How Sarin Works
Sarin is a nerve agent, which means it interferes with the normal signaling between nerve cells. It acts in much the same way as organophosphate insecticides, block nerve endings from allowing muscles to stop contracting. Death may occur when the muscles controlling breathing become ineffective, causing asphyxiation.
Sarin acts by inhibiting the enzyme acetylcholinesterase. Ordinarily, this proteins degrades acetylcholine released at the synaptic cleft. The acetylcholine activates nerve fibers that cause muscles to contract. If the neurotransmitter is not removed, the muscles don't relax. Sarin forms a covalent bond with the serine residue at the active site on the cholinesterase molecule, making it unable to bind to acetylcholine.