BIOCHEMICAL CHARACTERIZATION AND PURIFICATION OF ESTERASES FROM THREE STRAINS OF GERMAN COCKROACH, BLATTELLA GERMANICA (DICTYOPTERA : BLATTELLIDAE)

Three strains of German cockroach, Blattella germanica (L.) showed varying levels of resistance to chlorpyrifos, methyl parathion, propoxur, bendiocarb, and cypermethrin. The general esterase activity was at least twofold higher than susceptible strain. The subcellular distribution studies revealed that the majority of the esterase activity is present in the 100,000g cytosolic fraction. Only a small portion of the activity was membrane bound. Using non-denaturing gel electrophoresis, ten isozymes were identified in German cockroaches. These isozymes were isolated individually from the gels and analyzed for differences in activity. The isozymes E5, E6, and E7 of resistant strains had significantly higher specific activities when compared with the susceptible strain. The purification process using various column chromatography and preparative gel electrophoresis resulted in 9–11% of total esterase recovery. About double the amount of E6 was recovered from the resistant strains when compared with the susceptible strain. Kinetic analyses of E6 did not indicate differences in Km and Vmax values between the resistant and susceptible strains. Also, inhibition of esterase activity by paraoxon, chlorpyrifos, and propoxur did not suggest any structural differences in esterase E6 between strains. The results suggest that the increased production of E6 esterase contributes to insecticide resistance in German cockroaches. The role of E6 may be sequestration of toxic molecules rather than hydrolysis. © 1996 Wiley-Liss, Inc.