Uricotelic organisms

Excess nitrogen is excreted as ammonia. Ammonotelic organisms excrete ammonia directly, uricotelic organisms excrete it as uric acid, and ureotelic organisms excrete it as urea. 

Uric acid, the major nitrogenous waste product of uricotelic organisms, is also formed in other organisms from the breakdown of purine bases. Gout is caused by the deposition of excess uric acid crystals in the joints. 

Uric acid (Fig. 6) is the main nitrogenous waste product of uricotelic organisms (reptiles, birds and insects), but is also formed in ureotelic organisms from the breakdown of the purine bases from DNA and RNA (see Topics FI and Gl). Some individuals have a high serum level of sodium urate (the predominant form of uric acid at neutral pH) which can lead to crystals of this compound being deposited in the joints and kidneys, a condition known as gout, a type of arthritis characterized by extremely painful joints. 

Uric acid, 2,6,S-trihydroxypmnu an excretory product of purine metabolism in most animals. In some animals, known as uricotelic organisms (birds, reptiles, many insects), it is the main nitrogenous excretory product. U.a. (Af, 168.1, m.p. 400°C) was discovered in urine in 1776 by Scheele, and it can be isolated in quantity from bird excrements (guano) its salts are called urates Humans and the great apes usually excrete U. a. unchanged. In the adult human, 1-3 % of urinary nitrogen is represented by U.a. 

In terms of amino nitrogen excretion the animal kingdom can be classified into ammonotelic (ammonia), ureotelic (urea) and uricotelic (uric acid) organisms depending on the nature of the discharged substance. 

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