Purification and characterization of monoamine oxidase from Klebsiella aerogenes

The gene for monoamine oxidase (maoA) from Klebsiella aerogenes W70 has been cloned and the enzyme was overproduced in a soluble form. The enzyme was purified approximately 10-fold to homogeneity. The enzyme has a molecular weight of about 79,000, which is identical to the molecular weight deduced from the nucleotide sequence of the gene for monoamine oxidase. The enzyme had maximum activity at pH 6.0 and 50°C when catalyzing the oxidative deamination of tyramine. The enzyme catalyzed the deamination of β-phenylethylamine, dopamine, tryptamine, and octopamine, but not of diamines, polyamines, or amino acids. The enzyme was inhibited by clorgyline, isoniazid, and carbonyl reagents, but not by 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide. The enzyme did not exhibit a typical flavoprotein spectrum, but the enzymatic activity increased linearly with increasing amounts of added copper. The purified enzyme was found to contain 10 g of copper per 79,000 g of the protein. The enzymological properties and the amino acid sequence of the enzyme deduced from the nucleotide sequence of the moaA gene are different from those of known tyramine or monoamine oxidases.