Monoamine Oxidase - Substrate Specificities

Substrate Specificities

They are well known enzymes in pharmacology, since they are the substrate for the action of a number of monoamine oxidase inhibitor drugs. MAO-A is particularly important in the catabolism of monoamines ingested in food. Both MAOs are also vital to the inactivation of monoaminergic neurotransmitters, for which they display different specificities.

  • Serotonin, melatonin, noradrenaline, and adrenaline are mainly broken down by MAO-A.
  • Phenethylamine and benzylamine are mainly broken down by MAO-B.
  • Both forms break down dopamine, tyramine, and tryptamine equally.

Specific reactions catalyzed by MAO include:

  • Adrenaline or noradrenaline to 3,4-Dihydroxymandelic acid
  • Metanephrine or normetanephrine to vanillylmandelic acid (VMA)
  • Dopamine to dihydroxyphenylacetic acid
  • 3-Methoxytyramine to homovanillic acid

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