Re: What is the action of mono-amine oxidase enzymes (IMAO)

Jesus Mahugo-

Thanks for the great question. I'm not sure if you know the significance of this particular enzyme, but you have hit upon a very important protein.

Monoamine Oxidase is an enzyme that is involved with inactivation of many neurotransmitters. You mentioned serotonin, so let's focus on that particular molecule. The chemical name for serotonin is 5-hydroxytryptamine. It is formed from the amino acid tryptophan, which undergoes a two step transformation. First, the "hydroxyl" group (see picture below) is added. Second, the carboxyl group in tryptophan is removed. In the picture, the location of the carboxyl group present in tryptophan (which is lost in serotonin) is indicated by "site 'C'". See a biochemistry text for the structure of tryptophan, or click here for amino acid information on the web.

The action of monoamine oxidase enzymatically degrades serotonin by cleaving the amine group off, which is referred to as a "deamination" reaction. The two products are ammonium ion (NH4+) and 5-hydroxyindole-3-acetaldehyde. The original tryptophan is not regenerated in this reaction, nor is any amino acid generated from a reaction catalyzed by monoamine oxidase. In all cases, this enzyme merely deactivates neurotransmitters by deaminating them (cleaving an amine group).

That leads to some interesting facts about this enzyme. Because monoamine oxidase is involved with inactivating neurotransmitters, it has been the target of many drug studies. Currently, inhibitors of this enzyme (such as Aurorix) are used in a wide variety of cases, like anti-bipolar depression drugs (1) and treatment of chronic tension-type headache and migraine prophylaxis (2). This approach in treatment is not dissimilar from serotonin anti-reuptake inhibitors like Prozac because inhibition of monoamine oxidase allows the neurotransmitters to remain in the nerve junctions longer, enabling them to work longer. Prozac does the same thing, only it inhibits the uptake machinery in the nerve cell, thus allowing serotonin to be in the junctions longer.

I hope this is clear (and that it answers your question adequately)!

---Brian