Editing Nerve agent (section)

===Mechanism of action===
When a normally functioning [[motor nerve]] is stimulated, it releases the [[neurotransmitter]] [[acetylcholine]], which transmits the impulse to a muscle or organ. Once the impulse is sent, the enzyme [[acetylcholinesterase]] immediately breaks down the acetylcholine in order to allow the muscle or organ to relax.

Nerve agents disrupt the nervous system by inhibiting the function of the enzyme acetylcholinesterase by forming a [[covalent bond]] with its [[active site]], where acetylcholine would normally be broken down (undergo [[hydrolysis]]). Acetylcholine thus builds up and continues to act so that any nerve impulses are continually transmitted and muscle contractions do not stop. This same action also occurs at the gland and organ levels, resulting in uncontrolled drooling, tearing of the eyes (lacrimation) and excess production of mucus from the nose (rhinorrhea).

The reaction product of the most important nerve agents, including Soman, Sarin, Tabun and VX, with acetylcholinesterase were solved by the U.S. Army using [[X-ray crystallography]] in the 1990s.<ref name=pmid10353814>{{cite journal | vauthors = Millard CB, Kryger G, Ordentlich A, Greenblatt HM, Harel M, Raves ML, Segall Y, Barak D, Shafferman A, Silman I, Sussman JL | title = Crystal structures of aged phosphonylated acetylcholinesterase: nerve agent reaction products at the atomic level | journal = Biochemistry | volume = 38 | issue = 22 | pages = 7032–9 | date = June 1999 | pmid = 10353814 | doi = 10.1021/bi982678l }}</ref><ref name="Millard et al 1999">{{cite journal |doi=10.1021/ja992704i |title=Reaction Products of Acetylcholinesterase and VX Reveal a Mobile Histidine in the Catalytic Triad |journal=Journal of the American Chemical Society |volume=121 |issue=42 |pages=9883–4 |year=1999 |last1=Millard |first1=Charles B |last2=Koellner |first2=Gertraud |last3=Ordentlich |first3=Arie |last4=Shafferman |first4=Avigdor |last5=Silman |first5=Israel |last6=Sussman |first6=Joel L | name-list-style = vanc }}</ref> The reaction products have been confirmed subsequently using different sources of acetylcholinesterase and the closely related target enzyme, butyrylcholinesterase. The X-ray structures clarify important aspects of the reaction mechanism (e.g., stereochemical inversion) at atomic resolution and provide a key tool for antidote development.