urea cycle

biochemistry

Also known as: Krebs-Henseleit cycle

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Last updated

July 14, 2026

Quick Summary

The urea cycle is a biochemical process occurring in the liver that converts toxic ammonia, a byproduct of amino acid breakdown, into urea. Urea is a less toxic compound that can be excreted from the body in urine.1

This cycle is essential for nitrogenous waste disposal in mammals. When amino acids are metabolized, ammonia is released. The urea cycle then incorporates this ammonia into urea through a series of enzyme-catalyzed reactions.21

Defects in any of the enzymes involved in the urea cycle can lead to a dangerous buildup of ammonia in the blood, a condition known as hyperammonemia. This can cause severe health problems, including lethargy, vomiting, and coma, particularly in newborns. Urea cycle disorders are typically inherited in an autosomal recessive pattern, with one exception being ornithine transcarbamylase (OTC) deficiency, which is X-linked.1

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Sir Hans Adolf Krebs
…reactions (now known as the urea cycle) by which ammonia is converted to urea in mammalian tissue; the urea, far less toxic than ammonia, is subsequently excreted in the urine of most mammals. This cycle also serves as a major source of the amino acid arginine.
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…reactions (now known as the urea cycle) by which ammonia is converted to urea in mammalian tissue; the urea, far less toxic than ammonia, is subsequently excreted in the urine of most mammals. This cycle also serves as a major source of the amino acid arginine.
Read More