Dioxygenases cleave the aromatic rings of their substrates by inserting two oxygen atoms, thus degrading these compounds. The dioxygenases are divided into 2 groups according to their mode of ring scission. The intradiol enzymes use Fe+3 as cofactor and cleave the substrate between 2 hydroxyl groups. The extradiol enzymes use Fe+2 as cofactor and cleave the substrate between a hydroxylated carbon and a non-hydroxylated one.
- Protocatechuate 3,4-dioxygenase (PCD), belongs to the intradiol family and catalyzes the oxygenation of dihydroxybenzoate (DHB) to 3-carboxy-muconate. PCD participates in the aromatic compound benzoate degredation and uses Fe as cofactor. PCD consists of 8 subunits each containing an Fe and a substrate binding site. Each of these subunits is composed of α and β chains. Hydroxyphenyl acetate is an inhibitor of PCD.
- Catechol 1,2-dioxygenase (CTD) cleaves the ring of catechol by insertion of 2 oxygen atoms to form muconic acid.
- Homoprotocatechuate 3,4-dioxygenase (HPCD), an extradiol cleaving enzyme cleaves the aromatic ring of its substrate, adds 2 oxygen atoms to form α-hydroxy-δ carboxymethyl muconic semialdehyde.
- Naphthalene 1,2-dioxygenase (NDO) catalyzes the conversion of naphthalene and O2 to dihydronaphthalene-diol.
