BIOCHEMICAL-CHARACTERIZATION AND PURIFICATION OF ESTERASES FROM 3 STRAINS OF GERMAN-COCKROACH, BLATTELLA-GERMANICA (DICTYOPTERA, BLATTELLIDAE)

Three strains of German cockroach, Blattella germanica (L.) showed var ying levels of resistance to chlorpyrifos, methyl parathion, propoxur, bendiocarb, and cypermethrin. The general esterase activity was at le ast twofold higher than susceptible strain. The subcellular distributi on studies revealed that the majority of the esterase activity is pres ent in the 100,000g cytosolic fraction. Only a small portion of the ac tivity was membrane bound. Using non-denaturing gel electrophoresis, t en isozymes were identified in German cockroaches. These isozymes were isolated individually from the gels acid analyzed for differences in activity. The isozymes E5, E6, and E7 of resistant strains had signifi cantly higher specific activities when compared with the susceptible s train. The purification process using various column chromatography an d preparative gel electrophoresis resulted in 9-11% of total esterase recovery. About double the amount of E6 was recovered from the resista nt strains when compared with the susceptible strain. Kinetic analyses of E6 did not indicate differences in K-m and V-max values between th e resistant and susceptible strains. Also, inhibition of esterase acti vity by paraoxon, chlorpyrifos, and propoxur did not suggest any struc tural differences in esterase E6 between strains. The results suggest that the increased production of E6 esterase contributes to insecticid e resistance in German cockroaches. The role of E6 may be sequestratio n of toxic molecules rather than hydrolysis. (C) 1996 Wiley-Liss, Inc.