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

Effects of 3'-Me-DAB on MAO in rat liver mitochondria, in vitro, were investigated. 3'-Me-DAB at a concentration of 1 x 10(-5) M inhibits MAO activity about 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. These results indicate that 3'-Me-DAB binds to mitochondrial MAO with a weak affinity in vitro. The Km value toward benzylamine was 220 microM 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.