Abstract
Examinations were performed to ascertain the prosthetic groups of rabbit liver mitochondrial monoamine oxidase. This enzyme was inhibited competitively by 8-hydroxyquinoline sulfate. Neocuproine and α, α'-dipyridyl were weak inhibitors, but diethyldithiocarbamate or ethylenediaminetetraacetate were little effective. Cupric ions were available to reactivate the depressed activity of the 8-hydroxyquinoline-treated enzyme. Since recovery was not observed with ferrous ions, the enzyme appeared to be cuproprotein. The second prosthetic group was likely to be sulfhydryl because p-chloromercuribenzoate reacted competitively with the enzyme. Oxidants such as 2-methyl-1, 4-naphthoquinone or β-naphthoquinone-4-sulfonate were also strong inhibitors. Inhibitory effects of 1-benzyl-2-(4, 5, 6, 7-tetrahydro-1, 2-benzisoxazo-3-lyl) carbonylhydrazine hydrochloride (31037-S) and 1-benzyl-2-(3-methylisoxazol-5-yl) carbonylhydrazine (31087-S) were counteracted clearly by the simultaneous addition of some metal ions. Cupric ions were especially efficient. An analogous counteraction was observed with cysteine, while methionine was inert in this phenomenon. The inhibitory action of both hydrazine compounds was likely to be dependent on the blocking of these metal and sulfhydryl groups.
