Yerushalmi, N., & Cohen, E. 2002 Acetylcholinesterase of the California red scale Aonidiella aurantii Mask.: Catalysis, inhibition, and reactivation.. Pesticide Biochemistry and Physiology 72(3): 133-141.

Notes: The properties of the California red scale, Aonidiella aurantii, acetylcholinesterase (AChE) were studied using various substrates, inhibitors, and reactivators. The enzyme is inhibited by di(p-allyl-N-methylaminophenyl)pentane-3-one, is insensitive to tetraisopropyl pyrophospho amid ate, and displays the substrate inhibition phenomenon. The insect AChE deviates from its vertebrate counterparts by requiring a comparatively higher level of substrate to attain inhibition, by effectively hydrolyzing the larger homologous substrate propionyl thiocholine, by having a very high sensitivity to a bulkier inhibitor such as chlopyrifosoxon, by having insensitivity to the peripheral anionic site (PAS) inhibitor fasciculin, and by being reactivated by pyridine-2-aldoxime methyl iodide but not by 1-(4-aminocarbonylpyridinium-1'-(2'-pyridiniumaldoxime)dimethyl dibromide. Those differences were discussed as being associated with probable changes of amino acid composition within the enzyme acyl pocket and the PAS. Based on the above comparison, the insect enzyme may be regarded as an intermediate between AChE and butyrylcholinesterase. Among the organophosphorus (OP) compounds, chlopyrifos-oxon and 7-(methylethoxyphosphinyloxy)-1-methyl quinolinium were the most powerful inhibitors, while paraoxon was two orders of magnitude less effective. Among the carbamates, carbaryl was similar to paraoxon in its inhibitory effects followed by aldicarb and pirimicarb. The alkaloid huperzine A is an extremely potent inhibitor of the diaspidid AChE (with a K-i value in the subnanomolar range). The quaternary ammonium ligands propidium, edrophonium, and d-tubocurarine displayed high levels of inhibition. Toxogonin was the most powerful reactivator of OP-inhibited enzyme, while its nonoxime analog 1,1-bis(4-tertbutylpyridinium)dimethylether dichloride was without effect. Possible reasons for the enhanced inhibition of AChE in the presence of carbaryl and Toxogonin were discussed.