MS Assay Development for Acetylcholinesterase

In the following example we describe the implementation of a mass spectromet-ric assay for acetylcholinesterase (AChE) [22]. AChE plays an important role in the nervous system. This enzyme rapidly hydrolyzes the active neurotransmitter acetylcholine into the inactive compounds choline and acetic acid. Amongst others, low levels of acetylcholine in the synaptic cleft are associated with Alzheimer s disease [23, 24]. Patients afflicted by this disease may benefit from inhibition of AChE activity thereby increasing ACh level. 

Traditionally, plants are a rich source of AChE inhibitors. People from the Caucasus used bulbs of snowdrops Galanthus sp.) to treat forgetfulness [25]. The active compound in this plant has been isolated and called galanthamine. Other plant-derived AChE inhibitors used for treatment of Alzheimer s disease include Huperzine A from Huperzia serrata and Rivastigmine (Excelon). The latter is a derivative from physostigmine isolated from the calabar bean, Physos-tigma vmmosum. 

Upon starting the AChE pump, a ready decrease in the substrate and a matching increase in the product trace was observed. Injections of galanthamine resulted in a negative peak in the product trace and a positive peak in the substrate trace, accurately matching the peaks observed in the galanthamine trace. 

As AMQI was both an expensive and unstable artificial substrate, it was replaced by the native substrate of AChE, acetylcholine that is both cheap and 

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