Species: [Clostridium] purinilyticum
Subunit composition of xanthine dehydrogenase = [xanthine dehydrogenase α subunit]4[xanthine dehydrogenase β subunit]4[xanthine dehydrogenase γ subunit]4
xanthine dehydrogenase is a seleno-molybdo-iron-sulfur flavoprotein that belongs to the family of molybdenum hydroxylases. These enzymes contain FAD, a molybdenum cofactor, and at least one Fe/S center. In addition, these proteins have an additional sulfur or selenium atom, which is required for activity. The enzyme lacks selenocysteine, and contains selenium in a relatively unstable form, and only rarely contains the full complement of 2 mol Se per mol of enzyme [Meyer00, Self00].
The enzyme from [Clostridium] purinilyticum has been purified 349-fold to homogeneity [Self00]. It is a large complex composed of three different subunits, possibly containing 4 copies of each. Unlike similar enzymes from related organisms, the enzyme from [Clostridium] purinilyticum was not sensitive to oxygen, and was stable in the presence of air.
Hydroxylation of the purine ring occurs at the 8-position. The enzyme accepts several purine compouds as substrates, but the Km value of other substrates is much higher than that for xanthine (4.5 μM), suggesting that the later is probably the preferred substrate in vivo [Self00].
Molecular Weight: 529 kD (experimental) [Self00]
Enzymatic reaction of: xanthine dehydrogenase
EC Number: 18.104.22.168xanthine + NAD+ + H2O ← urate + NADH + H+
The direction shown, i.e. which substrates are on the left and right sides, is in accordance with the Enzyme Commission system.
This reaction is reversible.Alternative Substrates for xanthine: allopurinol [Self00], 2-hydroxypurine [Self00], hypoxanthine [Self00], 1-methylxanthine [Self00]
In Pathways: purine nucleobases degradation I (anaerobic)hydrogen cyanide [Self00]Kinetic Parameters:
Molecular Weight: 80 kD (experimental) [Self00]
Molecular Weight: 35 kD (experimental) [Self00]
Molecular Weight: 16 kD (experimental) [Self00]
Meyer00: Meyer O, Gremer L, Ferner R, Ferner M, Dobbek H, Gnida M, Meyer-Klaucke W, Huber R (2000). "The role of Se, Mo and Fe in the structure and function of carbon monoxide dehydrogenase." Biol Chem 381(9-10);865-76. PMID: 11076018
Park06: Park YJ, Yoo CB, Choi SY, Lee HB (2006). "Purifications and characterizations of a ferredoxin and its related 2-oxoacid:ferredoxin oxidoreductase from the hyperthermophilic archaeon, Sulfolobus solfataricus P1." J Biochem Mol Biol 39(1);46-54. PMID: 16466637
Self00: Self WT, Stadtman TC (2000). "Selenium-dependent metabolism of purines: A selenium-dependent purine hydroxylase and xanthine dehydrogenase were purified from Clostridium purinolyticum and characterized." Proc Natl Acad Sci U S A 97(13);7208-13. PMID: 10860985
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