Urea is the end product of protein metabolism (amino acid metabolism). The nitrogen of amino acids, converted to ammonia, is toxic to the body. It is converted to urea and detoxified. As such, urea accounts for 80–90% of the nitrogen containing substances excreted in urine.
Urea is synthesized in liver and transported to kidneys for excretion in urine.
Urea cycle is the first metabolic cycle that was elucidated by Hans Krebs and Kurt Henseleit (1932), hence it is known as Krebs-Henseleit cycle. The individual reactions, however, were described in more detail later on by Ratner and Cohen.
Urea has two amino (−NH2) groups, one derived from NH3 and the other from aspartate. Carbon atom is supplied by CO2. Urea synthesis is a five-step cyclic process, with five distinct enzymes. The first two enzymes are present in mitochondria while the rest are localized in cytosol.
Outline of urea cycle
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| Basics of Urea cycle |
Note : In the synthesis of urea one amino group comes from ammonium ion while the other is from aspartate; carbon is derived from CO2.
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