Abstract
The substrate specificities and affinities of oxygen for monoamine oxidase (MAO) in beef, rabbit and rat livers and in human placenta were studied. MAO activity was determined by measuring oxygen consumption using Warburg's manometer at 38°C and expressed as μ1 O2. Tyramine was most strongly oxidized by beef liver, rat liver and human placenta mitochondrial MAO in comparison to other substrates. PEA was more strongly oxidized than other substrates by rabbit liver. Each mitochondrial enzyme preparation was treated with one per cent Emulgen 810. After the solubilization of each enzyme preparation with this detergent, MAO activities decreased by about 30 % with each substrate, but substrate specificity was not changed, except for in the case of human placenta. That is, tryptamine oxidation often increased with solubilization of MAO in human placenta. High affinity for oxygen was observed with benzylamine or serotonin oxidation and low affinity for oxygen was observed with PEA oxidation. Affinities for oxygen were not changed by solubilization of MAO in rat liver, while the affinity with human placenta increased after solubilization. These results suggest that the classification of MAO in terms of substrate specificity was not relate to its classification in terms of affinity for oxygen.
