monoaminooxidasa

Monoaminooxidasa, more commonly called monoamine oxidase (MAO), refers to a family of flavin-dependent enzymes located on the outer mitochondrial membrane that catalyze the oxidative deamination of monoamines such as serotonin, norepinephrine, dopamine, and trace amines. Two isoforms, MAO-A and MAO-B, are produced by distinct genes and differ in substrate preference and tissue distribution.

MAO-A preferentially deaminates serotonin and norepinephrine and is abundant in the gut and placenta, as well as in certain brain regions. MAO-B preferentially metabolizes phenethylamine and is prominent in platelets and many areas of the brain. Both isoforms metabolize dopamine to varying extents, and together they regulate the levels of monoamines in the central nervous system and periphery.

Biochemically, MAO enzymes use flavin adenine dinucleotide (FAD) as a cofactor and perform oxidative deamination to yield an aldehyde, ammonia, and hydrogen peroxide as byproducts.

Clinical relevance includes the use of monoamine oxidase inhibitors (MAOIs) in the treatment of depression and, in some cases, Parkinson’s disease. Irreversible inhibitors such as phenelzine, isocarboxazid, and tranylcypromine nonselectively inhibit MAO-A and MAO-B, whereas selective or reversible inhibitors (for example moclobemide for MAO-A and selegiline or rasagiline for MAO-B) are also used.

Inhibition of MAO raises concerns about drug and food interactions. Nonselective MAOIs can cause hypertensive crises when foods rich in tyramine are ingested; combination with certain antidepressants or serotonergic drugs can risk serotonin syndrome. Dietary and drug restrictions are important in MAOI therapy.