Enzymological and inhibitory properties of acetylcholinesterase purified from Lygus hesperus knight (Hemiptera:Miridae)

• Published in: Insect biochemistry and molecular biology Vol. 22; no. 3; pp. 245 - 251
• Main Authors: Zhu, K.Y., Brindley, W.A.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 1992
• Subjects: Lygus hesperus; Miridae; acetylcholinesterase; inhibition; Lygus hesperus; kinetics, insecticide; purification; substrate specificity
• ISSN: 0965-1748; 1879-0240
• DOI: 10.1016/0965-1748(92)90061-I

We studied the enzymological and inhibitory properties of a 600-fold purified acetylcholinesterase (AChE, EC 3.1.1.7) from Lygus hesperus Knight. The optimal pH and temperature were 7.5–8.0 and 35–40°C, respectively, for hydrolyzing selected substrates. K m and V max were 6.9 × 10 −5 M and 42.9 units/mg for acetylthiocholine (ATC), 6.5 × 10 −5 M and 32.8 units/mg for acetyl-(β-methyl) thiocholine (AβMTC), 7.2 × 10 −5 M and 21.9 units/mg for propionylthiocholine (PTC), and 3.3 × 10 −3 M and 4.2 units/mg for S-butyrylthiocholine (BTC), at 37°C and pH 7.7. The efficiency for hydrolyzing different substrates was ATC > A βMTC > PTC > BTC. Enzyme activity was inhibited by 10 −7 M eserine or BW284C51, but not by ethopropazine. The enzyme's inhibitor and substrate specificities, and substrate (ATC) inhibition confirmed that it was an AChE. Bimolecular reaction constants were 9.44 × 10 5 M −1 min −1 for paraoxon, 2.21 × 10 5 M −1 min −1 for dichlorvos, 8.28 × 10 6 M −1 min −1 for naled, 2.15 × 10 4 M −1 min −1 for oxydemeton-methyl, 4.18 × 10 4 M −1 min − for demeton- S-methyl, for 2.98 × 10 5 M −1 min −1 for mevinphos, at 25°C. The inhibitory potency for all six organophosphorus compounds was mainly determined by the affinity between the organophosphates and AChE. Eserine and carbofuran were competitive inhibitors for the active sites of AChE. The competitive inhibition constant was 1.20 × 10 −8 M for eserine and 1.24 × 10 −8 M for carbofuran.