Metabolism, pesticides

Table 15.2 Oxidation reactions in microbial pesticide metabolism (Bollag and Liu 1990)...

Because of the Importance of GSH conjugation In pesticide metabolism and the diversity of the plant kingdom. It seemed desirable to study the catabolism of another GSH conjugate In several plant species. Pentachloronltrobenzene-UL- C,... 

The methyl transferase reaction was demonstrated with penta-chlorothiophenol and a number of other substrates. The importance of this reaction in pesticide metabolism needs further evaluation. Some conversion of pentachlorothioanisole to pentachlorothioanisole sulfoxide was observed vivo, but this reaction was not specifically Investigated. 

Evidence was also provided that Insoluble residues may be produced from GSH conjugates via cysteine conjugate or thiol Intermediates. These studies also suggested that certain reactions should be studied in greater detail to assess their importance in pesticide metabolism l.e., the C-S lyase reaction, the methyl transferase reaction, and the transamination reaction. 

Shimabukuro, R. H. Lamoureux, G. L. Frear, D. S. Pesticide Metabolism in Plants Reactions and Mechanisms, Proceedings of the US-India Seminar on Biodegradable Pesticides, April 16-19, 1979, Lucknow, India. 

In both these cases where an Insect cytochrome P-A50 system has been shown to be responsible for the oxidation of a-plnene and pulegone, the enzyme had to be Induced to higher activity to effectively catalyse the reaction. This leads to the question of whether Insect P-A50-dependent oxidations are sufficiently active In natural situations to produce a significant amount of the metabolites. Due to the Importance of cytochrome P-A50 oxidations In pesticide metabolism, there are, fortunately, several studies which show that the Insect oxidase system Is easily and rapidly Induced In response to a large variety of non-nutrient chemicals In the food. 

Modern High-Performance Liquid Chromatography in Pesticide Metabolism Studies... 

This paper is the only one in the liquid chromatography portion of this symposium which will attempt to deal with chromatography specifically from the viewpoint of the pesticide metabolism chemist. A residue analyst knows what compound he must analyze for, and develops his method with the properties of that substance in mind. On the other hand, the pesticide metabolism chemist has a different problem. At the conclusion of the treatment, exposure, and harvest phases of a radiolabeled metabolism study, he divides his material into appropriate samples, and extracts each sample with selected solvents to obtain the radioactive materials in soluble form. Typically these extracts consist of low levels (ppm) of carbon-14 labeled metabolites in a complicated mixture of normal natural products from the plant, animal, or soil source. The identity of each metabolite is unknown, and each must be isolated from the natural background and from other labeled metabolites in sufficient quantity and in adequate purity for identification studies, usually by mass spectrometry. The situation is rather like looking for the proverbial "needle in the haystack" when one does not know the size, shape,or composition of the needle, or even how many needles there are in the stack. At this point a separation technique must be selected with certain important requirements in mind. 

It is not my purpose to expound chromatographic theory, or to discuss the fine points of column preparation, solvent selection, or new advances in detectors. The papers that follow deal with recent developments in these areas, and what they report is as applicable to pesticide metabolism analyses as to residue analyses. Instead, I shall describe a working radiochromatograph for the pesticide research laboratory and discuss some of the problems associated with this type of instrument. 

I shall close by describing some of the possibilities and procedures open to the analyst in the study of pesticide metabolism problems. 

Hodgson, E., and Philpot, R. M. Interaction of methylenedioxyphenyl (1,3-benzodioxole) compounds with enzymes and their effects on mammals. Drug Metab. Rev. 3, 231,1974. Hodgson, E. Induction and inhibition of pesticide-metabolizing enzymes Roles in synergism of pesticides and pesticide action. Toxicol. Ind. Health 15, 6,1999. 

Cooper et al. [86] analyzed environmental matrices derived from soil, plant, and animal extracts to study an insecticide, a fungicide, and their metabolites. The clean-up steps consisted simply of removal of the solid debris by centrifugation and filtration. The authors recognized that while retention time reproducibility was satisfactory for a study of pesticides metabolism, in order to achieve the sensitivity required for this type of analysis a sample preconcentration step was required before the CEC separation. 

Among the reactions performed by the cytochrome P450 monooxygenase system, epox-idation, hydroxylation, N-dealkylation, O-dealkylation, desulfuration, and sulfoxidation are the most important with respect to pesticide metabolism ... 

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