 The catechol dioxygenases, some of the most well-studied dioxygenase enzymes, use dioxygen to cleave a carbon-carbon bond of an aromatic catechol ring system.Catechol dioxygenases are further classified as being “extradiol” or “intradiol,” and this distinction is based on mechanistic differences in the reactions (figures 1 & 2).Intradiol enzymes cleave the carbon-carbon bond between the two hydroxyl groups.