ENZYME

ENZYME entry: EC 1.17.3.2

Accepted Name

Xanthine oxidase.

Alternative Name(s)

Hypoxanthine oxidase.

Hypoxanthine-xanthine oxidase.

Schardinger enzyme.

Xanthine oxidoreductase.

Reaction catalysed

Xanthine + H(2)O + O(2) <=> urate + H(2)O(2)

Cofactor(s)

FAD; Iron-sulfur; Molybdopterin.

Comment(s)

Also oxidizes hypoxanthine, some other purines and pterins, and aldehydes, but is distinct from EC 1.2.3.1.
Under some conditions the product is mainly superoxide rather than peroxide: R-H + H(2)O + 2 O(2) = ROH + 2 O(2)(.-) + 2 H(+).
The mammallian enzyme predominantly exists as an NAD-dependent dehydrogenase (EC 1.17.1.4).
During purification the enzyme is largely converted to the O(2)- dependent xanthine oxidase form (EC 1.17.3.2).
The conversion can be triggered by several mechanisms, including the oxidation of cysteine thiols to form disulfide bonds (which can be catalyzed by EC 1.8.4.7 in the presence of glutathione disulfide) or limited proteolysis, which results in irreversible conversion.
The conversion can also occur in vivo.
Formerly EC 1.1.3.22 and EC 1.2.3.2.

Cross-references

PROSITE

BRENDA

EC2PDB

ExplorEnz

PRIAM enzyme-specific profiles

KEGG Ligand Database for Enzyme Nomenclature