Possible difference in the structure of acetylcholinesterase between insecticide susceptible and resistant strains of Culex tritaeniorhynchus resulted from structure-activity relationship of 3-alkylsulfonylphenyl methanesulfonates

Abstract

Acetylcholinesterase (AChE) inhibiting activity of eight 3-alkylsulfonylphenyl methanesulfonates was measured and its relationship with the structure of substituted alkyl moieties was analyzed in susceptible and resistant strains of Culex tritaeniorhynchus. The activity of the compounds was not so potent as that for the green rice leafhopper, Nephotettix cincticeps, previously reported. However, a parabolic relationship of the activity was detected with the distance between the S atom and the distal C atom of the alkyl moiety. The shape of the parabolic curve and the optimum distance were the same in susceptible and resistant strains, but the activity was about 100 times higher for AChE of the susceptible strain than for that of the resistant strain. No significant relationship was detected with the steric constant. An activity structure relationship was, however, detected with the steric constant in N. cincticeps, but not with the distance S-C, based on the previous results. Considering that the sulfone moiety of methanesulfonates conjugates with the esteratic subsite of the AChE active site to inhibit its activity, a structural change apparently occurred in the esteratic subsite of AChE in the resistant strain of C. tritaeniorhynchus, and was different from that of N. cincticeps.