Characteristics of Rat Skull Benzylamine Oxidase

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Abstract
Benzylamine oxidase (BzAO) is an amine oxidase with a widespread distribution in mammalian tissues. Certain properties of BzAO were characterized using homogenate of rat skull as the enzyme source. BzAO activity was assayed after inactivation of monoamine oxidases with pargyline and was distinct from diamine oxidase, polyamine oxidase, lysyl oxidase and ceruloplasmin. Only aromatic amines with a primary amino group interacted with BzAO. 2-Phenylethylamine, tryptamine, p-tyramine and dopamine acted as substrates but were deaminated less rapidly than benzylamine, which showed an apparent Km value of 2.8 .mu.M and a Vmax value of 220 pmol deaminated mg.cntdot.protein-1.cntdot.min-1. (+)-.alpha.-Methylphenylethylamine (amphetamine) acted as a noncompetitive inhibitor of benzylamine deamination. Overall, the Km and Ki values of the amines for BzAO increased with increasing polarity. The nonprotonated form of benzylamine probably acts as substrate for the enzyme and the catalytic mechanism of skull BzAO appears consistent with a double displacement or ping-pong reaction. Compared with brain monoamine oxidase [EC 1.4.3.4] type B, benzylamine is 50 times more avid for BzAO, which, in turn, appears to exhibit a lower Km for oxygen than monoamine oxidase type B.