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Abstract
Quinolinic acid (QUIN), a well-known excitotoxin, was found to inhibit type B monoamine
oxidase (MAO-B) in human brain synaptosomal mitochondria. By kinetic analysis, the
inhibition of MAO-B activity by QUIN was competitive with the substrate, kynuramine.
On the other hand, type A MAO (MAO-A) activity in human brain synaptosomal mitochondria
and human placental mitochondria was not affected by QUIN. The selective inhibition
of MAO-B by QUIN was confirmed using human liver mitochondria; only MAO-B was inhibited
by QUIN and MAO-A was not inhibited. The inhibition was completely reversible. Among
compounds structurally related to QUIN, 4-pyrimidine carboxaldehyde was the most potent
substrate-competitive inhibitor of MAO-B, while 3-hydroxyanthranilic acid and xanthrenic
acid, other metabolites of tryptophan, inhibited MAO non-competitively with the substrate.
The inhibition of MAO-B by QUIN may be related to the causes of the neurotoxicity
of QUIN.