ABSTRACT
Human thyroid monoamine oxidase from hyperfunctioning thyroids was isolated and purified by separating the mitochondria by differential centrifugation followed by ultrasonication. The suspension containing the active enzyme from the DEAE-column, on passing through a Sephadex G-200 column gave three peaks corresponding to molecular weights of approximately 220,000, 23,000 and 4000 of which the component with molecular weight 4000 showed enzyme activity. The blood of the patients was analyzed for plasma MAO, RBC cholinesterase, plasma histaminase and plasma catecholamines. Histology and histochemistry of the thyroid tissues were also done. The data are examined from the point of view of the prevalent idea of the possible existence of MAO in multiple forms.