Editing Xanthine oxidase (section)

=== Other reactions ===
Because XO is a superoxide-producing enzyme, with general low specificity,<ref name="MG Bonini et al">{{cite journal | vauthors = Bonini MG, Miyamoto S, Di Mascio P, Augusto O | title = Production of the carbonate radical anion during xanthine oxidase turnover in the presence of bicarbonate | journal = The Journal of Biological Chemistry | volume = 279 | issue = 50 | pages = 51836–43 | date = December 2004 | pmid = 15448145 | doi = 10.1074/jbc.M406929200 | s2cid = 20161424 | doi-access = free }}</ref> 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 [[cytochrome c]] 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]].<ref name="JM McCord & I. Fridovich">{{cite journal |last1=McCord |first1=J M |last2=Fridovich |first2=I |title=The Reduction of Cytochrome c by Milk Xanthine Oxidase |journal=Journal of Biological Chemistry |date=November 1968 |volume=243 |issue=21 |pages=5753–5760 |doi=10.1016/S0021-9258(18)91929-0 |pmid=4972775 |doi-access=free }}</ref>

Another reaction catalyzed by xanthine oxidase is the decomposition of ''S''-nitrosothiols (RSNO), a class of reactive nitrogen species, to nitric oxide (NO), which reacts with a superoxide anion to form peroxynitrite under aerobic conditions.<ref name="M Trujillo">{{cite journal | vauthors = Trujillo M, Alvarez MN, Peluffo G, Freeman BA, Radi R | title = Xanthine oxidase-mediated decomposition of S-nitrosothiols | journal = The Journal of Biological Chemistry | volume = 273 | issue = 14 | pages = 7828–34 | date = April 1998 | pmid = 9525875 | doi = 10.1074/jbc.273.14.7828 | s2cid = 10221482 | doi-access = free }}</ref>

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.<ref name="MG Bonini et al" />

Here is a diagram highlighting the pathways catalyzed by xanthine oxidase.

[[File:Xanthine oxidase pathways.jpg|frameless|A diagram illustrating many of the pathways catalyzed by xanthine oxidase.]]

It is suggested that xanthine oxidoreductase, along with other enzymes, participates in the conversion of nitrate to nitrite in mammalian tissues.<ref>{{Cite journal |pmid = 18516050|year = 2008|last1 = Jansson|first1 = E. A.|last2 = Huang|first2 = L.|last3 = Malkey|first3 = R.|last4 = Govoni|first4 = M.|last5 = Nihlén|first5 = C.|last6 = Olsson|first6 = A.|last7 = Stensdotter|first7 = M.|last8 = Petersson|first8 = J.|last9 = Holm|first9 = L.|last10 = Weitzberg|first10 = E.|last11 = Lundberg|first11 = J. O.|title = A mammalian functional nitrate reductase that regulates nitrite and nitric oxide homeostasis|journal = Nature Chemical Biology|volume = 4|issue = 7|pages = 411–7|doi = 10.1038/nchembio.92}}</ref>