Electron transfer
A large family of multicomponent mononuclear (non-heme) iron oxygenases has been identified. Components of bacterial aromatic-ring dioxygenases constitute two different functional classes: hydroxylase components and electron transfer components. Hydroxylase components are either (αβ)"n" or (α)"n" oligomers. Two prosthetic groups, a Rieske-type [Fe2S2] center and a mononuclear iron, are associated with the α-subunit in the (αβ)"n"-type enzymes. Electron transfer components are composed of flavoprotein (NADH:ferredoxin oxidoreductase) and Rieske-type [Fe2S2] ferredoxin. 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. In the phthalate 4,5-dioxygenase system, phthalate dioxygenase reductase (PDR) has the same function. PDR is a single protein comprising FMN-binding reductase and plant-type ferredoxin domains. Thus, the electron transfer in ARHD systems can be summarised as: