Xanthine

Xanthine is a product of purine catabolism. It is produced as a result of deamination of guanine (Figure 22.7) by guanine deaminase or by the reaction catalyzed by xanthine oxidase. These reactions are as follows:

> Guanine + H 2O <=> Xanthine + NH 3 (Guanine Deaminase)

> Hypoxanthine + O 2 <=> Xanthine + H 2O 2 (Xanthine Oxidase)

Xanthine oxidase can oxidize xanthine further to uric acid, as well (Figure 22.7)

Allopurinol, which is similar to hypoxanthine (see here), is used to treat gout because it inhibits xanthine oxidase, leading to accumulation of hypoxanthine and xanthine, both of which are more soluble and more readily excreted than uric acid (the causative agent of gout).

See also: Purine Degradation, Excessive Uric Acid in Purine Degradation