A Penicillium lilacinum BP303 was found to be able to degrade various organophosphorus pesticides by cleaving P-O in the phosphotriesters bond and P-S linkage in the phosphothiolesters effectively. The novel fungal enzyme hydrolyzing methyl parathion, parathion, paraoxon, coumaphos, demeton-S, phosmet, and malathion has been purified to homogeneity and characterized. It is a monomeric structure with a molecular mass of 60,000 Da, a pI of 4.8, and the enzyme activity was optimal at 45 degreesC and pH 7.5, The activities were strongly inhibited by Hg2+, Fe3+, rho-chloromercuribenzoate, iodoacetic acid, and N-ethylmaleimide, while Cu2+, beta-mercaptoethanol, dithiothreitol, dithioerythritol, glutathione, and detergents slightly activated the enzyme. As judged by catalytic efficiencies, paraoxon is the preferred substrate. (C) 2003 Elsevier Inc. All rights reserved.