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(W/EH118) Daphnia magna cytochrome P-450 related enzymes as a potential biomarker of organophosphates exposure. Tonkopii, Valerii1, Zagrebin, Anatoly1, 1 ABSTRACT- Daphnia magna cytochrome P-450 related enzymes as a potential biomarker of organophosphates exposure. Tonkopii V.D. and A.Zagrebin, Department of Ecotoxicology, Institute for Lake Research, Russian Academy of Sciences, St.Petersburg, Russia. It is well known that for many types of vertebrates several enzymes participate in the metabolism of OP. They include OP hydrolyzing enzymes, such as CYP type of monooxygenases (MOs), arylesterases (ArE), and carboxylesterases (CaE). The participation of these enzymes in the metabolism of OP to Daphnia magna is unknown. The effect of some inducers (phenobarbital, a-naphthoflavone, 3-methylcholantrene) and inhibitors (piperonyl butoxide, SKF-525a) on OP hydrolyzing enzymes activity and toxicity of OP was studied. Two groups of OP were used: those not requiring metabolic activation before expressing their toxicity (dichlorvos, paraoxon, mevinphos, chlorfenvinphos) and those requiring metabolic activation (parathion, malathion, diazinon, fenthion). The toxicity of OP was determined with the value of average lethal concentration ( LC50 ). The activity of enzymes in daphnias whole organism homogenates or microsomes was investigated. The MOs activities were measured fluorometrically with two substrates, 7-pentoxyresorufin and 7-ethoxyresorufin. CaE activity was measured using a spectrophotometric assay, and the ArE activity was determined spectrophotometrically by measuring the formation of 4-nitrophenol from substrate paraoxon. Exposure of daphnids with inducers has been shown to markedly increased the activity of all investigated OP hydrolyzing enzymes. Enzyme inducers increased the acute toxicity of metabolically activated OP and decreased the toxicity of OP not requiring metabolic activation. The decrease in ArE and MOs activities was observed following exposure of SKF-525a and piperonyl butoxide. These inhibitors with contrast to inducers reduced the toxicity of metabolically activated OP and did not affect the toxicity OP without metabolitic activation. These different CYP related enzymes activities may serve not only as biomarker of OP exposure but also as predictors of toxicants effects. Key words: Daphnia magna, biomarker, cytochrome P-450, organophosphorus pesticides |
