Uric Acid (UA)

Uric acid is a diprotic acid with pKa₁=5.4 and pKa₂=10.3. Thus in strong alkali at high pH it forms the dually charged full urate ion, but at biological pH or in the presence of carbonic acid or carbonate ions it forms the singly charged hydrogen or acid urate ion as its pKa₂ is greater than the pKa₁ of carbonic acid. As its second ionization is so weak the full urate salts tend to hydrolyse back to hydrogen urate salts and free base at pH values around neutral. It is aromatic because of the purine functional group.

Uric acid is produced by xanthine oxidase from xanthine and hypoxanthine, which in turn are produced from purine. Uric acid is more toxic to tissues than either xanthine or hypoxanthine. Uric acid is released in hypoxic conditions.In humans and higher primates, uric acid is the final oxidation product of purine metabolism and is excreted in urine. In most other mammals, the enzyme uricase further oxidizes uric acid to allantoin.