STUDIES ON MONOAMINE OXIDASE (REPORT XXV) EFFECTS OF ALCOHOLS ON BEEF LIVER MITOCHONDRIAL MONOAMINE OXIDASE

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The effects of alcohols on MAO activity in beef and rat liver mitochondria were studied. MAO activity was determined manometrically using tyramine (1×10-2 M) as substrate and expressed as O2 uptake in 60 min. At concentrations of 0.1 to 10%, methanol and ethanol increased MAO activity in both beef and rat liver mitochondria. Activation of MAO by ethanol was reversible. Ethanol increased MAO activity of beef liver mitochondria using butylamine, amylamine, benzylamine, beta-phenylethylamine, tryptamine or serotonin as substrate. The pH optima of MAO in beef liver mitochondria were at pH 7.0 and pH 7.5 in the absence and presence of ethanol. On addition of 1% ethanol, the Km value (2×10-2 M) did not change but the Vmax vlaue increased two-fold. The pS-activity curve of MAO was sigmoidal and on addition of ethanol, MAO was inhibited by a high concentration of substrate. Ethanol decreased the inhibition of MAO by pheniprazine or pargyline. These results suggest that addition of ethanol does not affect the dissociation constant of the enzyme-substrate complex, but accelerates reaction steps occurring after the enzyme-substrate complex has been formed.
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