|Superclasses:||Reactions Classified By Conversion Type → Simple Reactions → Chemical Reactions|
|Reactions Classified By Substrate → Small-Molecule Reactions|
EC Number: 18.104.22.168
Enzymes and Genes:
|Homo sapiens :||xanthine oxidase
Supersedes EC numbers: 22.214.171.124, 126.96.36.199
Note that this reaction equation differs from the official Enzyme Commission reaction equation for this EC number, which can be found here .
The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, 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, and some reactions have been computationally balanced for hydrogen by adding free protons. 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): -161.56125 [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 188.8.131.52, aldehyde oxidase. Under some conditions the product is mainly superoxide rather than peroxide:
The mammallian enzyme predominantly exists as an NAD-dependent dehydrogenase (EC 184.108.40.206, xanthine dehydrogenase). During purification the enzyme is largely converted to the O2-dependent xanthine oxidase form (EC 220.127.116.11). The conversion can be triggered by several mechanisms, including the oxidation of cysteine thiols to form disulfide bonds [Corte72, Ikegami86, Saito89, Okamoto08] [which can be catalysed by EC 18.104.22.168, 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, Okamoto08].
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
Okamoto08: 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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