On rat liver mitochondrial monoamine oxidase activity and lipids

Following earlier observations on the retention of 5-hydroxytryptamine oxidizing activity by a purified preparation of monoamine oxidase from rat liver mitochondria, this fraction has been obtained in a water-soluble form by Triton X-100 gradient gel filtration and DEAE-Bio-Gel A chromatography. The soluble fraction appears to depend on Triton X-100 and phospholipids for its activity. The results seem to implicate membrane lipid components in the expression of rat liver mitochondrial monoamine oxidase activity.     

Molecular weight estimation of bovine brain mitochondrial monoamine oxidase

The molecular size of bovine brain mitochondrial monoamine oxidase (MAO) was investigated Mitochondria were solubilized with an anionic detergent. Emarl 20C, and fractionated by ammonium sulfate. Ammonium sulfate-fractionated MAO was subjected to detergent-containing gel chromatography and detergent-containing gel electrophoresis. MAO activity appeared as single symmetrical peak in gel chromatography in the presence of 1% Emarl 20C, and the molecular weight was estimated to be 44,000. Polymerization of MAO was observed when gel chromatography was performed in lower (0.1%, 0%) concentrations of Emarl 20C. Activity staining of MAO after electrophoresis on a gel containing 0.1% Emar 20C was successful. The molecular weight of MAO estimated from the mobility of this stained band was 89,000. It is suggested that the molecular weight of MAO is 44,000 and that it recombines in low concentrations of the detergent to form complex particles with molecular weights of 89,000 or more.     

Multiple catalytic sites of rat brain mitochondrial monoamine oxidase

We compared the inhibitory and catalytic effects of various monoamines on forms A and B of monoamine oxidase (MAO) on mitochondrial preparations from rat brain in mixed substrate experiments. MAO activity was determined by a radioisotopic assay. MAO showed lower K_m values for tryptamine and β-phenylethylamine than for tyramine and serotonin. The K_m values of the untreated preparation for tyramine, tryptamine, and β-phenylethylamine obtained were the same as those of the form B enzyme and the K_m value for serotonin was the same as that of the form A enzyme. Tyramine and tryptamine were competitive inhibitors of serotonin oxidation and β-phenylethylamine did not bind with form A enzyme or inhibit the oxidation of serotonin, while tyramine and tryptamine were competitive inhibitors of β-phenylethylamine oxidation. Although serotonin was not oxidized by form B enzyme, serotonin was a competitive inhibitor of β-phenylethylamine oxidation. It is suggested that rat brain mitochondrial MAO is characterized by two kinds of binding sites.     

The reaction pathway of membrane-bound rat liver mitochondrial monoamine oxidase

1. A preparation of a partly purified mitochondrial outer-membrane fraction suitable for kinetic investigations of monoamine oxidase is described. 2. An apparatus suitable for varying the O(2) concentration in a spectrophotometer cuvette is described. 3. The reaction catalysed by the membrane-bound enzyme is shown to proceed by a double-displacement (Ping Pong) mechanism, and a formal mechanism is proposed. 4. KCN, NaN(3), benzyl cyanide and 4-cyanophenol are shown to be reversible inhibitors of the enzyme. 5. The non-linear reciprocal plot obtained with impure preparations of benzylamine, which is typical of high substrate inhibition, is shown to be due to aldehyde contamination of the substrate.     

Biochemical characteristics of liver and brain monoamine oxidase from pacu

Monoamine oxidase (MAO) activity in the liver and brain of the pacu, Piaractus mesopotamicus was determined using a fluorescence assay with kynuramine as substrate. Apparent Michaelis constant values (20·33 μM for liver and 25·85 μM for brain) were similar in these tissues, but in terms of tissue protein MAO activity from liver was 4·5 times higher than from brain. The greater inhibitory effects of clorgyline than of deprenyl on MAO activity from liver and brain of this species suggest that pacu's MAO is a type A-like enzyme.     

The effects of disulfiram on rat liver mitochondrial monoamine oxidase.

Monoamine oxidase (MAO) of rat liver mitochondria was found to be inhibited by disulfiram. The inhibition is pH and time dependent: 50% inhibition was observed by 16.5 μM of disulfiram at pH 9.1 after 30 min of preincubation. At pH 7.4 only slight inhibition was produced despite the high concentration of disulfiram (330 μM) and the preincubation period. The inhibition is irreversible and appears to be of mixed type: noncompetitive at low concentration range of the substrate and uncompetitive at high concentration range. Glutathione at twice the concentration of disulfiram abolished the inhibitory effect of the drug. Ethanol, while by itself has only slight effect on MAO activity, enhanced the inhibitory effect of disulfiram at pH 7.4. At pH 9.1, ethanol alone has no effect on MAO; however, it was found to weaken the inhibitory effect of disulfiram.