Cholinesterase

acetylcholinesterase (Yt blood group)
Identifiers
Symbol	ACHE
Alt. symbols	YT
NCBI gene	43
HGNC	108
OMIM	100740
RefSeq	NM_015831
UniProt	P22303
Other data
EC number	3.1.1.7
Locus	Chr. 7 q22
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butyrylcholinesterase
Identifiers
Symbol	BCHE
Alt. symbols	CHE1
NCBI gene	590
HGNC	983
OMIM	177400
RefSeq	NM_000055
UniProt	P06276
Other data
EC number	3.1.1.8
Locus	Chr. 3 q26.1-26.2
Search for Structures Swiss-model Domains InterPro

In biochemistry, cholinesterase is a term which refers to one of the two enzymes:

• Acetylcholinesterase (EC 3.1.1.7) (AChE), also known as RBC cholinesterase, erythrocyte cholinesterase, or (most formally) acetylcholine acetylhydrolase, found primarily in the blood and neural synapses
• Pseudocholinesterase (EC 3.1.1.8) (BChE or BuChE), also known as plasma cholinesterase, butyrylcholinesterase, or (most formally) acylcholine acylhydrolase, found primarily in the liver

Both of these compounds catalyze the hydrolysis of the neurotransmitter acetylcholine into choline and acetic acid, a reaction necessary to allow a cholinergic neuron to return to its resting state after activation.

The difference between the two types of cholinesterase has to do with their respective preferences for substrates: the former hydrolyses acetylcholine more quickly; the latter hydrolyses butyrylcholine more quickly. In 1968, Walo Leuzinger et al successfully purified and crystallized the enzyme from electric eels at Columbia University, NY. The 3D structure of acetylcholinesterase was first determined in 1991 by Sussman et al using protein from the Pacific electric ray.

An absence or mutation of the pseudocholinesterase enzyme leads to a medical condition known simply as pseudocholinesterase deficiency. This is a silent condition that only manifests itself when people who have the deficiency receive the muscle relaxants succinylcholine or mivacurium during a surgery.

Cholinesterase inhibitors

A cholinesterase inhibitor (or "anticholinesterase") suppresses the action of the enzyme. Because of its essential function, chemicals that interfere with the action of cholinesterase are potent neurotoxins, causing excessive salivation and eye watering in low doses, followed by muscle spasms and ultimately death (examples are some snake venoms, and the nerve gases sarin and VX). One counteracting medication is pralidoxime.

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 terminal oxygen. The entry on Lawesson's reagent has some details on one sub-class of the phosphorus-based compounds.

Outside of biochemical warfare, anticholinesterases are also used in anesthesia or in the treatment of myasthenia gravis, glaucoma and Alzheimer's disease. Also, 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.

Reference

• Leuzinger W, Baker AL..ACETYLCHOLINESTERASE, I. LARGE-SCALE PURIFICATION, HOMOGENEITY, AND AMINO ACID ANALYSIS. Proc Natl Acad Sci U S A. 1967 Feb; 57(2): 446-451. PMCID: 335526
• Leuzinger W, Baker A L, Cauvin E. Acetylcholinesterase, II. Crystallization, Absorption Spectra, Isoionic Point. Proc Natl Acad Sci U S A, Vol. 59, No. 2 (Feb. 15, 1968), pp. 620-623. PMCID: 224717
• Sussman JL, Harel M, Frolow F, Oefner C, Goldman A, Toker L, Silman I. Atomic structure of acetylcholinesterase from Torpedo californica: a prototypic acetylcholine-binding protein. Science 1991;253:872-9. PMID 1678899.

External links

• Movies showing the structure of acetylcholinesterase and interactions with various inhibitors.
• Acetylcholinesterase: Molecule of the Month on PDB