Intradiol dioxygenases catalyze the critical ring-cleavage step in the conversion of catecholate derivatives to citric acid cycle intermediates. This family contains catechol 1,2-dioxygenases and protocatechuate 3,4-dioxygenases which are mononuclear non-heme iron enzymes that catalyze the oxygenation of catecholates to aliphatic acids via the cleavage of aromatic rings. The members are intradiol-cleaving enzymes which break the catechol C1-C2 bond and utilize Fe3+, as opposed to the extradiol-cleaving enzymes which break the C2-C3 or C1-C6 bond and utilize Fe2+ and Mn+. Catechol 1,2-dioxygenases are mostly homodimers with one catalytic ferric ion per monomer. Protocatechuate 3,4-dioxygenases form more diverse oligomers.
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