The degradation of aromatic compounds by aerobic bacteria frequently begins with the dihydroxylation of the substrate by nonhaem iron-containing dioxygenases. These enzymes consist of two or three soluble proteins that interact to form an electron-transport chain that transfers electrons from reduced nucleotides (NADH) via flavin and [2Fe-2S] redox centres to a terminal dioxygenase [<cite idref="PUB00000122"/>].Aromatic-ring-hydroxylating dioxygenases oxidise aromatic hydrocarbons and related compounds to cis-arene diols. These enzymes utilise a mononuclear non-haem iron centre to catalyse the addition of dioxygen to their respective substrates. <p>Naphthalene 1,2-dioxygenase (NDO) from <taxon tax_id="110517">Pseudomonas sp. NCIB9816-4</taxon> has a domain structure and iron coordination of the Rieske domain is very similar to that of the cytochrome bc1 domain. The active-site iron centre of one of the alpha subunits is directly connected by hydrogen bonds through a single amino acid, Asp205, to the Rieske [2Fe-2S] centre in a neighbouring alpha subunit. This may be the main route for electron transfer [<cite idref="PUB00005305"/>].</p>