Inhibition of monoamine oxidase by 3'-methyl-4-dimethylamino azobenzene (3'-Me-DAB) in rat liver mitochondria.

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Abstract
Effects of 3''-Me-DAB [3''-methyl-4-dimethylaminoazobenzene], a carcinogenic dye, on MAO [monoamine oxidase]in rat liver mitochondria in vitro were investigated. 3''-Me-DAB 1 .times. 10-5 M inhibits MAO activity .apprx. 40%, and this inhibition recovered to the control value after dialysis overnight against 0.001 M phosphate buffer. MAO activity was inhibited in an apparently competitive fashion by 3''-Me-DAB. Evidently, 3''-Me-DAB bonds to mitochondrial MAO with a weak affinity in vivo. The Km value toward benzylamine was 220 .mu.M using both the mitochondria from the liver of rats fed a basal diet and those from rats ingesting 3''-Me-DAB. The activity of these enzyme preparations did not revert after dialysis to the control values of rats fed a basal diet. The titration experiment of MAO by pargyline suggests that the decrease of MAO activity in vitro is mainly due to the decrease of active MAO molecules in these mitochondrial preparations from livers of rats ingesting 3''-Me-DAB.