STUDIES ON MONOAMINE OXIDASE (REPORT XXXIV).

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Abstract
The effects of ammonium sulfate on mitochondrial monoamine oxidase (MAO) in beef liver were studied. The initial stage of the reaction was measured with an oxygen electrode and the long term reaction was measured manometrically. With tyramine or benzylamine as substrate, addition of ammonium sulfate increased the initial reaction but decreased the long term reaction. Ammonium sulfate had similar effects on solubilized MAO. Inhibition of MAO activity in both the initial and long term reaction by excess substrate was diminished by addition of ammonium sulfate. The effects of ammonium sulfate on MAO were reversible. Salts having an -SO4 group, such as Na2SO4 and K2SO4, increased MAO activity in the initial reaction; salts having an -NH4 group, such as NH4Cl and NH4NO3, inhibited it. All salts inhibited MAO activity in the long term reaction. The mechanism of activation of MAO activity by addition of ammonium sulfate is discussed.