Xanthine oxidase

Xanthine oxidase (XO) is a type of enzyme that plays a crucial role in the metabolism of purines in the human body. It is a form of oxidoreductase that catalyzes the oxidation of hypoxanthine to xanthine and can further catalyze the oxidation of xanthine to uric acid. These reactions are a part of the degradation pathway of purines in the body.

Structure

Xanthine oxidase is a large enzyme whose active site consists of a molybdenum atom, two iron atoms, and two sulfur atoms. The molybdenum atom is coordinated to the enzyme via a cysteine residue and two oxo groups. The iron atoms are part of a ferrous center, which is involved in the transfer of electrons during the catalytic cycle.

Function

The primary function of xanthine oxidase is to catalyze the oxidation of hypoxanthine to xanthine and then to uric acid. This is a key step in the catabolism of purines in the body. The enzyme also has a role in the metabolism of certain drugs, such as allopurinol, which is used to treat gout.

Clinical significance

Xanthine oxidase has been implicated in several diseases. In gout, the overproduction of uric acid by xanthine oxidase leads to the accumulation of uric acid crystals in the joints, causing inflammation and pain. In cardiovascular disease, xanthine oxidase has been shown to contribute to oxidative stress, which can damage the heart and blood vessels.

Inhibition

Several drugs are used to inhibit the activity of xanthine oxidase, including allopurinol and febuxostat. These drugs are used to treat gout and other conditions associated with high levels of uric acid.

See also

• Purine metabolism
• Gout
• Allopurinol
• Febuxostat