Monoamine oxidase substrates and substrate affinity.

The evidence that there are two forms of monoamine oxidase (MAO) enzymes is reviewed. On the basis of various substrate affinities, differential inhibition by deprenyl and clorgyline, and heat inactivation, there appear to be a type A and a type B MAO in various tissues. The enzymatic oxidation of telemethylhistamine (tMH) is an example of an endogenous substrate for type B MAO.