An ultrasensitive electrometric system to measure membrane-bound acetylcholinesterase activity

A very sensitive method for the determination of membrane-bound acetylcholinesterase from sarcoplasmic reticulum is described. The acetic acid which is released by the enzymatic hydrolysis of acetylcholine is measured by means of an electrometric system. Diluted hydrochloric acid is used as the standard to evaluate the amount of H+ produced during the time course of the reaction. With the use of a bucking voltage device the sensitivity of the method permits one to follow changes in H+ concentration below 1 microM. Therefore the enzyme activity can be estimated using a very small amount of sarcoplasmic reticulum protein. This procedure is very simple, accurate and reproducible, and it can be applied to measure membrane-bound acetylcholinesterase where the membrane suspension makes it difficult to employ spectrophotometric techniques.