COMPARISON OF TWO METHODS FOR MEASURING PYRETHROID HYDROLYZING ESTERASES: EXTRACTION SELECTIVITY AND RADIOLABELED IDENTITY

Document Type : Original Article

Authors

1 Department of Plant Protection, College of Agriculture, Assiut University, Assiut, Egypt

2 NYSAES Department of Entomology, Geneva, N.Y. 14456

Abstract

Two published methods are used widely for measuring pyrethxoid hydrolyzing esterases. These two methods are based on measuring either the acid production (Jao and Casida, 1974) or the residual unhydrolyzed ester (Suzuki and Miyamoto, 1978). These methods were compared using (IRS, tirans), permethrin, labeled at the carbonyl carbon of the acid moiety, and rat liver microsomes. No consistent results were obtained and the enzyme activity determined by the first method was lower than that of the second one. The selectivity of the extract-ion procedure in method I and the identity of the labeled product were examined by TLC chromatography. Chloroform extract in acid production method contained more than 30% of the total acid released, thereby, introducing a large error in quantitation. Alkalinization of the reaction mixture prior to chloroform extraction using 1 ml buffer, pH 10, changed the extraction selectivity of acid permethrin (DCVA) in favour of the aqueous phase and consequently increased the accuracy of this method. No chemical hydrolysis of (IRS, trans) permethrin could be detected under conditions of pH 10 over 60 minute period.

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