Monoamine Oxidase (MAO)

metabolism by MAO

  • Concentrated in the liver and kidney, but otherwise present all over the body
  • Present mainly in the outer mitochondrial surface
  • Present in sympathetic nerve terminals, and metabolizes released neurotransmitter
  • Deaminates catecholamines, BUT…
    • They have to have an amine group without too large a substituent, AND
    • They cannot have a substituent at the alpha carbon (like, say amphetamine does)

MAO-A

    • Peripherally, located in the syncytiotrophoblast of the term placenta, and in the liver
    • Centrally, found in noradrenegeric neurons, mainly locus coeruleus

MAO-B

    • Peripherally, located in the platelets, lymphocytes and the liver
    • Centrally, found in serotonergic neurons

Catechol -O- methyltransferase (COMT)

    • Concentrated in the liver and kidney, but otherwise present all over the body
    • Present mainly in the cytoplasm

metabolism by COMT

  • THIS IS THE ENZYME that metabolizes most of intravenously administered catecholamines
  • Exchanges the hydroxyl group at the 3 position on the catechol ring for a methyl group, BUT…
    • The catecholamine ring MUST be intact with 2 hydroxyl groups, otherwise it wont work

References

For this sort of really basic stuff, no matter where you look you will find essentially the same information.


I used chapters from "Goodman & Gilman's The Pharmacological Basis of Therapeutics" 11th ed by Brunton et al, and "Basic & Clinical Pharmacology" 11th ed. By Katzung et al.

I also perused Peck and Hill "Pharmacology for Anaesthesia and Intensive care" as well as the notoriously error-prone "Handbook of Pharmacology and Physiology in Anaesthetic Practice" by Stoelting and Hillier. Neither covered this subject in a depth I found satisfying.

Goodman and Gilman's remains a canonical text.