extradiol

Extradiol is a biochemical term used to describe a type of ring-cleavage reaction of aromatic compounds in which the carbon–carbon bond broken is located adjacent to one of the hydroxyl groups on an aromatic dihydroxy substrate. This mode is contrasted with intradiol (ortho) cleavage, in which the ring is opened between the two hydroxyls. The reactions are carried out by extradiol dioxygenases, a family of non-heme iron enzymes that incorporate both atoms of molecular oxygen into the substrate and cleave the ring at the meta position.

In catechol metabolism, catechol 2,3-dioxygenase catalyzes extradiol cleavage of catechol to 2-hydroxymuconic semialdehyde. This product then enters downstream pathways that convert it into intermediates usable for central metabolism.

These enzymes are widespread in bacteria and fungi and participate in the catabolism of various aromatic compounds, including phenols, catechols, toluene and xylene derivatives, and chlorinated aromatics. The meta-cleavage pathways allow organisms to utilize these compounds as carbon and energy sources. Extradiol dioxygenases contribute to the breakdown of environmental pollutants and the turnover of natural aromatics in soils and water.

Due to their role in environmental pollutant degradation, extradiol dioxygenases are of interest for bioremediation and biotechnological applications. Research continues to understand substrate specificity, structure, and regulation to enhance their utility in cleanup strategies and industrial biocatalysis.