title: Purification and characterization of a carboxylesterase associated with organophosphate resistance in the greenbug, Schizaphis graminum (Homoptera: Aphididae).
abstract: The Type II esterase associated with organophosphate resistance in the greenbug, Schizaphis graminum, was purified by column chromatography and preparative electrophoresis resulting in over 100-fold purification and approximately 11% recovery. The native enzyme appears to exist as a heterodimer with the subunits equal to 52 and 56 kDa. The mass of the native enzyme was estimated at 102 kDa by gel filtration chromatography and the isoelectric focusing point was 4.8. The enzyme was inhibited by both paraoxon and mercuric chloride, suggesting that it is a serine hydrolase, although it was not inhibited by carbamate insecticides or eserine. The enzyme was active toward both beta- and alpha-naphthol esters, although the length of the side chain (C-2 or C-4) also affected activity. The enzyme displayed no activity toward acetylthiocholine. N-Terminal amino acid sequence analysis of the enzyme subunits indicates that residues Val-4 and Gly-10 of the larger fragment were highly conserved among 11 other carboxylesterase sequences. Sequence data from the smaller fragment did not reveal any similarity with other esterase sequences.
authors.affiliation: Department of Entomology, University of Nebraska, Lincoln 68583-0816, USA.
authors.forename: B D
authors.initials: BD
authors.lastname: Siegfried
authors.forename: M
authors.initials: M
authors.lastname: Ono
authors.forename: J J
authors.initials: JJ
authors.lastname: Swanson
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001042:Aphids / Q000187:drug effects* / Q000201:enzymology* / Q000235:genetics; D002265:Carboxylic Ester Hydrolases / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D019281:Dimerization; D007305:Insecticide Resistance; D007306:Insecticides / Q000494:pharmacology*; D007526:Isoelectric Point; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009943:Organophosphorus Compounds; D017386:Sequence Homology, Amino Acid
chemical_list: D007306:Insecticides; D009943:Organophosphorus Compounds; D002265:Carboxylic Ester Hydrolases