Structural, Kinetic, and Pharmacodynarnic Mechanisms of D-Amino Acid Oxidase Inhibition by Small Molecules

We characterized the mechanism and pharmacodynarnics of five structurally distinct inhibitors of D-amino acid oxidase. All inhibitors bound the oxidized form of human enzyme with affinity slightly higher than that of benzoate (K-d approximate to 2-4 mu M). Stopped-flow experiments showed that pyrrole-based inhibitors possessed high affinity (K-d approximate to 100-200 nM) and slow release kinetics (k < 0.01 s(-1)) in the presence of substrate, while inhibitors with pendent aromatic groups altered conformations of the active site lid, as evidenced by X-ray crystallography, and showed slower kinetics of association. Rigid bioisosteres of benzoic acid induced a closed-lid conformation, had slower release in the presence of substrate, and were more potent than benzoate. Steady-state D-serine concentrations were described in a PK/PD model, and competition for D-serine sites on NMDA receptors was demonstrated in vivo. DAAO inhibition increased the spatiotemporal influence of glial-derived D-serine, suggesting localized effects on neuronal circuits where DAAO can exert a neuromodulatory role.