3-hydroxyanthranilate 3,4-dioxygenase () is an enzyme encoded by the HAAO gene that catalyzes the chemical reaction
The two substrates of this enzyme are 3-hydroxyanthranilic acid and oxygen. Its product is 2-amino-3-carboxymuconic semialdehyde.
This enzyme belongs to the family of oxidoreductases, specifically those acting on single donors with O<sub>2</sub> as oxidant and incorporation of two atoms of oxygen into the substrate (oxygenases). The oxygen incorporated need not be derived from O<sub>2</sub>.
The systematic name of this enzyme class is 3-hydroxyanthranilate:oxygen 3,4-oxidoreductase (decyclizing). Other names in common use include 3-hydroxyanthranilate oxygenase, 3-hydroxyanthranilic acid oxygenase, 3-hydroxyanthranilic oxygenase, 3-hydroxyanthranilic acid oxidase and 3HAO. This enzyme participates in tryptophan metabolism. It employs one cofactor, iron.
As of late 2007, 6 structures have been solved for this class of enzymes, with PDB accession codes , , , , , and .h