Monoamine oxidase A (for "Amine oxidase [flavin-containing] A") and Monoamine oxidase B (for "Amine oxidase [flavin-containing] B") (MAO-A (Monoamine oxidase A), MAO-B (Monoamine oxidase B))

Monoamine oxidases are flavin-dependent enzymes located on the outer mitochondrial membrane that catalyze the oxidative deamination of primary and some secondary amines—including key neurotransmitters—producing corresponding aldehydes/ketones along with ammonia and hydrogen peroxide. There are two isoforms in humans: • **Monoamine oxidase A (MAOA)** preferentially metabolizes serotonin (5-hydroxytryptamine), norepinephrine, epinephrine. • **Monoamine oxidase B (MAOB)** preferentially metabolizes phenylethylamine and benzylamine but also acts on dopamine. These enzymes play a critical role in regulating neurotransmitter levels within both central nervous system neurons and peripheral tissues. Their dysfunction is implicated in various neuropsychiatric conditions; thus they are established therapeutic targets for antidepressants (**MAOI class**) as well as anti-Parkinsonian drugs (**selective MAO-B inhibitors**).

Other names

Amine oxidase [flavin-containing] AAmine oxidase [flavin-containing] BMAOAMAOBMonoamine oxidase type A/B

Drugs targeting these enzymes are typically **irreversible or reversible inhibitors** that block the oxidative deamination activity, thereby increasing synaptic concentrations of monoamines such as serotonin, dopamine, or norepinephrine. This underlies their use in depression and Parkinson’s disease therapy.