Time-dependent inhibition of monoamine oxidase by β-phenethylamine

Abstract

Several reports have suggested that monoamine oxidase activity towards β-phenethylamine is inhibited by high concentrations of that substrate. This inhibition is not found if initial velocities are measured, but there is a slower time-dependent inhibition at higher β-phenethylamine concentrations. Such time-dependent inhibition is not found with tyramine as substrate or upon incubation of the enzyme with the reversible inhibitor amphetamine. The inhibition is not due to the accumulation of phenacetaldehyde, phenylethanol or phenacetic acid, or to a reaction of any of these three products either with each other or with β-phenethylamine. Although the inhibition is time-dependent, the inactivated enzyme slowly regains activity upon removal of the β-phenethylamine. A model is proposed to explain the observed inhibition.