Monoamine oxidase B, also known as MAOB, is an enzyme that in humans is encoded by the MAOB gene. The protein encoded by this gene belongs to the flavin monoamine oxidase family. It is an enzyme located in the outer mitochondrial membrane. It catalyzes the oxidative deamination of biogenic and xenobiotic amines and plays an important role in the catabolism of neuroactive and vasoactive amines in the central nervous system and peripheral tissues (such as dopamine). This protein preferentially degrades benzylamine and phenethylamine. Similarly to monoamine oxidase A (MAOA), it also degrades dopamine [though some new research contradicts this, suggesting that MAOB does not directly degrade dopamine, but is responsible for GABA synthesis]. Structure Monoamine oxidase B has a hydrophobic bipartite elongated cavity that (for the "open" conformation) occupies a combined volume close to 700 Å3. hMAO-A has a single cavity that exhibits a rounder shape and is larger in volume than the "substrate cavity" of hMAO-B. The first cavity of hMAO-B has been termed the entrance cavity (290 Å3), the second substrate cavity or active site cavity (~390 Å3) – between both an isoleucine199 side-chain serves as a gate. Depending on the substrate or bound inhibitor, it can exist in either an open or a closed form, which has been shown to be important in defining the inhibitor specificity of hMAO B. At the end of the substrate cavity is the FAD coenzyme with sites for favorable amine binding about the flavin involving two nearly parallel tyrosyl (398 and 435) residues that form what has been termed an aromatic cage. Differences between MAOA and MAOB MAO-A is involved in the metabolism of tyramine; inhibition, in particular irreversible inhibition of MAO-A can result in a dangerous pressor effect when foods high in tyramine are consumed such as cheeses (informally known as the "cheese effect"). MAO-A is involved in the metabolism of serotonin, noradrenaline and dopamine whereas MAO-B metabolises the dopamine neurotransmitter. MAO-B is an enzyme on the outer mitochondrial membrane and catalyzes the oxidation of arylalkylamine neurotransmitters Monoamine oxidase A (MAOA) generally metabolizes tyramine, norepinephrine (NE), serotonin (5-HT), and dopamine (DA) (and other less clinically relevant chemicals). In contrast, monoamine oxidase B (MAOB) mainly metabolizes dopamine (DA) (and other less clinically relevant chemicals). The differences between the substrate selectivity of the two enzymes are utilized clinically when treating specific disorders: Monoamine oxidase A inhibitors have been typically used in the