ELECTROCHEMICAL TRANSDUCTION OF THE ACETYLCHOLINE ACETYLCHOLINESTERASE REACTION BY BILAYER-LIPID MEMBRANES

This work reports the transduction of the reaction of the enzyme acety lcholinesterase (AChE) with acetylcholine (ACh) as a model to demonstr ate how transient electrochemical signals from bilayer lipid membranes can be obtained by appropriate selection of the lipid composition of membranes. Membranes were prepared from mixtures of egg phosphatidyl c holine (PC) and dipalmitoyl phosphatidic acid (DPPA) for this purpose. Hydronium ions generated by the enzymatic reaction at the surface of BLMs caused a transient current due to a dynamic alteration of the ele ctrostatic fields at the surface of such membranes. The results were c onsistent with an electrostatic mechanism of perturbation of the surfa ce structure of the BLMs, where changes of local hydronium ion activit y which were associated with the enzymatic reaction altered the extent of ionization of the headgroups of the DPPA, thereby providing a tran sient charging current which lasted for a period on the order of secon ds. The delay time for observation of the transient was directly and r eproducibly related to the concentration of the substrate, which could be determined over a range of muM to mM levels. Investigation of the effects of solution pH, the presence of Ca2+ and the use of the enzyme inhibitor Neostigmine confirmed that the response was due to a genuin e selective chemical transduction process.