A class of highly toxic compounds that act by affecting the action of acetylcholine, a neurotransmitter regulated by the enzyme acetylcholinesterase (AChE). The nerve agents, which are organophosphates, bind to AChE and block its action. Consequently there is nothing to stop the build up of acetylcholine, and exposure to small amounts of nerve gas can kill in minutes. There are two series of agents. The G-series was produced by German scientists in the 1930s and 40s (the G stands for German). The main ones are tabun (GA), sarin (GB), soman (GD), and cyclosarin (GF). A further series of nerve agents is the V-series. The most common of these is VX, which was discovered at Porton Down in the UK in 1952. Nerve agents are classified as weapons of mass destruction by the UN.