 Acetylcholinesterase

Acetylcholinesterase is an enzyme that hydrolyses the neurotransmitter acetylcholine to choline and acetate. Its activity helps terminate signalling at cholinergic synapses, including the neuromuscular junction. Chemically, it is a catalyst: the reaction consumes acetylcholine and water, while the enzyme can be reused.^[ref]

The distinction between removal of a messenger and inhibition of its receptor matters. Reducing acetylcholinesterase activity leaves more acetylcholine available to activate receptors; it does not directly substitute for the messenger or block every receptor. Thus the duration of a chemical signal depends both on its release and on its clearance. Measuring reaction-product accumulation in an enzyme assay tests the clearance machinery separately from a responding muscle or neuron.