| Abstract
| - An acetylcholinesterase (AChE, EC 3.1.1.7) was purified from the head of the insecticide susceptibleoriental fruit fly, Bactrocera dorsalis (Hendel), by affinity chromatography of Triton X-100 extract.The degree of purification was about 8183-fold with recoveries of 52%. The molecular mass of purifiedAChE was 116 kDa for its native protein (nonreduced form) and 61 kDa for its subunits (reducedform) as revealed on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS−PAGE),suggesting that the homodimer of AChE linked with disulfide bonds. Nondenaturing PAGE of thepurified AChE revealed only one molecular form. The maximum velocities (Vmax) for hydrolyzingacetylthiocholine (ATC), propionylthiocholine, and S-butyrylthiocholine were 833.3, 222.2, and 57.5μmol/min/mg, and the Michaelis constants (Km) were 87.9, 26.9, and 195.3 μM, respectively. Morethan 97% of AChE activity was inhibited by 10 μM eserine or BW284C51, but only 53% of the activitywas inhibited by ethopropazine at the same concentration. On the basis of the substrate and inhibitorspecificities, the purified enzyme appeared to be a true AChE. Nevertheless, the purified AChEexhibited some distinctive characteristics including (i) a lack of the substrate inhibition phenomenonwhen using ATC as the hydrolyzing substrate and (ii) a higher Vm value for ATC than AChE fromother insect species. These biochemical properties may show that AChE purified from the orientalfruit fly may have structural differences from those of other insect species. Keywords: Acetylcholinesterase; kinetics; purification
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