The termcholinesterase is sometimes used to refer specifically to butyrylcholinesterase,[2] but thisusage produces the oddity thatcholinesterase andfalse cholinesterase (pseudocholinesterase) under that scheme mean the same thing[2] (confusingly), and acetylcholinesterase is then calledtrue cholinesterase in contrast,[2] producing the second oddity thatcholinesterase andtrue cholinesterase then do not mean the same thing. But such usage is now outdated; the current, unambiguousHGNC names and symbols are acetylcholinesterase (AChE) and butyrylcholinesterase (BChE).
Acetylcholinesterase (EC3.1.1.7) (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 theblood onred blood cell membranes, inneuromuscular junctions, and in other neuralsynapses. 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.[3]
Butyrylcholinesterase (EC3.1.1.8) (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 theliver and found primarily inblood plasma. Thebutyl andbutyryl syllables both refer tobutane with one of its terminalmethyl groups substituted.
The half-life of BChE is approximately 10 to 14 days.[4] BChE levels may be reduced in patients with advancedliver disease. The decrease must be greater than 75% before significant prolongation of neuromuscular blockade occurs withsuccinylcholine.[5][6]
An absence or mutation of the BCHE enzyme leads to a medical condition known aspseudocholinesterase deficiency. This is a silent condition that manifests itself only when people that have the deficiency receive the muscle relaxantssuccinylcholine ormivacurium during a surgery.
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.
The presence of ACHE in the amniotic fluid may be tested in early pregnancy. A sample of amniotic fluid is removed byamniocentesis, and presence of ACHE can confirm several common types of birth defect, includingabdominal wall defects andneural tube defects.[12]
Some early research points to genetic butylcholinesterase deficiency as a possible candidate component insudden infant death syndrome.[13]
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 developstrigger points.[14][15]
Acholinesterase inhibitor (or "anticholinesterase") suppresses the action of the enzyme. Because of its essential function, chemicals that interfere with the action of cholinesterase are potentneurotoxins, causing excessive salivation and eye-watering in low doses, followed by muscle spasms and ultimately death (examples are somesnake venoms, and the nerve gasessarin andVX). One counteracting medication ispralidoxime. The so-called nerve gases and many substances used in insecticides have been shown to act by combining with a residue of serine in the active site of acetylcholine esterase, inhibiting the enzyme completely. The enzyme acetylcholine esterase breaks down the neurotransmitter acetylcholine, which is released at nerve and muscle junctions, in order to allow the muscle or organ to relax. The result of acetylcholine esterase inhibition is that acetylcholine builds up and continues to act so that any nerve impulses are continually transmitted and muscle contractions do not stop.
Among the most common acetylcholinesterase inhibitors are phosphorus-based compounds, which are designed to bind to the active site of theenzyme. The structural requirements are aphosphorus atom bearing twolipophilic groups, a leaving group (such as ahalide orthiocyanate), and aterminaloxygen. The entry onLawesson's reagent has some details on one sub-class of the phosphorus-based compounds.
^Shinde R, Chatterjea MN (2005).Textbook of Medical Biochemistry (6th ed.). New Delhi: Jaypee Brothers Medical Publications (P) Ltd. p. 565.ISBN978-93-5025-484-4.
^Holmes JH, Kanfer I, Zwarenstein H (Aug 1978). "Effect of benzodiazepine derivatives on human blood cholinesterase in vitro".Research Communications in Chemical Pathology and Pharmacology.21 (2):367–70.PMID29327.
