According to the current model of nerve propagation, the function of acetylcholinesterase (AChE) is to terminate synaptic transmission of nerve signals by hydrolyzing the neurotransmitter acetylcholine (ACh) in the synaptic cleft to acetic acid (acetate) and choline. However, extra-synaptic roles, which are known as 'non-classical' roles, have not been fully elucidated. Here, we measured AChE activity with the enzyme bound to lipid membranes of varying area per enzyme in vitro using the Ellman assay. We found that the activity was not affected by density fluctuations in a supported lipid bilayer (SLB) induced by standing surface acoustic waves. Nevertheless, we found twice as high activity in the presence of small unilamellar vesicles (SUV) compared to lipid-free samples. We also showed that the increase in activity scaled with the available membrane area per enzyme.
Keywords: Ellman assay; acetylcholinesterase; enzyme activity; lipid membrane; surface acoustic waves.