PURIFICATION AND CHARACTERIZATION OF AN ESTERASE ISOZYME FROM INSECTICIDE RESISTANT AND SUSCEPTIBLE STRAINS OF GERMAN-COCKROACH, BLATTELLA-GERMANICA (L)

The most active forms of esterases (E5, E6 and E7) from the German coc kroach, Blattella germanica (L.) were purified from resistant and susc eptible strains. About 45-155 fold purification with a 11-16% of total esterase recovery was achieved after different column chromatography and preparative gel electrophoresis. Elution profiles of resistant and susceptible strains were similar, but esterase E6 activity was higher in the resistant strains. Kinetic analyses indicate no differences in K-m values between the resistant and susceptible strains. However V-m ax was significantly higher in resistant strains. Inhibition of estera se activity by paraoxon, chlorpyrifos and propoxur did not suggest any structural differences in esterase E6 between strains. From these res ults we suggest that insecticide resistance in German cockroach is due to the increased production of E6 esterase. The role of E6 may be seq uestration of toxic molecules rather than hydrolysis.