Aromatic L‐Amino Acid Decarboxylase (AAAD) Activity in Rhesus Macaque Striatum After MAO‐B Inhibition by Ro 16‐6491

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The aromatic L-amino acid decarboxylase (AAAD) (EC enzyme converts L-DOPA to dopamine and is critical in dopamine replacement therapy in Parkinson’s disease (PD). Following stimulated release, the action of synaptic dopamine is terminated by neuronal reuptake and deamination by monoamine oxidase (MAO). While MAO inhibition is known to downregulate tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis (Lamensdorf and Finberg, 1997), the effect of MAO inhibition on AAAD is unclear. There are two MAO subtypes based on substrate and inhibitor specificity, MAO-A and MAO-B (Kinemuchi et al., 1984). Dopamine is effectively deaminated by both subtypes, but MAO-B has higher activity than MAO-A in the primate striatum, suggesting that MAO-B plays a greater role than MAO-A in striatal dopamine metabolism in primates (Paterson et al., 1995). By slowing dopamine degradation and maximizing L-DOPA efficacy, MAO-B inhibitors may be useful in PD therapy, as suggested by Napolitano et al. (1995).

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