Properties and inhibition of acetylcholinesterase in resistant and susceptible German cockroaches (Blattella germanica L.)

Acetylcholinesterase (AChE) from German cockroaches was partially characterized and examined for its possible involvement in resistance to organophosphate and carbamate insecticides in four resistant strains. Solubilized preparations from heads of susceptible cockroaches displayed optimal activity near pH 7.6, and activity increased linearly with increasing temperature up to 40°C. The kinetic parameters K_m and V_max, determined with acetylthiocholine iodide as substrate, were 1.03 × 10^-4M and 537 nmol/(min mg protein), respectively, for the susceptible strain. Differential centrifugation of both solubilized and nonsolubilized head homogenates indicates that over 90% of AChE activity is membrane associated, but that homogenization in the presence of detergent increases solubility. These conclusions are supported by nondenaturing gel electrophoresis which suggests that mobility and resolution of different molecular forms was dependent on solubilization. The biomolecular rate constants, k_i, in four stains of German cockroaches which display varying levels of organophosphate and carbamate resistance were similar to the susceptible strain for chlorpyrifos oxon, malaoxon, and propoxur, suggesting that insensitivity of AChE in German cockroaches is probably not a common factor conferring resistance to these compounds.