Partial Separation and Properties of Mitochondrial Monoamine Oxidase in Brain*

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Abstract
Monoamine oxidase was partially separated from beef brain mitochondria by the combined effects of the use of a detergent Cutscum (1.2%, pH 7.1) and of sonication (20 kc, 4 min., twice). The activity was followed by the disappearance of kynuramine. About 70% of the original activity was liberated into solution after the treatments. The activity stayed in the supernatant after the centrifugation at 105,000 x g for 3 hr. The solubilized preparation was unstable. Rapid separation by DEAE [diethylaminoethyl] cellulose column chromatography resulted in only 6-fold purification from the original homogenate. The properties of solubilized brain monoamine oxidase were examined. The enzyme was a sulfhydryl enzyme in so far as it was inhibited by p-chloromercuribenzoate. Some metal chelating agents inhibited the activity. The inhibition by sodium diethyldithiocarbamate and cuprizone may be indicative of Cu involvement as a cofactor. The following biogenic amines besides kynuramine could be deaminated by the solubilized enzyme preparation; tryptamine, serotonin, tyramlne, dopamine, nore-pinephrlne, and epinephrine. The pH-activity curve showed an optimum between pH 7.5 and 8.0 when kynuramine was used as substrate. Several inhibitors of monoamine oxidase of therapeutic and pharmacological interest, markedly inhibited the activity at concentrations as low as 1 x 10-5 M.