Valles_2001_Pestic.Biochem.Physiol_71_56

Adult male German cockroaches of the Marietta strain exhibited 5-fold resistance to cypermethrin compared with the insecticide-susceptible Orlando strain. The cypermethrin resistance level decreased to 2.9-fold when cockroaches were pretreated with S,S,S-tributylphosphorotrithioate, indicating that esterases played a role in the resistance. Cypermethrin was metabolized faster by microsomal esterases from the Marietta strain (15.4 +/- 1.1 pmol/h/mg) than by those from the Orlando strain (12.5 +/- 0.2 pmol/h/mg). Partial purification of microsomal esterases from the Marietta and Orlando strains was accomplished by anion exchange and hydrophobic interaction chromatography (HIC) and native-PAGE. HIC partitioned the single anion exchange peak of alpha-naphthyl acetate esterase activity into three fractions, HIC I, HIC II, and HIC III. All three HIC fractions metabolized cypermethrin significantly faster than microsomes. Native-PAGE analysis of each of these fractions revealed a unique band in Marietta HIC II and III which was referred to as microsomal esterase Marietta (MEmar). MEmar was isolated by native-PAGE and found to hydrolyze alpha-naphthyl acetate at a rate of 25.5 umol/min/mg protein, representing a purification of 54-fold over that of microsomes. Furthermore, Marietta strain HIC II and III fractions (which contained MEmar) metabolized cypermethrin significantly faster than the corresponding fractions from the Orlando strain. MEmar metabolized cypermethrin at 3461 pmol/min/mg protein, representing a 225-fold increase over that of microsomes. MEmar was found to exhibit a molecular weight of 57 kDa by SDS-PAGE and 64 kDa by gel filtration chromatography, indicating that the esterase was a monomer. Also, the MEmar isozyme was inhibited by paraoxon and phenylmethylsulfonyl fluoride, indicating that the esterase was a -YB-type serine esterase. Finally, none of the isozymes in the HIC III fraction, including the MEmar isozyme, bound to concanavalin A, indicating that the HIC III isozymes were not glycosylated.