Purification and Properties of Mitochondrial Monoamine Oxidase Type A from Skipjack Liver

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Monoamine oxidase A (EC 1. 4. 3. 4) in skipjack liver was extracted from mitochondrial prepara-tions by Triton X-100. The enzyme was purified by ammonium sulfate fractionation, followed by chro-matographies of Sephadex G-200, Butyl Toyopearl 650M, and hydroxyapatite. By this method a final specific activity of 19.5 units/mg and 30-fold purification were attained.
The molecular weight of the final preparation was estimated to be about 130, 000 by gel filtration on Sephadex G-200. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated asubunit molecular mass of 64, 000. The optimum pH was 9.0 and the enzyme was stable between pH 9.0 and 10.0 after incubation at 4°C for 60 min. The optimum temperature was 30°C. The enzyme was in-hibited by Ca²⁺, Mg²⁺ and Mn²⁺, but was activated by Cu²⁺. Theenzyme showed a high activity by 5-hydroxytryptamine, tyramine and epinephrine assubstrates, but showed low activity by benzylamine and 2-phenylethylamine.