Insensitivity of acetylcholinesterase as a factor in resistance of houseflies to the organophosphate Rabon

Acetylcholinesterase from an organophosphate-resistant strain of housefly exhibited a decrease in sensitivity to Rabon in vitro, to the extent of 206-fold for the soluble enzyme and 38-fold for the particulate. These effects upon the bimolecular reaction constant, k_i, were due to a 573-fold decrease in affinity of the inhibitor for the soluble and 103-fold for the particulate enzyme, coupled with a small increase in reactivity.