Kinetic behaviour of acetylcholinesterase from muscle microsomal membranes

In order to determine whether catalytic hydrolysis of acetylcholine, observed in muscle microsomes enriched in sarcoplasmic reticulum membranes, was carried out by true acetylcholinesterase we studied the substrate specificity of this enzyme, its kinetic behaviour and its sensitivity against several reversible inhibitors. The results showed that the enzyme from muscle microsomes had acetylcholine (or acetylthiocholine) as the preferent substrate and was also able to hydrolyze acetyl-beta-methylcholine. The enzyme had a Km of 100-120 microM, being inhibited by a high substrate concentration. Acetylcholinesterase in this source was competitively inhibited by BW-284-c-51, eserine and decamethonium with ki values of 0.025 microM, 0.021 microM and 65 microM, respectively. The enzyme was poorly inhibited by the pseudocholinesterase inhibitor ethopropazine. The results show that the hydrolytic enzyme is indeed acetylcholinesterase.