3unc: Difference between revisions
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== Function == | == Function == | ||
[https://www.uniprot.org/uniprot/XDH_BOVIN XDH_BOVIN] Key enzyme in purine degradation. Catalyzes the oxidation of hypoxanthine to xanthine. Catalyzes the oxidation of xanthine to uric acid. Contributes to the generation of reactive oxygen species. | [https://www.uniprot.org/uniprot/XDH_BOVIN XDH_BOVIN] Key enzyme in purine degradation. Catalyzes the oxidation of hypoxanthine to xanthine. Catalyzes the oxidation of xanthine to uric acid. Contributes to the generation of reactive oxygen species. | ||
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== Publication Abstract from PubMed == | |||
In mammals, xanthine oxidoreductase can exist as xanthine dehydrogenase (XDH) and xanthine oxidase (XO). The two enzymes possess common redox active cofactors, which form an electron transfer (ET) pathway terminated by a flavin cofactor. In spite of identical protein primary structures, the redox potential difference between XDH and XO for the flavin semiquinone/hydroquinone pair (E(sq/hq)) is ~170 mV, a striking difference. The former greatly prefers NAD(+) as ultimate substrate for ET from the iron-sulfur cluster FeS-II via flavin while the latter only accepts dioxygen. In XDH (without NAD(+)), however, the redox potential of the electron donor FeS-II is 180 mV higher than that for the acceptor flavin, yielding an energetically uphill ET. On the basis of new 1.65, 2.3, 1.9, and 2.2 A resolution crystal structures for XDH, XO, the NAD(+)- and NADH-complexed XDH, E(sq/hq) were calculated to better understand how the enzyme activates an ET from FeS-II to flavin. The majority of the E(sq/hq) difference between XDH and XO originates from a conformational change in the loop at positions 423-433 near the flavin binding site, causing the differences in stability of the semiquinone state. There was no large conformational change observed in response to NAD(+) binding at XDH. Instead, the positive charge of the NAD(+) ring, deprotonation of Asp429, and capping of the bulk surface of the flavin by the NAD(+) molecule all contribute to altering E(sq/hq) upon NAD(+) binding to XDH. | |||
Protein conformational gating of enzymatic activity in xanthine oxidoreductase.,Ishikita H, Eger BT, Okamoto K, Nishino T, Pai EF J Am Chem Soc. 2012 Jan 18;134(2):999-1009. Epub 2011 Dec 29. PMID:22145797<ref>PMID:22145797</ref> | |||
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.<br> | |||
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==See Also== | ==See Also== | ||
*[[Xanthine dehydrogenase 3D structures|Xanthine dehydrogenase 3D structures]] | *[[Xanthine dehydrogenase 3D structures|Xanthine dehydrogenase 3D structures]] | ||
== References == | |||
<references/> | |||
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</StructureSection> | </StructureSection> | ||
