Abstract
Effects of oxygen concetration on MAO activity in beef brain mitochondria with various amines as substrates were investigated. The MAO activity was assayed by measuring oxygen consumption by the Warburg manometric method at 38°C. It was found that the changes in oxygen concentration caused significant effects in MAO activity and the affinity of enzyme to oxygen with tyramine as substrate was differ from that of enzyme with serotonin. In addition, the following results were obtained.
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1) The substrate specificities of beef brain mitochondrial MAO in 20% and 100% oxygen concentration were investigated. In 20% oxygen concentration, the MAO activity with dopamine as substrate was found to be greatest and was followed with tyramine, tryptamine, serotonin and β-phenylethylamine. On the other hand, in 100% oxygen concentration, the greatest MAO activity was found with tyramine as substrate, and was followed with dopamine, tryptamine, β-phenylethylamine and serotonin. All activities, mentioned above, proceeded lineally within the initial 20 minutes.
The changes in MAO activity with changes in oxygen concentration between 5 to 100% were investigated. The MAO activites with tyramine as substrate was decreased by the decrease in oxygen concentration from 100 to 5%. However, the MAO activites with benzylamine and serotonin as substrate were changed markedly only when the oxygen concentration was below 20%, while no chang was observed when it was above 20%.
3) The Km values against oxygen with tyramine, tryptamine and dopamine as substrate were 133 pM and that with serotonin as substrate were 50 pM.
4) The inhibition of MAO by catronwith tyramine as substrate was noncompetitive against oxygen and with serotonin as substrate was competitive.
