| align=right | 160 |- | Calcium dihydrogen diurate | align=right | 603 | align=right | 276 |- | Disodium urate | align=right | 77 | align=center | — |- | Dipotassium urate | align=right | 44 | align=right | 35 |- | Calcium urate | align=right | 1,500 | align=right | 1,440 |- | Strontium urate | align=right | 4,300 | align=right | 1,790 |- | Barium urate | align=right | 7,900 | align=right | 2,700 |} The figures given indicate what mass of water is required to dissolve a unit mass of compound indicated. The lower the number, the more soluble the substance in the said solvent. Biochemistry Xanthine oxidase (found in mammals primarily as xanthine dehydrogenase and rarely as an oxidase) is an enzyme which catalyzes the formation of uric acid from xanthine and hypoxanthine, which in turn are produced from other purines. Xanthine oxidase is a large enzyme whose active site consists of the metal molybdenum bound to sulfur and oxygen. Within cells, xanthine oxidase can exist as xanthine dehydrogenase and xanthine oxireductase, which has also been purified from bovine milk and spleen extracts. Uric acid is released in hypoxic conditions (low oxygen saturation). Genetic and physiological diversity Primates In humans and other great apes, uric acid (actually hydrogen urate ion) is the final oxidation (breakdown) product of purine metabolism and is excreted in urine, whereas in most other mammals, the enzyme uricase further oxidizes uric acid to allantoin. The loss of uricase in higher primates parallels the similar loss of the ability to synthesize ascorbic acid, leading to the suggestion that urate may partially substitute for ascorbate in such species. Both uric acid and ascorbic acid are strong reducing agents (electron donors) and potent antioxidants. In humans, over half the antioxidant capacity of blood plasma comes from hydrogen urate ion. Humans The normal concentration range of uric acid (or hydrogen urate ion) in human blood is 25 to 80 mg/L for men and 15 to 60 mg/L for women (but see below for slightly different values). An individual can have serum values as high as 96 mg/L and not have gout. In humans, about 70% of daily uric acid disposal occurs via the kidneys, and in 5–25% of humans, impaired renal (kidney) excretion leads to hyperuricemia. Normal excretion of uric acid in the urine is 270 to 360 mg per day (concentration of 270 to