title: Purification and characterization of a carboxylesterase involved in malathion-specific resistance from Tribolium castaneum (Coleoptera: Tenebrionidae).
abstract: Specific resistance to malathion in a strain of Tribolium castaneum is due to a 44-fold increase in malathion carboxylesterase (MCE) activity relative to a susceptible strain, whereas non-specific esterase levels are slightly lower. Unlike the overproduced esterase of some mosquito and aphid species, MCE in Tribolium castaneum accounts for only a small fraction (0.033-0.045%) of the total extractable protein respectively in resistant and susceptible strains. The enzyme was purified to apparent homogeneity from these two strains and has a similar molecular weight of 62,000. However, preparative isoelectricfocusing indicated that resistant insects possess one MCE with pI of 7.3, while susceptible insects possess a MCE with a pI of 6.6. Purified MCE from both populations had different K(m) and V(m) values for hydrolysis of malathion as well as for alpha-naphthyl acetate. The kinetic analysis suggests that MCE of resistant insects hydrolyses malathion faster than the purified carboxylesterase from susceptible beetles and that this enzyme has greater affinity for malathion than for naphthyl esters. Malathion-specific resistance is due to the presence of a qualitatively different esterase in the resistant strain.
authors.affiliation: Department of Pure and Applied Zoology, Gembloux Agricultural University, B-5030 Gembloux, Belgium.
authors.forename: Eric
authors.initials: E
authors.lastname: Haubruge
authors.forename: Marcel
authors.initials: M
authors.lastname: Amichot
authors.forename: André
authors.initials: A
authors.lastname: Cuany
authors.forename: Jean-Baptiste
authors.initials: JB
authors.lastname: Berge
authors.forename: Ludovic
authors.initials: L
authors.lastname: Arnaud
mesh_terms: D000818:Animals; D043182:Carboxylesterase; D002265:Carboxylic Ester Hydrolases / Q000302:isolation & purification / Q000378:metabolism*; D007305:Insecticide Resistance; D007306:Insecticides / Q000494:pharmacology*; D007525:Isoelectric Focusing; D007700:Kinetics; D008294:Malathion / Q000494:pharmacology*; D008970:Molecular Weight; D013347:Subcellular Fractions; D014231:Tribolium / Q000201:enzymology*
chemical_list: D007306:Insecticides; D002265:Carboxylic Ester Hydrolases; D043182:Carboxylesterase; D008294:Malathion