Catalyzes the reversible synthesis of acetylcholine (ACh) from acetyl CoA and choline at cholinergic synapses. acetyl-CoA + choline = acetylcholine + CoA The 54 kDa and 13 kDa chains exist as a heterodimer. The N-terminus of choline O-acetyltransferase 67 kDa and 54 kDa chains are blocked. Belongs to the carnitine/choline acetyltransferase family.