Xanthine oxidase
| xanthine oxidase/dehydrogenase | |||||||||
|---|---|---|---|---|---|---|---|---|---|
Crystallographic structure (monomer) of bovine xanthine oxidase.
The bounded FAD (red), FeS-cluster (orange), the molybdopterin cofactor with molybdenum (yellow) and salicylate (blue) are indicated. |
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| Identifiers | |||||||||
| EC number | 1.17.3.2 | ||||||||
| CAS number | 9002-17-9 | ||||||||
| Databases | |||||||||
| IntEnz | IntEnz view | ||||||||
| BRENDA | BRENDA entry | ||||||||
| ExPASy | NiceZyme view | ||||||||
| KEGG | KEGG entry | ||||||||
| MetaCyc | metabolic pathway | ||||||||
| PRIAM | profile | ||||||||
| PDB structures | RCSB PDB PDBe PDBsum | ||||||||
| Gene Ontology | AmiGO / EGO | ||||||||
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| Search | |
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| PMC | articles |
| PubMed | articles |
| NCBI | proteins |
| xanthine oxidase/dehydrogenase | |
|---|---|
| Identifiers | |
| Symbol | XDH |
| Entrez | 7498 |
| HUGO | 12805 |
| OMIM | 607633 |
| PDB | 1FIQ |
| RefSeq | NM_000379 |
| UniProt | P47989 |
| Other data | |
| EC number | 1.17.3.2 |
| Locus | Chr. 2 p23.1 |
Xanthine oxidase (XO, sometimes 'XAO') is a form of xanthine oxidoreductase, a type of enzyme that generates reactive oxygen species. These enzymes catalyze the oxidation of hypoxanthine to xanthine and can further catalyze the oxidation of xanthine to uric acid. These enzymes play an important role in the catabolism of purines in some species, including humans.
Xanthine oxidase is defined as an enzyme activity (EC 1.17.3.2). The same protein, which in humans has the HGNC approved gene symbol XDH, can also have xanthine dehydrogenase activity (EC 1.17.1.4). Most of the protein in the liver exists in a form with xanthine dehydrogenase activity, but it can be converted to xanthine oxidase by reversible sulfhydryl oxidation or by irreversible proteolytic modification.
The following chemical reactions are catalyzed by xanthine oxidase:
hypoxanthine (one oxygen atom)
xanthine (two oxygens)
uric acid (three oxygens)
Because XO is a superoxide-producing enzyme, with general low specificity, it can be combined with other compounds and enzymes and create reactive oxidants, as well as oxidize other substrates.
Bovine xanthine oxidase (from milk) was originally thought to have a binding site to reduce with, but it has been found that the mechanism to reduce this protein is through XO's superoxide anion byproduct, with competitive inhibition by carbonic anhydrase.
Another reaction catalyzed by xanthine oxidase is the decomposition of S-Nitrosothiols (RSNO), a reactive nitrogen species, to nitric oxide (NO), which reacts with a superoxide anion to form peroxynitrite under aerobic conditions.
XO has also been found to produce the strong one-electron oxidant carbonate radical anion from oxidation with acetaldehyde in the presence of catalase and bicarbonate. It was suggested that the carbonate radical was likely produced in one of the enzyme's redox centers with a peroxymonocarbonate intermediate.
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