Component of the 2-aminophenol 1,6-dioxygenase complex that catalyzes the ring fission of 2-aminophenol to produce 2-aminomuconic 6-semialdehyde. AmnA seems to have a role in the stability of the complex. Heterotetramer of 2 alpha and 2 beta subunits. Belongs to the LigB/MhpB extradiol dioxygenase family. In contrast to other members of the family, lacks the conserved iron-binding sites, suggesting it has no oxidoreductase activity.