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Mechanism of action of acetylcholinesterase inhibitors

The top row shows the normal situation. In the left panel, the nitrogen of acetylcholine is attracted to the anionic site of the acetylcholinesterase enzyme through electrostatic attraction, while an oxygen atom of the carboxyl group links to a hydroxyl group of a serine moiety at the "esteric" or "esteratic" site. Hydrolysis is catalyzed at the esteric site to form choline and acetic acid. The middle row shows the action of a reversible inhibitor of acetylcholinesterase (neostigmine). Reversible cholinesterase inhibitors form a transition state complex with the enzyme, just as acetylcholine does. These compounds are in competition with acetylcholine in binding with the active sites of the enzyme. The bottom row shows the action of an irreversible inhibitor of acetylcholinesterase (the quasi-irreversible organophosphate diisopropyl fluorophosphate, an organophosphorus insecticide). (Illustration by Sbolmer on February 26, 2012. Creative Commons Attribution-Share Alike 3.0 Unported License, Text by Dr. Douglas J Lanska.)