphate conversion without significant effect on ring side chain hydroxylation. This selectivity suggests that two different mechanisms of oxidative detoxification may be operating, mechanisms which may involve either two cytochrome P-450s or two different binding sites on the same cytochrome.     

Inhibition of epoxidation of methyl farnesoate to juvenile hormone III by cockroach corpus allatum homogenates

Radiolabeled methyl farnesoate is epoxidized to juvenile hormone III by an NADPH-dependent reaction occurring in corpus allatum homogenates from the cockroach Blaberus giganteus L. Most of the enzymatically produced juvenile hormone has the 10R configuration described for previously isolated natural juvenile hormones. The unnatural 2Z geometrical isomer of methyl farnesoate is epoxidized by the above system faster than the natural 2E isomer. Several series of chemicals known to be inhibitors of mixed-function oxidases were surveyed as inhibitors of methyl farnesoate epoxidation. The anti-juvenile hormone precocene II caused negligible inhibition at 1 · 10^?4M, whereas the best inhibitor was o-bromophenoxymethyl-imidazole with an apparent I₅₀ of 4 · 10^?7M. None of the inhibitors tested were potent morphogenetic agents on Tenebrio molitor pupae, and they failed to cause precocious development of Oncopeltus fasciatus nymphs. The inhibition of in vitro juvenile hormone biosynthesis suggests the possibility of finding an anti-hormone which acts by blocking juvenile hormone biosynthesis.     

人参锈腐病菌毁灭柱孢菌酶促降解人参皂苷研究

皂苷被认为是植物抵抗病原真菌侵袭的防御物质,具有抗真菌活性.许多成功侵染植物的真菌通过产生皂苷解毒酶水解皂苷糖链上的糖残基,解除皂苷的毒性.本文研究了人参锈腐病菌毁灭柱孢菌Cylindrocarpon destructans和非人参病原菌构巢曲霉菌Aspergillus nidulans降解人参皂苷的能力.结果显示,毁灭柱孢菌能够产生胞外糖苷酶,水解二醇型人参皂苷Rb1、Rb2、Rc和Rd的C-3位和C-20位末端单糖,产生四种主要产物：绞股蓝皂苷XVII（G-XVII）、C-O、Mb和人参皂苷F2,而构巢曲霉菌只能将人参皂苷Rb1降解为Rd,不能降解其它的人参皂苷.这些结果说明,人参皂苷降解酶在毁灭柱孢菌的致病过程中可能发挥了重要作用.     

粪产碱杆菌ZWS11菌株对烟嘧磺隆的酶促降解特性

为明确粪产碱杆菌Alcaligenes faecalis ZWS11菌株对烟嘧磺隆的酶促降解特性,采用丙酮沉淀、超声波破碎和高速离心等方法,提取制备了ZWS11菌株的胞外和胞内粗酶液以及菌体碎片悬浮液,并分别测定了其酶活力。结果表明:当V（菌体发酵液）:V（丙酮）=1:3时提取到的胞外粗酶液具有较高的酶活力;胞外粗酶液、胞内粗酶液和菌体碎片悬浮液对24.9 μmol/L烟嘧磺隆的平均降解率分别为87.4%、16.9%和17.4%,胞外粗酶液的降解能力与胞内粗酶液或菌体碎片悬浮液相比差异显著（P<0.05）,由此确定对烟嘧磺隆起降解作用的酶属于胞外酶。最适降解条件研究表明:该降解酶的酶促反应适宜温度为35℃,较适pH值为6.0,反应时间为30 min,在此条件下其对烟嘧磺隆的降解率在80%以上。此外,该降解酶在35～70℃、pH值4.0～9.0范围内均能够保持较高的酶活力,对烟嘧磺隆的降解率均在60%以上,表明该降解酶具有较好的热稳定性和酸碱稳定性。加入不同浓度十二烷基硫酸钠（SDS）和苯甲基磺酰氟（PMSF）,对该降解酶的活力表现出了不同程度的抑制作用。研究结果可为烟嘧磺隆降解酶制剂的规模化生产及被烟嘧磺隆污染土壤的生物修复提供科学依据。     

Photolysis and hydrolysis of rimsulfuron

The degradation in the liquid phase of rimsulfuron and its commercial 250 g kg⁻¹ WG formulation (Titus®) was investigated. Photolysis reactions were carried out at 25 °C by a high-pressure mercury arc (Hg-UV) and a solar simulator (Suntest), while the hydrolysis rate was determined by keeping aqueous buffered samples in the dark. The effects of solvent and water pH on reaction kinetics were studied, and the results compared to literature data. Photoreactions of the commercial product in organic solvents were faster than pure rimsulfuron. Under simulated sunlight in water, the half-life for the photolysis reaction ranged from one to nine days at pH 5 and 9, respectively. The hydrolysis rate was as high as the photolysis rate, but decreased on increasing water pH. The main metabolite identified in neutral and alkaline conditions as well as in acetonitrile was N-[(3-ethylsulfonyl)-2-pyridinyl]-4,6-dimethoxy-2-pyridinamine, while N-(4,6-dimethoxy-2-pyrimidinyl)-N-[(3-(ethylsulfonyl)-2-pyridinyl)]urea and minor metabolites prevailed in acidic conditions. © 1999 Society of Chemical Industry     

Alcoholysis and chemical hydrolysis of bensulfuron-methyl

Alcoholysis (methanol or ethanol) and hydrolysis (pH ≤ 8) of the herbicide bensulfuron-methyl at 30 or 50^C involve only the breakdown of the urea part of the molecule. A high yield of the pyrimidinamine is always obtained, along with the corresponding carbamate (alcoholysis) or benzylsulfonamide (hydrolysis). The latter compound was easily cyclized (pH ≥ 6). In alkaline solution, the carbomethoxy substituent of the aromatic ring was preferentially hydrolysed. In all cases, the alcoholysis and hydrolysis rates could be described well with first-order kinetics. Alcoholysis rate constants of bensulfuron-methyl and bensulfuron ranged from 0.08 to 0.15 d^?1 at 30^C. Hydrolysis rate constants of bensulfuron-methyl, bensulfuron and benzylsulfonamide varied strongly with pH. The hydrolysis rate constant of bensulfuron-methyl was minimal around pH 8. The hydrolysis rate constant of bensulfuron decreased with increasing pH, whereas that of benzylsulfonamide increased with increasing pH.     

Soil catalysed hydrolysis of fluroxypyr-methylheptyl ester

Summary. Fluroxypyr-MHE (methylheptyl ester) was hydrolysed to fluroxypyr in soil/water suspensions at rates several thousand times that in distilled, deionized water at similar pH and temperature: the pH 7, 25°C half-life in water was 454days, compared to 2, 5, and 5·5 hours in 1 : 100 soil/water suspensions of a Barnes loam, Catlin silt loam, and Mhoon clay. The catalysed hydrolysis did not occur in decanted, aqueous supernatants of centrifuged Barnes soil suspensions, nor in Barnes soil/water suspensions which had been autoclaved. In soils incubated (26·1°C) at field moist conditions, only 1 to 2% of the fluroxypyr-MHE had not hydrolysed after three days. An extracellular enzyme was suggested as the catalyst.     

Effects of pyrethroid structure on rates of hydrolysis and oxidation by mouse liver microsomal enzymes

Studies on the metabolism rates of 44 pyrethroids and 24 model compounds in mouse liver microsomal systems serve to divide the substrates into three groups based on their ease of hydrolysis and oxidation. Primary alcohol esters of trans-substituted cyclopropanecarboxylic acids are most rapidly metabolized with hydrolysis generally serving as the major component of the total metabolism rate. Although hydrolyzed slowly or not at detectable rates, the primary alcohol cis-substituted cyclopropanecarboxylates, tetramethylcyclopropanecarboxylates, and p-chlorophenyl-α-isopropylacetates are rapidly oxidized. The highly insecticidal α-cyano-3-phenoxybenzyl esters are least susceptible to metabolic attack due to both reduced esterase rates attributable to α substitution in the alcohol moiety and reduced oxidase rates for which no adequate explanation is currently available. Other structural modifications in the acid and alcohol moieties are less important in determining the metabolism rates. The substrate specificities of the microsomal esterases and oxidases are compared with in vivo pyrethroid structure-biodegradability relationships.     

Maceration of plant tissue by fungi is inhibited by recombinant antipectinase antibodies

Polyclonal antiserum from mice immunized with extracellular proteins from Rhizoctonia solani inhibited pectinase and cellulase activities in cell free culture supernatants of Rhizoctonia solani. Spleen mRNA from these mice was used to construct a cDNA library from which antipectinase ScFv antibodies were isolated using phage display techniques. Soluble ScFv antibodies produced by individual clones in Escherichia coli inhibited polygalacturonase in the culture supernatants of a range of fungal pathogens, including ascomycetes, basidiomycetes, and oomycetes. The soluble antibodies also inhibited maceration of potato tissue by these pathogens.     

The inhibition of HEOM epoxide hydrase in mammalian liver microsomes and insect pupal homogenates

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.     

Multiple forms of esterases in mouse,rat, and rabbit liver,and their role in hydrolysis of organophosphorus and pyrethroid insecticides

Six to seven esterases from mouse, rat, and rabbit liver microsomes were resolved by chromatofocusing in the pH range 7–4. Each esterase peak showed a different substrate specificity pattern with the substrates evaluated. Malathion and paraoxon hydrolysis always corresponded with p-nitrophenyl acetate and methylthiobutyrate hydrolysis, whereas the pattern of fenvalerate hydrolysis was more complicated. Phosphorotriester hydrolase activity was isolated, and was found to be more specific toward paraoxon than toward the other insecticides. Time-course studies of paraoxon hydrolysis indicated that the hydrolysis of paraoxon by carboxylesterase was an inhibitory reaction. This reaction and phosphorotriester hydrolase activity can serve as a detoxication reaction toward organophosphate insecticides.     

Enzymatic Activity of the Mycelium Compared with Oospore Development During Infection of Pea Roots by Aphanomyces euteiches

ABSTRACT To describe the disease cycle of the root pathogen Aphanomyces euteiches, enzymatic activity in the mycelium was compared with the development of oospores in pea roots. Plants were inoculated with two zoospore concentrations to achieve different disease levels. Hyphae were stained for fungal alkaline phosphatase activity in the roots. Additionally, enzyme activity was measured after electrophoresis of an A. euteiches-specific glucose-6-phosphate isozyme. Development of oospores in the roots was measured after staining the oospores with trypan blue. In plants inoculated with the higher zoospore concentration, the enzymatic activity of the pathogen mycelium peaked 10 to 14 days after inoculation, when oospore formation was initiated. Oospore formation was associated with a gradual increase in disease symptoms. At the last harvest, plants inoculated with the higher zoospore concentration had died. In these plants, oospores were found in 90% of the root length, while the enzymatic activity of the mycelium was low. This suggests that the pathogen mycelium is only active on living plants and does not grow saprophytically on dead plant material.     

Kinetics and mechanism of the hydrolysis of imidacloprid

The kinetics of the hydrolysis of imidacloprid were studied at different pH values and under various temperatures. Imidacloprid was found to be stable in acidic and neutral water, but readily hydrolysed in alkaline water. The main hydrolysis product was found to be 1-[(6-chloro-3-pyridinyl)methyl]-2-imidazolidone, and a mechanism for its formation is proposed. © 1999 Society of Chemical Industry     

Kinetics and hydrolysis mechanism of chlorsulfuron and metsulfuron-methyl

In acidic media, hydrolysis of chlorsulfuron and metsulfuron-methyl occurs via two consecutive reactions which were followed by ultraviolet spectrophotometry. For these two reactions, the pseudo-first-order rate constants increase proportionally to the concentration of hydronium ion in the more acidic media and to the square of this concentration at higher pH values. A kinetic study by HPLC shows that the first reaction leads to the formation of 4-methoxy-6-methyl-1,3,5-triazin-2-amine and (o-chlorophenylsulfonyl) carbamic acid for chlorsulfuron or (o-methoxycarbonylphenylsulfonyl) carbamic acid for metsulfuronmethyl. The second reaction is the conversion of these sulfonylcarbamic acids to sulfonamides and carbon dioxide. The complete lack of saccharin and of o-sulfamoyl benzoic acid proves that the ester function of the methoxycarbonyl group is stable. The lack of general acid-base catalysis and a solvent deuterium isotope effect less than unity are consistent with a rate-determining cleavage of the protonated substrate. In the basic pH range (10–14) a single reaction occurs, the nucleophilic substitution of the methoxy group on the triazine by a hydroxide group.     

3,5-二氯苯胺在水中的光解及水解特性

3,5-二氯苯胺(3,5-DCA)是二甲酰亚胺类杀菌剂(DCFs)在环境和植物中的主要降解代谢产物,比其母体化合物具有更强的毒性和持久性。本研究通过室内模拟试验,利用气相色谱-质谱联用仪(GC-MS)和高效液相色谱(HPLC),研究了3,5-DCA的光解和水解特性。结果表明：初始质量浓度为5 mg/L的3,5-DCA在氙灯和紫外灯下光解的半衰期分别为49.5和11.6 min;在中性、酸性和碱性条件下光解的半衰期分别为9.9、168和10.7 min;在甲醇、乙腈、正己烷中光解的半衰期分别为4.10、2.69和0.58 h。进一步研究发现,3,5-DCA在正己烷中的光解产物为单脱氯产物。3,5-DCA在中性、酸性和碱性条件下的水解半衰期分别为40.8、77.0和86.6 d。不同浓度的表面活性剂十二烷基磺酸钠(SDS)和十六烷基三甲基溴化铵(CTAB)溶液均可抑制3,5-DCA的水解,其中CTAB的抑制效果强于SDS。研究结果有助于更全面地了解二甲酰亚胺类杀菌剂的环境归趋,可为其合理使用及环境安全性评价提供数据支持。     

酰基高丝氨酸内酯酶SS10的酶学特性及其抗软腐病功能的初探

 N-酰基高丝氨酸内酯(AHLs)作为细菌群体感应中的信号分子参与调节植物病原细菌致病因子的表达。N-酰基高丝氨酸内酯酶(简称AHL内酯酶)通过水解AHL生成酰基高丝氨酸, 使AHL失去活性, 阻断病原菌的群体感应机制, 使病原菌失去致病力。利用谷胱甘肽-琼脂糖亲和层析柱和凝血酶处理获得纯化的重组AHL内酯酶SS10, 分子量约为28 kD, 其反应的最适pH值为8.0, 在30℃以下稳定性很高。动力学和底物特异性分析表明:AHL内酯酶SS10对所检测的8种AHL具有很强的催化活性, 表明该酶的底物谱可能较宽, 并且具有催化裂解酰基高丝氨酸内酯键的特异性。纯化的AHL内酯酶SS10可以显著降低胡萝卜软腐欧文氏菌胞外果胶酶、多聚半乳糖醛酸酶的产生量。致病性测定表明, 该重组蛋白对胡萝卜软腐病菌具有较强的抗病活性。     

腐霉利的光解及水解特性研究

为研究腐霉利的消解特性,采用乙腈提取,弗罗里硅土柱净化,建立了油菜叶片中腐霉利残留的气相色谱-电子捕获检测器 (GC-ECD) 分析方法;并在室内模拟条件下,研究了腐霉利在油菜叶片表面的光解行为,以及不同初始浓度、不同pH值缓冲液、不同浓度Fe2+、Fe3+ 和NO₃–、NO₂– 对水溶液中腐霉利光解的影响;通过气相色谱-电子轰击电离源质谱仪 (GC-EIMS) 鉴定了其在甲醇、丙酮和乙腈溶液中的光解产物;同时研究了不同pH值缓冲液和阴、阳离子表面活性剂对腐霉利水解特性的影响。结果表明:腐霉利添加水平为0.05、0.2、2及12 mg/kg时,其在油菜叶片中的平均回收率为80%~100%,相对标准偏差为2.3%~7.8%。腐霉利在油菜叶片表面的消解动态符合一级动力学方程,紫外灯下的消解半衰期为1.03 h。腐霉利在水溶液中的光解速率随其初始浓度的升高而减慢;其在酸性条件下稳定,碱性条件下易光解;NO₃–、NO₂–、Fe2+ 及Fe3+均可抑制腐霉利在水溶液中的光解,因此可用作为其光猝灭剂。共鉴定出两种腐霉利在甲醇、丙酮和乙腈溶液中的光解产物,分别为其单脱氯化产物C₁₃H₁₂ClNO₂和其脱甲基化产物C₁₂H₉Cl₂NO₂。腐霉利在碱性条件下易水解,酸性条件下水解较慢;阴离子表面活性剂十二烷基磺酸钠 (SDS) 对其水解无影响,而阳离子表面活性剂十六烷基三甲基溴化铵 (CTAB) 则可促进其水解。研究结果可为腐霉利的合理使用及其环境安全性评价提供参考。