Inhibition of copper-dependent amine oxidases by some hydrazides of pyrrol-1-ylbenzoic and pyrrol-1-ylphenylacetic acids.

Some hydrazides of pyrrol-1-ylbenzoic and pyrrol-1-ylphenylacetic acids were prepared, and their effect on copper-dependent amine oxidases (Cu-AOs) and FAD monoamine oxidases (MAOs) activities was tested. The compounds were not substrates for Cu-AO enzymes but acted as noncompetitive inhibitors. Hydrazides of pyrrol-1-ylphenylacetic acids were highly specific for plasma amine oxidase (Ki = 0.5-1 microM). In contrast, all the hydrazides were weak inhibitors of MAO activity. Incubation with the hydrazide derivatives led to irreversible inactivation of Cu-AOs. Therefore, the inhibition implied two distinct steps. The first one consisted of the rapid formation of the enzyme-inhibitor complex and was reversed by dialysis. In the second step, the complex was irreversibly transformed, probably by the formation of a Schiff base between the hydrazide and the prosthetic carbonyl group of the enzyme.