W. Liu et al., SUBSTRATE-SPECIFICITY AND INHIBITOR SENSITIVITY OF CHOLINESTERASES INHOMOGENATES OF WESTERN FLOWER THRIPS, Pesticide biochemistry and physiology, 49(2), 1994, pp. 121-131
Acetylcholinesterase (AChE) activity in homogenates of KCM strain west
ern flower thrips, Frankliniella occidentalis (Pergande), was chiefly
membrane bound, sensitive to eserine, and insensitive to diisopropyl p
hosphorofluoridate (DFP). The rate of substrate hydrolysis decreased i
n the order acetylthiocholine (ASCh)--> propionylthiocholine--> acetyl
-beta-methylthiocholine (MeSCh)--> butyrylthiocholine (BuSCh). Inhibit
ion by excess substrate was not observed at concentrations up to 8.0 m
M. Inhibition by BW 284C51 indicated the presence of two components wi
th different sensitivity to this compound. Butyrylcholinesterase (BuCh
E) activity, which was considerably higher than AChE activity, was chi
efly soluble and sensitive to eserine and DFP and insensitive to BW 28
4C51. The sulfhydryl reagents p-hydroxymercuribenzoic acid and 5,5'dit
hiobis-2-nitrobenzoic acid inhibited AChE and BuChE activities. Severa
l organophosphates and carbamates were potent inhibitors of ASCh and B
uSCh hydrolysis with the organophosphates being especially active agai
nst BuSCh. Substrate specificity and inhibitor sensitivity of AChE and
BuChE from UMC strain thrips were similar but not identical to that o
f KCM thrips. It was suggested that BuChE in western flower thrips mig
ht function as a scavenger enzyme to protect AChE from anticholinester
ase insecticides. Similarities between the properties of western flowe
r thrips cholinesterases and those reported previously for aphids were
striking. (C) 1994 Academic Press, Inc.