A benzylamine oxidase distinct from monoamine oxidase B—Widespread distribution in man and rat

Benzylamine oxidase (BzAO) and monoamine oxidase type B(MAO-B) both selectively catalyse the oxidative deamination of benzylamine (Bz). We define the former as that benzylamine-metabolizing activity insensitive to 4 × 10^?4 M deprenyl, a concentration which totally inhibits all forms of MAO. Although both enzymes are widespread in human and rat tissues, their organ distribution differs. Liver and brain show highest MAO-B activity, whilst BzAO activity predominates in aorta and lung. Relatively low BzAO and no MAO-B activity is present in plasma. In the rat, phenylethylamine (PEA) and dopamine (DA) are both substrates for a deprenyl-resistant enzyme with a distribution similar to BzAO, but in man these amines are solely oxidized by MAO. At pH 7.2 the K_m of BzAO for benzylamine is 2.2 × ^?4 M in the rat; μn man, it is 1.1 × 10^?4M. The K_m of MAO-B for benzylamine is 1.0 × 10^?4M in the rat and 5 × 10^?5 in man. Semicarbazide, procarbazine and carbidopa are potent inhibitors of BzAO and inhibit it selectively, leaving MAO substantially unaffected.