A microsomal esterase involved in cypermethrin resistance in the German cockroach, Blattella germanica

Adult male German cockroaches of the Marietta strain exhibited 5-fold resis tance to cypermethrin compared with the insecticide-susceptible Orlando str ain. The cypermethrin resistance level decreased to 2.9-fold when cockroach es were pretreated with S,S,S tributylphosphorotrithioate, indicating that esterases played a role in the resistance. Cypermethrin was metabolized fas ter 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 pu rification of microsomal esterases from the Marietta and Orlando strains wa s accomplished by anion exchange and hydrophobic interaction chromatography (HIC) and native-PAGE. HIC partitioned the single anion exchange peak of a -naphthyl acetate esterase activity into three fractions, HIC I, HIC II, an d HIC III. All three HIC fractions metabolized cypermethrin significantly f aster than microsomes. Native-PAGE analysis of each of these fractions reve aled a unique band in Marietta HIC II and III which was referred to as micr osomal esterase Marietta (MB.). MEmar was isolated by native-PAGE and found to hydrolyze a-naphthyl acetate at a rate of 25.5 mu mol/min/mg protein, r epresenting a purification of 54-fold over that of microsomes. Furthermore, Marietta strain HIC II and III fractions (which contained MEmar) metaboliz ed cypermethrin significantly faster than the corresponding fractions from the Orlando strain. MEmar metabolized cypermethrin at 3461 pmol/min/mg prot ein, representing a 225-fold increase over that of microsomes. MEmar was fo und to exhibit a molecular weight of 57 kDa by SDS-PAGE and 64 kDa by gel f iltration chromatography, indicating that the esterase was a monomer. Also, the MEmar isozyme was inhibited by paraoxon and phenylmethylsulfonyl fluor ide, indicating that the esterase was a "B"-type swine esterase. Finally, n one of the isozymes in the HIC III fraction, including the MEmar isozyme, b ound to concanavalin A, indicating that the HIC III isozymes were not glyco sylated.