Xanthine oxidoreductase

Xanthine oxidoreductase (XOR) is an enzyme that plays a crucial role in the purine metabolism pathway, specifically in the catabolism of purines. XOR is responsible for the oxidation of hypoxanthine to xanthine and can further catalyze the oxidation of xanthine to uric acid. This enzyme is a form of molybdenum-containing hydroxylase.

Structure

XOR is a large enzyme (approximately 290 kDa) that exists as a homodimer. Each monomer contains a molybdopterin cofactor, two iron-sulfur clusters, and a flavin adenine dinucleotide (FAD) domain. The molybdopterin cofactor is located in the molybdenum domain of the enzyme and is responsible for the enzyme's catalytic activity.

Function

The primary function of XOR is to catalyze the oxidation of hypoxanthine to xanthine and xanthine to uric acid. These reactions are part of the purine degradation pathway, which is important for the regulation of the levels of purine bases in the body. XOR also has a role in the production of reactive oxygen species, which can contribute to oxidative stress.

Clinical significance

Alterations in XOR activity have been associated with several pathological conditions. Increased XOR activity can lead to hyperuricemia and gout, due to the overproduction of uric acid. XOR inhibitors, such as allopurinol and febuxostat, are commonly used in the treatment of these conditions. XOR has also been implicated in the pathogenesis of cardiovascular diseases, as it can contribute to oxidative stress and inflammation.

See also

• Purine metabolism
• Gout
• Allopurinol
• Febuxostat