ENZYMATIC DETERMINATION OF FENITROTHION BY CHOLINESTERASE AND ACETYLCHOLINESTERASE ON FLUOROGENIC SUBSTRATES

The action of the enzymes acetylcholinesterase and cholinesterase on t he substrates indoxyl-acetate and 2-naphthyl acetate was studied kinet ically. Both enzymes convert the substrates to highly fluorescent prod ucts (3-hydroxy-indole and 2-naphthol, respectively). The kinetic curv es present the initial rate as the variation of fluorescence for a uni ty of time (Delta F/Delta t) against the substrate concentration. This enzymatic reaction was investigated in presence of the inhibitor orga nophosphate pesticide fenitrothion. From the kinetic curves the enzyma tic parameters and enzyme and substrate concentrations used for the ca libration curve can be obtained. Four simple spectrofluorimetric metho ds for the enzymatic determination of fenitrothion were developed show ing detection limits between 5.5 to 19.5 mu mol/l, depending on the en zyme and the substrate used. The precisions (R.S.D.) of the methods we re between 1.6 and 9.6%. A comparative study of the kinetic enzymatic parameters and the detection limits was performed. A good correlation was obtained between inhibition constants and the detection limit.