<p>This group represents a 3-hydroxyanthranilate 3,4-dioxygenase found in metazoan species, especially animals. 3-Hydroxyanthranilic acid 3,4-dioxygenase (3HAO) is a non-heme ferrous extradiol dioxygenase in the kynurenine pathway from tryptophan. It catalyzes the conversion of 3-hydroxyanthranilate (HAA) to quinolinic acid (QUIN), an endogenous neurotoxin, via the activation of N-methyl-D-aspartate (NMDA) receptors and the precursor of NAD+ biosynthesis [<cite idref="PUB00043312"/>]. Kynurenine pathway metabolism has been implicated in neurological disease [<cite idref="PUB00043313"/>].</p>