Enantioselective Interaction of Acid α‑Naphthyl Acetate Esterase with Chiral Organophosphorus Insecticides

Abstract

Many previous works have demonstrated that acetylcholinesterase (AChE) was enantioselectively inhibited by chiral organophosphorus insecticides (OPs) and that a significant difference in reactivation existed for AChE inactivated by (1<i>R</i>)- versus (1<i>S</i>,3<i>S</i>)-stereoisomers of isomalathion. It had been known that α-naphthyl acetate esterase (ANAE), an enzyme which might play an essential role in the growth of plants and the defense of plants against environmental stress by regulating the concentration of hormones in plants, can be inhibited by OPs. However, it was unknown whether interaction of ANAE with chiral OPs was enantioselective. The present work investigated the inhibition kinetics and spontaneous reactivation of ANAE inactivated by enantiomers of malaoxon, isomalathion, and methamidophos. The order of inhibition potency is (<i>R</i>) > (<i>S</i>) for malaoxon, (1<i>R</i>,3<i>R</i>) > (1<i>R</i>,3<i>S</i>) > (1<i>S</i>,3<i>R</i>) > (1<i>S</i>,3<i>S</i>) for isomalathion, and (<i>S</i>) > (<i>R</i>) for methamidophos according to bimolecular rate constants of inhibition (<i>k</i>_i), which is consistent with the order observed in the enantioselective inhibition of AChE by malaoxon, isomalathion, and methamidophos. The difference in spontaneous reactivation of AChE inactivated between (1<i>R</i>)- and (1<i>S</i>,3<i>S</i>)-isomers of isomalathion is conserved for ANAE. The observations indicated ANAE and AChE have similar selective inhibition kinetics and postinhibitory reactions in reaction with chiral OPs