The effect of tris buffers on rat liver mitochondrial monoamine oxidase

The effect of tris buffers upon the monoamine oxidase (MAO) activity in rat liver mitochondria has been investigated. Tris buffer was shown to inhibit MAO in a non-competitive manner with a Ki of 15-25 mM. Tyramine, 5-hydroxytryptamine and beta-phenethylamine but not benzylamine oxidations were all inhibited by tris buffer. All inhibitions, except that of 5-HT, were completely reversible. It is suggested that these effects are produced by conformational changes in the structure of the MAO. The significance of these results is discussed with respect to the use of tris buffers in the extraction and estimation of the activity of MAO.