Effect of tris (hydroxymethyl) aminomethane on amine oxidase activity in dog brain, liver and serum and in human placenta.

The effect of Tris (hydroxymethyl) aminomethane on mitochondrial monoamine oxidase (MAO) activity in dog brain and liver and in human placenta was studied and the results obtained were compared with results on dog serum amine oxidase. With benzylamine as substrate, Tris did not inhibit mitochondrial MAO activity in these preparations, whereas inhibited mitochondrial MAO activity in these preparations, whereas it inhibited amine oxidase activity in a serum preparation. However, with tyramine, 5-hydroxytryptamine or beta-phenylethylamine as substrate, Tris inhibited MAO activity in all these preparations and its mode of inhibition was found to be non-competitive and reversible. The inhibition of Tris of MAO activity in these preparations was not due to decrease in the extent of extraction of aldehydes produced during the enzyme reaction. Moreover, increase in the oxygen tension did not change the extent of inhibition of MAO activity by Tris. From these results, it is concluded that with benzylamine as substrate, there is a remarkable difference in the effects of Tris on amine oxidase activity in mitochondrial and serum preparations. This difference in the inhibitions of mitochondria and serum is discussed.