Cholinesterase

Neurotransmission is mediated by the neurotransmitter acetylcholine (ACh). Acetylcholine is released at synapse as a means for one neuron to communicate with a neighboring neuron. Upon release, ACh is rapidly hydrolyzed into choline and acetic acid terminating the signal. This is accomplished by a family of enzymes called cholinesterase (ChE). There are two types of cholinesterase. The two forms differ genetically, structurally, and functionally.

  • Acetylcholinesterase (AChE), also called true cholinesterase and tissue esterase, is an enzyme that catalyzes the hydrolysis of acetylcholine to choline and acetate. It is present in nerve tissue, red blood cells of the spleen, and gray matter of the brain. It inactivates acetylcholine at nerve junctions and regulates muscle contractions. AChE is one of the most efficient of enzymes, terminating transmission within milliseconds after acetylcholine release.
  • Butyrylcholinesterase (BuChE), formerly called pseudocholinesterase, also called plasma cholinesterase, is found in blood and liver. Its function in normal situations is unknown. Individuals who are genetically incapable of making this enzyme are normal in all other respects. Butyrylcholinesterase is responsible for metabolism of succinylcholine and certain drugs which are not metabolized by AChE. Succinylcholine is a neuromuscular blocking agent used in anesthesia to produce skeletal muscle paralysis. It acts by inhibiting true cholinesterase. BuChE has received an increased interest in Alzheimer's disease patients, as recent data from cortex of these patients has shown that as the disease progresses, concentrations of AChE decline dramatically, while activity of BuChE shows some increase 2. In addition to genetic deficiencies, low levels of BuChE activity can be seen following exposure to organophosphate insecticides, during pregnancy, and in patients with liver disease.

References

  1. Lippincott Williams & Wilkins. Deciphering Diagnostic Tests
  2. Italo Biaggioni, David Robertson, Geoffrey Burnstock, Phillip A. Low, Julian F.R. Paton (editors). Primer on the Autonomic Nervous System
  3. Anthony A. Killeen. Principles of Molecular Pathology
  4. George A. Mashour, Ralph Lydic. Neuroscientific Foundations of Anesthesiology