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 fdr to CarAa. Binds 1 [2Fe-2S] cluster per subunit. Monomer. Carbazole 1,9a-dioxygenase complex consists of a terminal oxygenase component CarAa, a ferredoxin reductase component fdr and a ferredoxin component CarAc (Probable). Belongs to the adrenodoxin/putidaredoxin family.