Abstract
The activities of carboxylesterases (CaE, EC 3.1.1.1) from laboratory cultured susceptible and malathion-resistantCulex quinquefasciatuswere estimated, and esterase bands were identified by electrophores. Total CaE activity in malathion-resistant larvae increased significantly with different CaE substrates, i.e., naphthyl acetate, naphthyl propionate, and naphthyl butyrate. Michaelis constant (Km) values of CaE for different naphthyl ester substrates showed that naphthyl propionate and butyrate are more specific substrates for CaE than naphthyl acetate. Arrhenius temperature plots showed decreased breakpoints for CaE from the malathion-resistant larvae with all three naphthyl ester substrates studied. Polyacrylamide gel electrophoresis of partially purified CaE revealed a less intense esterase band (B2) in the resistant larvae when the eletrophoretograms were stained with naphthyl butyrate. The possible use of these results for detection of insecticide resistance in mosquitoes is discussed.
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