Monoamine oxidases (singular abbreviation MAO) (EC 1.4.3.4) are enzymes that catalyze the oxidation of monoamines.
They are found bound to the outer membrane of mitochondria in most cell types in the body. They belong to protein family of flavin containing amine oxidoreductases.
Monoamine oxidases catalyze the oxidative deamination of monoamines. Oxygen is used to remove an amine group from a molecule, resulting in the corresponding aldehyde and ammonia.
MAO-A and MAO-B
In humans there are two types of MAO: MAO-A and MAO-B.
Both are found in neurons and astroglia.
Outside the central nervous system:
MAO-A is also found in the liver, gastrointestinal tract and placenta.
MAO-B is mostly found in blood platelets.
References
Shih JC, Chen K, Ridd MJ. Monoamine oxidase: from genes to behavior. Annu Rev Neurosci. 1999;22:197-217. PMID: 10202537