Uric acid is an organic compound of carbon, nitrogen, oxygen and hydrogen with the structure shown right:

xanthine oxidase oxidizes oxypurines such as xanthine and hypoxanthine to uric acid. In humans and higher primates, uric acid is the final oxidation product of purine metabolism. 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 vitamin C. This may be because uric acid partially replaces ascorbic acid (another strong reducing substance) in primate metabolism.

Uric acid is also the end product of nitrogen metabolism in birds and reptiles. In such species, it is excreted in feces as a dry mass. While this compound is produced through a complex and energetically costly metabolic pathway (in comparison to other nitrogenated wastes such as urea or ammonia), its elimination minimizes water loss. It is therefore commonly found in the excretions of animals that live in very dry environments.

Humans produce only small quantities of uric acid with excess accumulation leading to a type of arthritis known as gout.

In human blood, uric acid concentrations between 3.6 and 8.3 mg/dL are considered normal by the American Medical Association, although significantly lower levels are common in vegetarians due to a decreased intake of purine-rich meat.

The disease gout in humans is associated with abnormal levels of uric acid in the system. Saturation of uric acid in the human blood stream may result in one form of kidney stones when the acid crystallizes into solid inside the kidney. A percentage of gout patients eventually get uric kidney stones.

Uric acid may be a marker of oxidative stress, and may have a potential therapeutic role as an antioxidant (PMID 16375736). On the other hand, like other strong reducing substances such as ascorbate, uric acid can also act as a proxidant, particularly at elevated levels. Thus, as noted here, it is unclear whether elevated levels of uric acid in diseases associated with oxidative stress such as stroke and atherosclerosis are a reactive protective response or a primary cause.

The high nitrogen content of uric acid makes guano a useful agricultural fertilizer.

The crystalline form of uric acid is used as a reflector in certain species of fireflies.

See also

• Hyperuricemia

External links

• MedlinePlus - Uric Acid Test

External links

Amides | Nitrogen metabolism

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