Zhu_1990_Pestic.Biochem.Physiol_36_22

Acetylcholinesterase (AChE) from Lygus hesperus Knight was partially characterized and examined to determine if insensitive AChE contributed to insecticide resistance in the field. The optimal pH and temperature were 8.5 and 35-40degC, respectively. The specific activity in head homogenates was higher than in thoracic or abdominal homogenates. AChE was likely to be a membrane-associated enzyme. The kinetic parameters, Km and Vmax, determined with acetylthiocholine iodide at 38degC, were 1.2 10-4 M and 43.4 nmol/min/mg protein, respectively, for the susceptible (S) population and 1.1 10-4 M and 45.3 nmol/min/mg protein, respectively, for the resistant (R) population. Neither parameter differed significantly between the two populations (P > 0.05). The bimolecular rate constant, ki, in the S and R populations was 2.8 105 and 8.3 103 M-1min-1, respectively, for paraoxon at 25degC, which indicates that AChE from the R population was about 34-fold less sensitive to paraoxon inhibition than AChE from the S population. AChE from the S population was homogenous to paraoxon inhibition, while AChE from the R population appeared to be heterogenous.