Component of the 2-aminophenol 1,6-dioxygenase (APD) complex that catalyzes the ring fission of 2-aminophenol to produce 2-aminomuconic semialdehyde. CnbCb seems to be the catalytic subunit of the complex. Also active on other substrates such as 2-amino-5-chlorophenol (68% activity), protocatechuate (33% activity) and catechol (5% activity). Both 2-aminophenol and 2-amino-5-cholorophenol are likely native substrates for this dioxygenase which is involved in the reductive degradation pathway of both nitrobenzene (NB) and 4-chloronitrobenzene (4-CNB), allowing C.testosteroni strain CNB-1 to grow on these compounds as sole source of carbon, nitrogen, and energy. 2-aminophenol + O2 = 2-aminomuconate 6-semialdehyde 2-amino-5-chlorophenol + O2 = 2-amino-5-chloromuconate 6-semialdehyde Binds 2 Fe(2+) ions per APD complex. The iron ions are bound to the beta subunit. Complete loss of activity in the presence of Ni(2+), Co(2+), Cd(2+), Zn(2+) and hydrogen peroxide, however activity with hydrogen peroxide partially restored upon addition of excess ascorbate. Partially inhibited by Fe(2+), Mg(2+), Ca(2+), Mn(2+), Cu(2+) and also by EDTA, at 2 mM concentration. Total activity inhibited in the presence of catechol or 4-nitrocatechol but completely restored after removal of catechol and addition of 2 mM Fe(2+) and 5 mM ascorbate. Xenobiotic degradation; nitrobenzene degradation. Xenobiotic degradation; 4-chloronitrobenzene degradation. The APD complex is a heterotetramer of 2 alpha (CnbCa) and 2 beta (CnbCb) subunits. Not active on 4-methylcatechol, 4-chlorocatechol, 2,4-dihydroxybenzoate, o-nitrophenol, p-nitrophenol or 4-nitrocatechol. Belongs to the LigB/MhpB extradiol dioxygenase family. Extended N-terminus.