MetaCyc Reaction:

Superclasses: Reactions Classified By Conversion TypeSimple ReactionsChemical Reactions
Reactions Classified By SubstrateSmall-Molecule Reactions

EC Number:

Enzymes and Genes:

Homo sapiens: xanthine oxidase: XDH

Supersedes EC numbers:,

Note that this reaction equation differs from the official Enzyme Commission reaction equation for this EC number, which can be found here .

The direction shown, i.e. which substrates are on the left and right sides, is in accordance with the direction in which it was curated.

Most BioCyc compounds have been protonated to a reference pH value of 7.3. Please see the PGDB Concepts Guide for more information.

Mass balance status: Balanced.

Enzyme Commission Primary Name: xanthine oxidase

Enzyme Commission Synonyms: hypoxanthine oxidase, hypoxanthine:oxygen oxidoreductase, Schardinger enzyme, xanthine oxidoreductase, hypoxanthine-xanthine oxidase, xanthine:O2 oxidoreductase, xanthine:xanthine oxidase

Taxonomic Range: Metazoa

Standard Gibbs Free Energy (ΔrG in kcal/mol): -161.56125Inferred by computational analysis [Latendresse13]

This is an alternative reaction catalyzed by xanthine oxidase under some conditions.

Enzyme Commission Summary:
An iron-molybdenum flavoprotein (FAD) containing [2Fe-2S] centres. Also oxidizes hypoxanthine, some other purines and pterins, and aldehydes, but different from EC, aldehyde oxidase. Under some conditions the product is mainly superoxide rather than peroxide:

an organic molecule + H2O + 2 oxygen → an alcohol + 2 superoxide + 2 H+

The mammallian enzyme predominantly exists as an NAD-dependent dehydrogenase ( EC, xanthine dehydrogenase). During purification the enzyme is largely converted to the O2-dependent xanthine oxidase form (EC The conversion can be triggered by several mechanisms, including the oxidation of cysteine thiols to form disulfide bonds [Corte72, Ikegami86, Saito89, Okamoto08a] [which can be catalysed by EC, enzyme-thiol transhydrogenase (glutathione-disulfide) in the presence of glutathione disulfide] and limited proteolysis, which results in irreversible conversion. The conversion can also occur in vivo [Engerson87, Okamoto08a].

Citations: [Battelli82, Carpani90, Eger00]

Gene-Reaction Schematic

Gene-Reaction Schematic

Relationship Links: BRENDA:EC:, ENZYME:EC:, IUBMB-ExplorEnz:EC:

Created 16-Sep-2011 by Caspi R, SRI International


Battelli82: Battelli MG, Lorenzoni E (1982). "Purification and properties of a new glutathione-dependent thiol:disulphide oxidoreductase from rat liver." Biochem J 207(1);133-8. PMID: 6960894

Carpani90: Carpani G, Racchi M, Ghezzi P, Terao M, Garattini E (1990). "Purification and characterization of mouse liver xanthine oxidase." Arch Biochem Biophys 279(2);237-41. PMID: 2350174

Corte72: Corte ED, Stirpe F (1972). "The regulation of rat liver xanthine oxidase. Involvement of thiol groups in the conversion of the enzyme activity from dehydrogenase (type D) into oxidase (type O) and purification of the enzyme." Biochem J 126(3);739-45. PMID: 4342395

Eger00: Eger BT, Okamoto K, Enroth C, Sato M, Pai EF, Nishino T (2000). "Purification, crystallization and preliminary X-ray diffraction studies of xanthine dehydrogenase and xanthine oxidase isolated from bovine milk." Acta Crystallogr D Biol Crystallogr 56(Pt 12);1656-8. PMID: 11092937

Engerson87: Engerson TD, McKelvey TG, Rhyne DB, Boggio EB, Snyder SJ, Jones HP (1987). "Conversion of xanthine dehydrogenase to oxidase in ischemic rat tissues." J Clin Invest 79(6);1564-70. PMID: 3294898

Ikegami86: Ikegami T, Nishino T (1986). "The presence of desulfo xanthine dehydrogenase in purified and crude enzyme preparations from rat liver." Arch Biochem Biophys 247(2);254-60. PMID: 3459393

Latendresse13: Latendresse M. (2013). "Computing Gibbs Free Energy of Compounds and Reactions in MetaCyc."

Okamoto08a: Okamoto K, Eger BT, Pai EF, Nishino T (2008). "Mammalian xanthine oxidoreductase - mechanism of transition from xanthine dehydrogenase to xanthine oxidase." FEBS J 275(13);3278-89. PMID: 18513323

Saito89: Saito T, Nishino T, Tsushima K (1989). "Interconversion between NAD-dependent and O2-dependent types of rat liver xanthine dehydrogenase and difference in kinetic and redox properties between them." Adv Exp Med Biol 253B;179-83. PMID: 2610112

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Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
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