Other drugs on the market, approved to treat mild to moderate Alzheimer's, are believed to work by inhibiting cholinesterase, an enzyme that breaks down acetylcholine which is a chemical used by nerves to communicate with each other.
Acetylcholine is not an enzyme
Acetylcholine is a chemical not an enzyme. 
( z1 enzyme :polarity - :domain ( z2 amino-acid :name ( z3 name :op "Acetylcholine" ) ) )