Component of the 2-aminophenol 1,6-dioxygenase complex that catalyzes the ring fission of 2-aminophenol to produce 2-aminomuconic 6-semialdehyde. AmnB seems to be the catalytic subunit of the complex. The enzyme is also active toward 2-amino-p-cresol, 6-amino-m-cresol, 2-amino-m-cresol, 2-amino-4,5-dimethylphenol, 2-amino-4-chlorophenol, and catechol. 2-aminophenol + O2 = 2-aminomuconate 6-semialdehyde Binds 1 Fe(2+) ion per subunit. Strongly inhibited by CuSO(4), FeCl(3), K(3)[Fe(CN)(6)], AgNO3, HgCl(2) and MnCl(2). Heterotetramer of 2 alpha and 2 beta subunits. Belongs to the LigB/MhpB extradiol dioxygenase family.