Aniline dioxygenase is a multicomponent Rieske nonheme-iron dioxygenase enzyme isolated from Acinetobactersp. strain YAA. Saturation mutagen-esis of the substrate-binding pocket residues, which were identified using a homology model of theasubunit of the terminal dioxygenase (AtdA3), was used to probe the molecular determinants of AtdA substrate specificity.