Acetylcholine is an ester of acetic acid and choline with chemical formulaCH3COOCH2CH2N+(CH3)3. This structure is reflected in the systematic name, 2-acetoxy-N,N,N-trimethylethanaminium. Proteins are composed of amino acids, because acetyl choline is a CHEMICAL COMPOUND and does not contain amino acids, it is not a protein. It is also classified as a neurotransmitter.