Mode of action and characteristics of monoamine oxidase-A inhibition by moclobemide.

The mode of interaction of the reversible monoamine oxidase-A (MAO-A) inhibitor moclobemide with the enzyme was investigated. The inhibition of rat brain or human placenta MAO-A by moclobemide showed an initial competitive phase, with a relatively low affinity (KI = 0.2-0.4 mM). However, the potency of the inhibitor was increased with incubation time. The time-dependent component of the association of moclobemide with MAO-A followed pseudo-first order kinetics. In contrast to mechanism-based inhibitors, no indication for adduct or product formation was detected after incubation of moclobemide with the enzyme. Even though some aspects of the moclobemide interaction with MAO-A are still not completely elucidated, this compound seems to have the characteristics of a slow-binding inhibitor.