Xanthine oxidase

Xanthine oxidase

The enzyme xanthine oxidase, or XO, (bovine milk enzyme is PDB|1FIQ, EC number|1.17.3.2) catalyzes the oxidation of hypoxanthine to xanthine and can further catalyze the oxidation of xanthine to uric acid. This enzyme plays an important role in the catabolism of purines in some species, including humans.

Reaction

* hypoxanthine + O2 + H2O ↔ xanthine + H2O2
* xanthine + O2 + H2O ↔ uric acid + H2O2

Protein structure

The protein is large, having a molecular weight of 270,000, and has 2 flavin molecules (bound as FAD), 2 molybdenum atoms, and 8 iron atoms bound per enzymatic unit. The molybdenum atoms are contained as molybdopterin cofactors and are the active sites of the enzyme. The iron atoms are part of [2Fe-2S] ferredoxin iron-sulfur clusters and participate in electron transfer reactions.

Active site and mechanism of xanthine oxidase

The active site of XO is composed of a molybdopterin unit with the molybdenum atom also coordinated by terminal oxygen (oxo), sulfur atoms and a terminal hydroxide. In the reaction with xanthine to form uric acid, an oxygen atom is transferred from molybdenum to xanthine. The reformation of the active molybdenum center occurs by the addition of water. Like other known molybdenum-containing oxidoreductases, the oxygen atom introduced to the substrate by XO originates from water rather than from dioxygen (O2).

Xanthine oxidase and disease

In humans, xanthine oxidase is normally found in the liver and not free in the blood. During severe liver damage, xanthine oxidase is released into the blood, so a blood assay for XO is a way to determine if liver damage has happened. As well, because xanthine oxidase is a metabolic pathway for uric acid formation, the xanthine oxidase inhibitor allopurinol is used in the treatment of gout.

Xanthinuria is a rare genetic disorder where the lack of xanthine oxidase leads to high concentration of xanthine in blood and can cause health problems such as renal failure. There is no specific treatment, sufferers are advised by doctors to avoid foods high in purine and to maintain a high fluid intake.

ee also

* Allopurinol
* sodium molybdate

References

*

*

*cite journal
author = Hille R.
title = Structure and Function of Xanthine Oxidoreductase
journal= European Journal of Inorganic Chemistry
year = 2006
volume = 2006
issue = 10
pages= 1905–2095
doi = 10.1002/ejic.200600087

External links

*


Wikimedia Foundation. 2010.

Игры ⚽ Поможем сделать НИР

Look at other dictionaries:

  • xanthine oxidase — n a crystallizable flavoprotein enzyme containing iron and molybdenum that promotes the oxidation esp. of hypoxanthine and xanthine to uric acid and of many aldehydes to acids called also Schardinger enzyme * * * xan·thine ox·i·dase… …   Medical dictionary

  • xanthine oxidase — xanthine oxidase. См. фермент Шардингера. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • xanthine oxidase — noun : a crystallizable flavoprotein enzyme containing iron and molybdenum that promotes the oxidation especially of hypoxanthine and xanthine to uric acid and of many aldehydes to acids and that is obtained usually from milk or liver * * *… …   Useful english dictionary

  • xanthine oxidase — Dehydrogenases involved in conversion of hypoxanthine to xanthine, and xanthine to uric acid, as the final catabolism of purines. Deficient in the human disease xanthinuria …   Dictionary of molecular biology

  • xanthine oxidase — noun A crystallizable flavoprotein enzyme containing iron and molybdenum that promotes the oxidation especially of hypoxanthine and xanthine to uric acid and of many aldehydes to carboxylic acids and that is obtained usually from milk or liver …   Wiktionary

  • Xanthine — Not to be confused with xanthene. Xanthine …   Wikipedia

  • Oxidase — An oxidase is any enzyme that catalyzes an oxidation reduction reaction involving molecular oxygen (O2) as the electron acceptor. In these reactions, oxygen is reduced to water (H2O) or hydrogen peroxide (H2O2). The oxidases are a subclass of the …   Wikipedia

  • xanthine dehydrogenase — xan·thine de·hy·dro·gen·ase (zanґthēn de hiґdro jən ās) [EC 1.17.1.4] an enzyme of the oxidoreductase class that catalyzes the hydroxylation of xanthine to urate, using NAD+ as an electron acceptor; it also acts on a variety of… …   Medical dictionary

  • Xanthine — A substance found in caffeine, theobromine, and theophylline and encountered in tea, coffee, and the colas. Chemically, xanthine is a purine. There is a genetic disease of xanthine metabolism, xanthinuria, due to deficiency of an enzyme, xanthine …   Medical dictionary

  • Monoamine oxidase inhibitor — MAOI redirects here. For the Easter Island statues, see Moai. Monoamine oxidase Monoamine oxidase inhibitors (MAOIs) are a class of antidepressant drugs prescribed for the treatment of depression. They are particularly effective in treating… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”