ABSTRACT
Acetylcholinesterase (AChE) belongs to a distinct family of serine hydrolases and is found in both synaptic and nonsynaptic locations. At the synapses, it plays a major role in the hydrolysis of the neurotransmitter acetylcholine (ACh), while in nonsynaptic tissue its function is unclear. Snake venom, particularly from the family Elapidae, is a common nonsynaptic source of AChE. In the Elapidae, the genus Bungarus is well known as a prominent source, as it contains the highest levels of AChE detected in snake venoms (close to 8 mg/g of dried venom; 0.8% w/w). A review of the literature shows that no other tissues or biological uids exhibit such a high level of AChE activity. Comparative amino acid sequence studies have revealed that venom AChE exhibits signicant homology with the catalytic domain of cholinesterases from other sources but contains unique monomeric properties. Venom AChE from all species assayed has a similar sensitivity to different inhibitors, such as edrophonium, tacrine, propidium, BW284C51, and decamethonium; one exception is fasciculin, which varies in its inhibitory potency depending on the source of the venom AChE. From an evolutionary point of view, the enhanced complexity of venoms may provide a selective advantage to snakes. In this context, either the presence of large amounts of AChE or the presence of fasciculins is an important feature. In fact, the existence of elevated amounts of AChE or fasciculin in snake venom may be related to disruption of cholinergic transmission in the central nervous system and at the neuromuscular junction of the prey. Furthermore, the presence of AChE in snake venom, because of its monomeric form and high level of activity, provides an important source of the enzyme for biochemical studies.
