A recombinant insecticide-resistant mosquito carboxylesterase B1 was purified to homogeneity from an Escherichia coli expression system. After non-denaturing electrophoresis, active carboxylesterase B1 bands were identified using fast blue RR. Lineweaver-Burk plots of the crude and purified CaE B1 indicate that this enzyme obeys Michaelis-Menten kinetics with K-m value for mallathion of 39.3 and 67.4 mM. The V. of purified enzyme is approximately 17-folds of the value determined in crude homogenate. Carboxylesterase B1 detoxification of parathion had a major limitation which is the 1:1 stoichiometry. To improve the effectiveness of enzymatic detoxification, we developed an approach in which the catalytic activity of organophosphorus compound-inhibited carboxylesterase B 1 was restored by having sufficient amounts diacetylmonoxime. It was demonstrated that repeated addition of 25 times the molar concentration of parathion to carboxylesterase B1 in the presence of 4 mM diacetylmonoxime every 2h did not result in significant inhibition of the enzyme. Consequently the stoichiometry of enzyme detoxification is higher than 64: 1 for parathion. (c) 2004 Elsevier Inc. All rights reserved.