Isomerization and Beckmann rearrangement reactions in the metabolism of methomyl in rats

Methomyl {S-methyl-N-[(methylcarbamoyl)oxy]thioacetimidate}, also known as Lannate, may exist in two geometric configurations but the more stable syn isomer is the form applied as an insecticide. In the rat, syn[¹⁴CN]methomyl [CH₃S(CH₃)CNOC(O)NHCH₃] was metabolized to respiratory ¹⁴CO₂ and $\text{CH}{}_3{}^{14}\text{CN}$ in a ratio of about 2 to 1. Studies with the anti isomer showed that it was metabolized predominately to $\text{CH}{}_3{}^{14}\text{CN}$. These and other data are presented supporting the contention that syn methomyl is partially isomerized to the anti isomer in the animal prior to the hydrolysis of the ester linkage. After hydrolysis, the syn oxime [CH₃S(CH₃)¹⁴CNOH] is further metabolized to ¹⁴CO₂ while the anti oxime is metabolized to $\text{CH}{}_3{}^{14}\text{CN}$. Proposed immediate precursors to the carbon dioxide and acetonitrile, formed by Beckmann rearrangement of the syn and anti oximes, are CH₃S¹⁴C(O)NHCH₃ and $\text{[}\text{CH}{}_3{}^{\mathrm{14\oplus }}\text{CNSCH}{}_3\text{]x}{}^{\mathrm{?}}$, respectively.     

Spectral interactions of insecticide synergists with microsomal cytochrome P-450 from insecticide-resistant and susceptible house flies

The spectral interactions of 45 insecticide synergists and related compounds with oxidized and reduced cytochrome P-450 from microsomes of insecticide-resistant and -susceptible house flies were investigated. The type III interaction typical of piperonyl butoxide was the most common spectral interaction for the compounds studied. In addition to this, several other varients of the type III interaction were noted. In general these responses with house fly microsomes were similar to those reported for mammals, although some minor species and strain differences were observed. The cytochrome P-450 from susceptible house flies, although reported previously not to exhibit type I difference spectra with many xenobiotics, was found to elicit this spectral response with several methylenedioxyphenyl compounds.     

Biochemical genetics of oxidative resistance to diazinon in the house fly

The genetics and biochemistry of oxidative resistance to diazinon were investigated in a diazinon-resistant strain of the house fly, Musca domestica L. The resistant strain was crossed with a multimarker susceptible strain and substrains containing portions of the resistant strain genome were prepared. Resistance, microsomal oxidase, and cytochrome P-450 spectral characteristics were then compared in the different strains. The major gene for resistance to diazinon is semidominant and is located on chromosome II, 13 crossing over units from the recessive mutant stubby wing. Additional resistance genes occur on chromosome II and on other chromosomes as well. Resistance to diazinon was introduced into a susceptible mutant-marked strain via genetic crossing over. Increases in parathion oxidase, total and P-450-specific N- and O-demethylase activity, and resistant strain type I binding spectrum were introduced along with resistance, indicating genes controlling these parameters and resistance are either identical or closely linked. No increase in activity of cytochrome P-450 itself was introduced into the mutant strain. Additional genes controlling the amount of cytochrome P-450 and several spectral changes characteristic of the resistant strains are apparently controlled by genes located at different loci on chromosome II. Resistance factors on other chromosomes are also present, but were not characterized.     

Comparative enzyme activities and cytochrome P-450 levels of some rat tissues with respect to their metabolism of several pesticides

Cytochrome P-450, A- and B-esterase, amidase, and glutathione S-aryl transferase were assayed in the postmitochondrial centrifugal fraction, microsomes, and supernatant of rat liver, lungs, kidneys, and testes. Liver microsomes contained the highest P-450 levels and A-esterase activity. B-esterase activity was more generally distributed and higher in the microsomal tissue fractions. Microsomal amidase activity was highest in rat lung and lowest in the liver (per mg protein). Glutathione S-aryl transferase activity was highest in the liver. The in vitro metabolism of carbaryl, phosphamidon, and chlorotoluron by the various centrifugal fractions revealed many differences. Carbaryl metabolism was greater in the liver microsomal fractions than in any other preparation. 1-Naphthol was the major metabolite in all tissue fractions. Although very little metabolism of phosphamidon occurred in the rat, metabolism in the rat liver postmitochondrial fraction was slightly higher with respect to the production of metabolites than in the supernatant and microsomes combined. Chlorotoluron was not metabolized by any of the tissue fractions of the rat. At least a low level of activity toward some compounds was observed in all tissues, but this study confirmed that the liver was the most active metabolizing tissue as well as having the highest levels of enzymatic activity usually associated with pesticide metabolism.     

Balance of conversion of [14C]lindane in lettuce in hydroponic culture

After application of [¹⁴C]lindane to the nutrient medium (1.45 ppm), 14.1% of the radioactivity was taken up by 12 lettuce plants during 4 weeks; in the nutrient medium, 7.8% was recovered after the same time interval. The radioactivity in the nutrient extract comprised: unchanged lindane (about 82%); free 2,3,4,6-tetrachlorophenol, free pentachlorophenol, conjugates of pentachlorophenol, and an unidentified polar compound (a total of 15%); 1,2,3-trichlorobenzene, 1,2,3,4-tetrachlorobenzene, pentachlorobenzene, hexachlorobenzene, 2,3,4,5,6-pentachlorocyclohex-1-ene, and probably 1,2,3,4,5,6-hexachlorocyclohexene (a total of 3%). The radioactivity extracted from plants consisted of unchanged lindane (about 77%); free 2,3,4,6-tetrachlorophenol, conjugates of a tetrachlorophenol and pentachlorophenol, and a strongly hydrophilic compound that was not identified (a total of 20%); 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, pentachlorobenzene, 2,3,4,5,6-pentachlorocyclohex-1-ene, and probably 1,2,3,4,5,6-hexachlorocyclohexene (a total of 3%). Identification was carried out by means of comparisons of chromatographic properties and of the mass spectra with those of authentic reference compounds. The significance of hexachlorobenzene as a metabolite of lindane is discussed.     

Dissociation and phosphorylation constants for the inhibition of acetylcholinesterase by a series of novel O-ethyl O-phenyl S-n-propyl phosphorothioates

The phosphorylation, dissociation, and bimolecular reaction constants were determined for several members of a series of substituted O-ethyl O-phenyl S-n-propyl phosphorothioates in the presence of substrate. The data obtained are discussed in relation to electronegativity of substituents and in vivo toxicity.     

Biological Control of Take-all by Phialophora radicicola Cain1

Biological control of take-all by Phialophora radicicola Cain and similar fungi is reviewed, and new evidence is presented on the possible role of hyper-parasites, like Pythium oligandrum Drechsler, to augment this. Phialophora radicicola var. graminicola Deacon is abundant in British grasslands. Its role in biological control of take-all has been demonstrated in the glasshouse with natural soils and natural population levels of this control agent. Also there is much circumstantial evidence for its beneficial role in agriculture, especially in cereal monoculture following grass crops, and in natural and amenity grasslands. Some other similar fungi control take-all in the glasshouse, but their roles in current agricultural practice are not known. The take-all fungus, itself, can reduce infection of roots by P. radicicola, so there is a dynamic interaction between these fungi. This is affected by host type, relative inoculum potentials of the fungi, and possibly by environmental conditions. By careful manipulation, therefore, it might be possible to control take-all under a wide range of field conditions. The chief role of P. radicicola and similar fungi is to delay establishment of severe take-all early in cereal monoculture, rather than to combat an existing high disease level. It may therefore be desirable to combine different biocontrols, and hyperparasites like Pythium oligandrum may be important in this respect. This fungus was tested against varieties of Gaeumannomyces graminis Arx & Olivier and Phialophora radicicola in the laboratory; the host responses differed greatly, from marked susceptibility (P. radicicola var. radicicola) to almost complete resistance (G. graminis var. graminis). Hence, P. oligandrum might be used to alter relative population levels of these fungi in the field, but first its behaviour in natural soils must be studied.     

Possibilités et limites de la monoculture en relation avec l'application de diverses mesures culturales1

La monoculture du blé d'automne entraîn des baisses de rendement qui ne semblent pas dues uniquement à des causes sanitaires. Ces diminutions de rendement peuvent être atténuées par l'application de différentes mesures culturales. Un renforcement de la fumure azotée et, dans les parcelles exposées au piétin-verse, un traitement au bénomyl au début de la montaison, constituent les mesures les plus efficaces. Les effets négatifs de la monoculture ont été plus marqués aprés labour qu'en semis direct.     

Erwinia carotovora (Jones) Bergey et al. var. atroseptica (Hellmers et Dowson) Dye. Seed Tuber Infection Versus Symptom Expression in the Field1

Based on the time that symptoms of blackleg become evident in the field and the various ways of inoculation, it is concluded that the spread of symptom expression is due to the depth at which the bacteria penetrate into the interior of the tubers. Moreover, it is demonstrated that it is not the closed lenticels which prevent penetration, but the absence of a waterfilm in the intercellular spaces of the tuber tissue.