Part of the multicomponent carbazole 1,9a-dioxygenase (CARDO), that converts carbazole (CAR) into 2-aminobiphenyl-2,3-diol. Acts as a mediator in the electron transfer from CarAd to CarAa. Binds 1 [2Fe-2S] cluster per subunit. Optimum pH is between 7 and 7.5. Optimum temperature is 30 degrees Celsius. Monomer. Carbazole 1,9a-dioxygenase complex consists of a terminal oxygenase component CarAa, a ferredoxin reductase component CarAd and a ferredoxin component CarAc.