Aromatic-ring-hydroxylating dioxygenases (ARHD) incorporate two atoms of dioxygen (O2) into their substrates in the dihydroxylation reaction.
Two prosthetic groups, a Rieske-type [Fe2S2] center and a mononuclear iron, are associated with the α-subunit in the (αβ)n-type enzymes.
In benzoate and toluate 1,2-dioxygenase systems, a single protein containing reductase and Rieske-type ferredoxin domains transfers the electrons from NADH to the hydroxylase component.
The overall fold is very similar to that of the soluble fragment of the Rieske protein from bovine heart mitochondrial cytochrome bc1 complex.
The iron of the active site is located at the bottom of a narrow channel, approximately 15 Å from the protein surface.