Dioxygenases

Dioxygenases are enzymes that catalyze the incorporation of both atoms of molecular oxygen into a substrate. They are a subset of oxidoreductases and are distinguished from monooxygenases, which transfer one oxygen atom to a substrate while reducing the other to water. In dioxygenase reactions, the substrate is oxidized by the simultaneous addition of two oxygen atoms, which may be incorporated as hydroxyl groups or used to cleave chemical bonds.

Dioxygenases employ diverse metal cofactors and catalytic architectures. Many non-heme iron(II) dioxygenases use an iron center to activate O2, while Rieske-type oxygenases contain a Rieske [2Fe-2S] cluster in conjunction with a mononuclear iron site in a multi-component system. Heme-containing dioxygenases also exist, exemplified by certain tryptophan catabolic enzymes.

Biological roles include the degradation of aromatic compounds by soil and marine bacteria, enabling the breakdown of pollutants such as catechol, benzoate, and polycyclic aromatics. They also participate in biosynthetic pathways that form natural products and signaling molecules.

Notable examples include catechol 1,2-dioxygenase and catechol 2,3-dioxygenase, which cleave the catechol ring by intradiol and extradiol mechanisms, respectively; benzoate dioxygenase; and naphthalene dioxygenase. Indoleamine 2,3-dioxygenase is a heme-containing dioxygenase that oxidizes tryptophan in immune and metabolic pathways.

Dioxygenases are of interest in environmental biotechnology for bioremediation and in pharmaceutical and industrial contexts for biocatalysis and synthesis, reflecting their central role in oxygen transfer during metabolic transformations.