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The enzyme cholinesterase (EC 3.1.1.8, choline esterase; systematic name acylcholine acylhydrolase) catalyses the hydrolysis of choline-based :
Several of these serve as . Thus, it is either of two that catalyst the hydrolysis of these cholinergic neurotransmitters, such as breaking acetylcholine into choline and acetic acid. These reactions are necessary to allow a cholinergic neuron to return to its resting state after activation. For example, in muscle contraction, acetylcholine at a neuromuscular junction triggers a contraction; but for the muscle to relax afterward, rather than remaining locked in a tense state, the acetylcholine must be broken down by a choline esterase. The main type for that purpose is acetylcholinesterase (also called choline esterase I or erythrocyte cholinesterase); it is found mainly in and red blood cell membranes. The other type is butyrylcholinesterase (also called choline esterase II or plasma cholinesterase); it is found mainly in the blood plasma.
The term cholinesterase is sometimes used to refer specifically to butyrylcholinesterase, but this usage produces the oddity that cholinesterase and false cholinesterase ( pseudocholinesterase) under that scheme mean the same thing (confusingly), and acetylcholinesterase is then called true cholinesterase in contrast, producing the second oddity that cholinesterase and true cholinesterase then do not mean the same thing. But such usage is now outdated; the current, unambiguous HGNC names and symbols are acetylcholinesterase (AChE) and butyrylcholinesterase (BChE).
Acetylcholinesterase () (AChE), also known as choline esterase I, RBC cholinesterase, or erythrocyte cholinesterase, true cholinesterase, choline esterase I, or (most formally) acetylcholine acetylhydrolase, is found primarily in the blood on red blood cell membranes, in neuromuscular junctions, and in other neural . Acetylcholinesterase exists in multiple molecular forms. In the mammalian brain the majority of AChE occurs as a tetrameric, G4 form (10) with much smaller amounts of a monomeric G1 (4S) form.
Butyrylcholinesterase () (BChE), also known as cholinesterase, choline esterase II, BuChE, pseudocholinesterase (PCE), plasma cholinesterase (PChE), serum cholinesterase (SChE), butylcholinesterase, or (most formally) acylcholine acylhydrolase, is produced in the liver and found primarily in blood plasma. The butyl and butyric acid syllables both refer to butane with one of its terminal substituted.
The half-life of BChE is approximately 10 to 14 days. BChE levels may be reduced in patients with advanced liver disease. The decrease must be greater than 75% before significant prolongation of neuromuscular blockade occurs with succinylcholine. (2025). 9780781757454, Lippincott Williams & Wilkins. ISBN 9780781757454
The 3D structure of acetylcholinesterase was first determined in 1991 by Joel Sussman et al. using protein from the Pacific electric ray.
Clinically useful quantities of butyrylcholinesterase were synthesized in 2007 by PharmAthene, through the use of genetically modified goats.
Pseudocholinesterase deficiency may also affect local anaesthetic selection in dental procedures. The enzyme plays an important role in the metabolism of ester-based local anaesthetics, a deficiency lowers the margin of safety and increases the risk of systemic effects with this type of anaesthetic. The selection of an amide-based solution is recommended in such patients.
Elevation of plasma BCHE levels was observed in 90.5% of cases of acute myocardial infarction. (2025). 9789350254844, Jaypee Brothers Medical Publications (P) Ltd.. ISBN 9789350254844
The presence of ACHE in the amniotic fluid may be tested in early pregnancy. A sample of amniotic fluid is removed by amniocentesis, and presence of ACHE can confirm several common types of birth defect, including abdominal wall defects and neural tube defects. FBR Resource Guide: Acetylcholinesterase-Amniotic Fluid . Foundation for Blood Research (September 7, 2007). Retrieved on 2007-11-21.
BCHE can be used as a prophylactic agent against nerve gas and other organophosphate poisoning.
Some early research points to genetic butylcholinesterase deficiency as a possible candidate component in sudden infant death syndrome.
The enzyme Acetylcholin esterase, and its inhibition, plays a role in the development of myofascial trigger points and the associated myofascial pain syndrome. By injecting a mouse with acetylcholin esterase inhibitors and electrical stimulation, the muscle develops trigger points.
Among the most common acetylcholinesterase inhibitors are phosphorus-based compounds, which are designed to bind to the active site of the enzyme. The structural requirements are a phosphorus atom bearing two lipophilic groups, a leaving group (such as a halide or thiocyanate), and a Polymer oxygen. The entry on Lawesson's reagent has some details on one sub-class of the phosphorus-based compounds.
Some benzodiazepines, e.g., temazepam have an inhibitory effect on cholinesterase.
Cholinesterase levels can be used as an indirect marker of arsenic exposure.
Outside of biochemical warfare, anticholinesterases are also used for reversing medication induced paralysis during anesthesia; as well as in the treatment of myasthenia gravis, glaucoma, and Alzheimer's disease. Such compounds are used for killing insects in a range of products including sheep dip, organophosphate pesticides, and carbamate pesticides. In addition to acute poisoning as described above, a semi-acute poisoning characterized by strong mental disturbances can occur. Also, prolonged exposure can cause birth defects.
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