Subcellular Distribution and Characterization of Esterase Isozymes from Insecticide-Resistant and -Susceptible Strains of German Cockroach (Dictyoptera: Blattellidae)

Esterases from insecticide-resistant and -susceptible strains of German cockroach, Blattella germanica (L.), were isolated and analyzed for differences in activity. The isozymes E5, E6, E7, and E8 of resistant strains indicated about two- to fivefold increases in activity compared with those of the susceptible strain. These isozymes constituted approximately 60% of the total activity in the resistant strains, whereas they contributed only about 40% activity in the susceptible strain. Subcellular distribution studies showed that most esterase activity is present in the 100,000 x g fraction of the homogenate (cytosolic). Only a small portion of activity was membrane bound. Molecular weights of the esterase isozymes calculated based on their retardation coefficients ranged between 48 and 81 kd.