THE MONOAMINE OXIDASES

  Many amines are metabolized by the monoamine oxidase system (MAO). This enzyme system brings about the dehydrogenation of an amine (>CH.NH₂) to an imine (>C=NH), which is then hydrolysed to a carbonyl group. The monoamine oxidases are flavin-dependent systems, which play an important role in the metabolism of the neurotransmitters such as dopamine and many of the drugs, which interact with them. There are two broad families of monoamine oxidase. MAOA for which serotonin is a substrate and MAO-B for which phenylethylamines, e.g. dopamine, are substrates. In this case the corresponding aldehydes are formed. The monoamine oxidases are not always plentiful in the liver and it is possible to ‘flood’ this system, for example, with amine-rich foods.