Acetylcholinesterase, also known as AChE, is an enzyme which is critical to the function of animals from ants to elephants. This enzyme's sole responsibility is to break down the neurotransmitter acetylcholine. Acetylcholine sends messages between nerves, signaling muscle contractions. If the neurotransmitter was not broken down after it had served its function, the muscle involved would not be able to relax, and this could create spasms, paralysis, and other problems.