The active site and substrate bind to each other with ionic, van der Waal, and hydrogen bonding interaction. Ionic bonding is the rare, as water is seldom present near the active site. Mostly all the enzyme catalyzed reactions are carried out in hydrophobic environment.
The acetylcholine requires the serine amino acid to be present near the active site. Serine carries out a nucleophilic attack on the substrate. The acyl group is easily broken as compared to a peptide bond. The reaction is proceeds by a catalytic triad. The serine, histidine, and aspartic acid all help in the completion of the reaction.
The ester bond is easily hydrolyzed. If the environment is aqueous then the nucleophilic attack cannot take place properly. Esters are more reactive than amides, and their hydrolysis easier than the amides.