Study of the mechanism ofFlavobacteriumsp. for hydrolyzing organophosphate pesticides

The biotransformation by Flavobacterium sp. of the following organophosphate pesticides was experimentally and theoretically studied: phorate, tetrachlorvinphos, methyl-parathion, terbufos, trichloronate, ethoprophos, phosphamidon, fenitrothion, dimethoate and DEF. The Flavobacterium sp. ATCC 27551 strain bearing the organophosphate-degradation gene was used. Bacteria were incubated in the presence of each pesticide for a duration of 7 days. Parent pesticides were identified and quantified by means of a gas-chromatography mass spectrum system. Activity was considered as the amount (micromol) of each pesticide degraded by Flavobacterium sp. Also, structural parameters obtained by means of the CAChe program package for biomolecules, the reactivity index of phosphorus, of oxygen at the P = O function and of sulfur at the P = S function, and lipophilicity (log Poct) (ALOGPS v. 2.0) were obtained for each pesticide. Pesticides were hydrolyzed at the bond between phosphorous and the heteroatom, producing phosphoric acid and three metabolites. Enzymatic activity was significantly explained by the following multiple linear relationship: Enzymatic activity = 162.2 - 9.5(dihedral angle energy) - 25.0(Total energy) - 0.51(Molecular weight). Finally, a mechanism of Flavobacterium sp. to hydrolyze pesticides was proposed.

A new in vitro method for testing plant metabolism in mutagenicity studies

A rapid method was proposed to detect whether a harmless agricultural chemical can be converted into a mutagenic one by plant metabolism. The method is based on the use of Nicotiana alata cell cultures. Results obtained with five pesticides (atrazine, dichlorvos, tetrachlorvinphos, Kelevan, and maleic hydrazide) suggest that the proposed method simulates the metabolism of the whole plant. This procedure was also successfully applied to the genetic system of Aspergillus nidulans. One pesticide, atrazine, induced mutations and somatic segregation only after metabolism during cocultivation with N. alata cells.

Metabolic demethylation of the insecticide dimethylvinphos in rats, in dogs, and in vitro

1. The alkenyl phosphate insecticide, dimethylvinphos, is rapidly metabolized and eliminated by rats and dogs. 2. Metabolism proceeds via demethylation followed by the hydrolysis of desmethyl dimethylvinphos to 2,4-dichlorophenacyl chloride which is further metabolized mainly to 2,4-dichloromandelic acid, 1-(2,4-dichlorophenyl)ethanol (glucuronide) and 2,4-dichlorphenylethanediol (glucuronide). 3. The dechlorination of 2,4-dichlorophenacyl chloride to 2,4-dichloroacetophenone proceeds via the spontaneous formation of S-(2,4-dichlorophenacyl) glutathione which is converted to the ketone by an enzyme-catalysed glutathione-dependent reaction. 4. Demethylation of dimethylvinphos occurs in liver fractions via the action of two enzymes: glutathione S-methyl transferase in the cytosol, and microsomal mono-oxygenase. The relatively high activities of both enzymes in dog liver (compared with rat liver) partly account for the observed differences in metabolism and toxicity of dimethylvinphos in the two species. 5. The glutathione transferase is enhanced twofold by pre-treatment of rats with 0-1% phenobarbital in their drinking water. This treatment also induces the microsomal demethylation 45-fold and results in a greater than 13-fold protective effect against the acute toxic effects of dimethylvinphos.