RESUMO
The kinetics of inhibition of the activity of monoamine oxidases A (with 5-oxytryptamine as substrate) and B (with 2-phenylethylamine as substrate) from rat liver mitochondria by a new acetyleneamine, 1-(indolyl-3)isopropylmethylpropargylamine, was studied. It was shown that the inhibition of the both forms of monoamine oxidase results in formation of an intermediate dissociating enzyme--inhibitor complex which is further converted into an irreversibly blocked enzyme. The value of the dissociation constant, Ki, of the intermediate enzyme--inhibitor complex with 2-phenylethylamine as substrate is equal to 24 . 10(6) M, that with 5-oxytryptamine--to 0.09 . 10(-6) M. The values of the rate constants, K3, for the conversion of the enzyme--inhibitor complex into an irreversibly blocked enzyme in experiments with 2-phenylethylamine and 5-oxytryptamine were rather close, i. e. 0.06 and 0.05 min-1, respectively. The results obtained indicate that the selectivity and inhibition of the activity of monoamine oxidases A and B by propargylamine derivatives is manifested at the primary step of formation of dissociating intermediate enzyme--inhibitor complexes.
