Acetylcholine is broken down by the enzyme Acetylcholinesterase (AChE). AChE belongs to the cholinergic family of enzymes that are involved in synthesizing, releasing, or altering acetylcholine. 

Acetylcholinesterase is found primarily at postsynaptic neuromuscular junctions, particularly in the muscles and nerves. It hydrolyzes and breaks down acetylcholine into acetate (acetic acid) and choline, which regulates acetylcholine levels and ensures that no excess remains in the synaptic cleft to cause the continued activation of receptors.