The role of CDO may vary between cell types as it can either be used primarily for taurine or sulfate production or for degradation of cysteine.

[2][3][8] Furthermore, crystal structures show the amino nitrogen and thiolate sulfur of cysteine coordinated to the iron in addition to a single water molecule (see figure).

[2] CDO contains a unique internal cofactor created by intramolecular thioether formation between Cys93 and Tyr157, which is postulated to participate in catalysis.

Crosslinking increases efficiency of CDO ten-fold and is regulated by levels of cysteine, an unusual example of protein cofactor formation mediated by substrate (feedforward activation).

[3] Studies have shown that the cysteinyltyrosine bridge lowers the oxidation potential of tyrosine (commonly an electron donor, as in photosystem II) by ~0.5 V relative to phenol and increases its acidity.

Other studies have shown that Tyr157 is needed for enzyme function (possibly as a tyrosinyl radical) and is highly conserved across CDO variants.

[10][11][12] Heterolytic O-O bond cleavage then affords a high-valent iron (IV) oxo intermediate (C), which transfers the second oxygen to sulfur.

[1] CDO deficiency and subsequent cysteine accumulation in the globus pallidus has been linked to Pantothenate kinase-associated neurodegeneration.

[16] These results suggest that CDO1 (human cysteine dioxygenase type I) acts as a tumor suppressor gene and may potentially serve as a biomarker for cancer.