Urea cycle and metabolism of amino groups (Homo sapiens)

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32144Amino acid metabolismFumarate3.5.1.5GATMOAT3.5.2.14Citrate cycle (TCA cycle)CKBL-Citrulline2. and D-Ornithine metabolism(S)-1-Pyrroline-5-carboxylateASLCO2N2-Acetyl-L-ornithine6.3.4.6SpermidineFormate1.2.1.46N-(L-Arginino)succinateARG1Pyrimidine metabolismPhosphoguanidinoacetateL-glutamylSpermineNAGSCPS13.5.4.21Purine metabolism3. metabolismSMS2.6.1.11Proline metabolismPYCR1L-OrnithinePYCRLUrea-1-carboxylatePutrescineCarbamoylNH3GAMTSMS1.2.1.38ARG2CKMCreatinineAlanine and aspartate metabolismASSGlutamate metabolismSRMCreatineSarcosinecreatine-PUreaL-Aspartate1.5.99.1GLUD1N-Acetyl-L-glutamateN-CarbamoylsarcosineL-Glutamate 5-semialdehyde3.5.1.543.5.1.59ALDH18A1N-MethylhydantoinN-Acetyl-glutamateArginine metabolismODC1ArginineN-Acetyl-L-glutamate


The urea cycle (also known as the ornithine cycle) is a cycle of biochemical reactions that produces urea ((NH2)2CO) from ammonia (NH3). This cycle occurs in ureotelic organisms. The urea cycle converts highly toxic ammonia to urea for excretion. This cycle was the first metabolic cycle to be discovered (Hans Krebs and Kurt Henseleit, 1932), five years before the discovery of the TCA cycle. The urea cycle takes place primarily in the liver and, to a lesser extent, in the kidneys.

Amino acid catabolism results in waste ammonia. All animals need a way to excrete this product. Most aquatic organisms, or ammonotelic organisms, excrete ammonia without converting it. Ammonia is toxic, but upon excretion from aquatic species, it is diluted by the water outside the organism. Organisms that cannot easily and safely remove nitrogen as ammonia convert it to a less toxic substance such as urea or uric acid. The urea cycle mainly occurs in the liver. The urea produced by the liver is then released into the bloodstream where it travels to the kidneys and is ultimately excreted in urine. In species including birds and most insects, the ammonia is converted into uric acid or its urate salt, which is excreted in solid form.

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Ontology Terms



  1. Dahlman, Douglas L., Milan A. Berge.; ''Possible mechanisms for adverse effects of L-canavanine on insects.''; ACS Publications, 1986
  2. Seiler N; ''Ornithine aminotransferase, a potential target for the treatment of hyperammonemias.''; Curr Drug Targets, 2000 PubMed
  3. Deuschle K, Funck D, Hellmann H, Däschner K, Binder S, Frommer WB; ''A nuclear gene encoding mitochondrial Delta-pyrroline-5-carboxylate dehydrogenase and its potential role in protection from proline toxicity.''; Plant J, 2001 PubMed
  4. Dahlman, Douglas L., Milan A. Berge.; ''Possible mechanisms for adverse effects of L-canavanine on insects.''; , 1986


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103837view12:35, 10 April 2019IreneHemelAdded Uniprot IDs
103836view11:00, 10 April 2019IreneHemelChanged datanodes for enzymes from geneproduct to protein
96019view15:13, 15 February 2018Mkutmonremoved old pathways attributes
96018view15:13, 15 February 2018MkutmonModified description
95281view18:12, 29 November 2017DeSlChanged several graphical lines to directed interactions + added litertaure references for these.
94180view13:40, 25 August 2017DeSlAdded ID for L-Glutamyl
92933view09:00, 20 July 2017EgonwFixed to the correct CAS number: it had the number of creatine.
72142view10:02, 25 October 2013Mkutmonadded datasource to EC numbers
71261view21:34, 16 October 2013MaintBotAutomated update of data sources
71169view11:01, 11 October 2013Mkutmonfixed unconnected lines
68976view17:41, 8 July 2013MaintBotUpdated to 2013 gpml schema
45014view18:23, 6 October 2011KhanspersOntology Term : 'urea cycle pathway' added !
43586view14:08, 5 July 2011AdrienDefayadd database name for TCA
41149view23:40, 1 March 2011MaintBotRemoved redundant pathway information and comments
38842view17:40, 24 September 2010Khanspers
38688view18:15, 23 September 2010KhanspersMore pathway links
38687view18:08, 23 September 2010KhanspersAdded pathway links and changed arrows and layout
38685view18:04, 23 September 2010KhanspersPeriodical save, work in progress
34435view18:15, 10 December 2009MaintBotAutomatic update of empty xrefs
32123view13:53, 14 August 2009MaintBotFixed group labels
21724view11:32, 14 November 2008MaintBot[[Pathway:Homo sapiens:Urea cycle and metabolism of amino groups KEGG]] moved to [[Pathway:WP497]]: Moved to stable identifier
13997view16:08, 20 May 2008Thomasconnected lines
13129view11:18, 17 May 2008MaintBotautomated metabolite conversion
8476view13:46, 7 January 2008MaintBot[[Pathway:Human:Urea cycle and metabolism of amino groups KEGG]] moved to [[Pathway:Homo sapiens:Urea cycle and metabolism of amino groups KEGG]]: Renaming species
7854view16:23, 18 December 2007MaintBotfixed category names
7413view12:42, 4 November 2007MaintBotAdded categories to GPML
6404view22:18, 22 May 2007L.M.Ferrantegpml file for [[Human:Urea_cycle_and_metabolism_of_amino_groups_KEGG]]

External references


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NameTypeDatabase referenceComment
(S)-1-Pyrroline-5-carboxylateMetaboliteC03912 (KEGG Compound) Tautomer of L-glutamate 5-semialdehyde (Enzyme Nomenclature) (Enzyme Nomenclature) (Enzyme Nomenclature) (Enzyme Nomenclature) (Enzyme Nomenclature) (Enzyme Nomenclature) (Enzyme Nomenclature) (Enzyme Nomenclature) (Enzyme Nomenclature) (Enzyme Nomenclature) (Enzyme Nomenclature) (Enzyme Nomenclature) (Enzyme Nomenclature) (Enzyme Nomenclature) (Enzyme Nomenclature) (Enzyme Nomenclature) (Enzyme Nomenclature)
ACY1GeneProduct95 (Entrez Gene)
ALDH18A1GeneProduct5832 (Entrez Gene)
ARG1GeneProduct383 (Entrez Gene)
ARG2GeneProduct384 (Entrez Gene)
ASLGeneProduct435 (Entrez Gene)
ASSGeneProduct445 (Entrez Gene)
Alanine and aspartate metabolismPathwayWP106 (WikiPathways)
Amino acid metabolismPathway
Arginine metabolismPathway
ArginineMetabolite74-79-3 (CAS) L-Arginine
CKBGeneProduct1152 (Entrez Gene)
CKMGeneProduct1158 (Entrez Gene)
CO2MetaboliteC00011 (KEGG Compound)
CPS1GeneProduct1373 (Entrez Gene)
CarbamoylMetaboliteC00169 (KEGG Compound)
Citrate cycle (TCA cycle)PathwayWP78 (WikiPathways)
CreatineMetabolite57-00-1 (CAS) Creatine
CreatinineMetabolite60-27-5 (CAS) Creatinine
D-Arginine and D-Ornithine metabolismPathway
FormaldehydeMetabolite50-00-0 (CAS) Formaldehyde
FormateMetaboliteC00058 (KEGG Compound)
FumarateMetaboliteC00122 (KEGG Compound)
GAMTGeneProduct2593 (Entrez Gene)
GATMGeneProduct2628 (Entrez Gene)
GLUD1GeneProduct2746 (Entrez Gene)
Glutamate metabolismPathway
GuanidinoacetateMetaboliteC00581 (KEGG Compound)
L-AspartateMetaboliteC00049 (KEGG Compound)
L-CitrullineMetabolite372-75-8 (CAS) L-Citrulline
L-Glutamate 5-semialdehydeMetaboliteC01165 (KEGG Compound) tautomer of (S)-1-Pyrroline-5-carboxylate
L-GlutamateMetabolite56-86-0 (CAS) L-Glutamate
L-OrnithineMetabolite70-26-8 (CAS) L-Ornithine
L-ProlineMetabolite147-85-3 (CAS) L-Proline
L-glutamylMetaboliteCHEBI:29972 (ChEBI)
N-(L-Arginino)succinateMetaboliteC03406 (KEGG Compound)
N-Acetyl-L-glutamateMetaboliteC00624 (KEGG Compound)
N-Acetyl-glutamateMetaboliteC00624 (KEGG Compound)
N-CarbamoylsarcosineMetaboliteC01043 (KEGG Compound)
N-MethylhydantoinMetaboliteC02565 (KEGG Compound)
N2-Acetyl-L-ornithineMetaboliteC00437 (KEGG Compound)
NAGSGeneProduct162417 (Entrez Gene)
NH3MetaboliteC00014 (KEGG Compound)
Nitrogen metabolism Pathway
OATGeneProduct4942 (Entrez Gene)
ODC1GeneProduct4953 (Entrez Gene)
OTCGeneProduct5009 (Entrez Gene)
PYCR1GeneProduct5831 (Entrez Gene)
PYCRLGeneProduct65263 (Entrez Gene)
PhosphoguanidinoacetateMetaboliteC03166 (KEGG Compound)
Proline metabolismPathway
Purine metabolismPathway
PutrescineMetabolite110-60-1 (CAS) Putrescine
Pyrimidine metabolismPathway
SMSGeneProduct6611 (Entrez Gene)
SRMGeneProduct6723 (Entrez Gene)
SarcosineMetabolite107-97-1 (CAS) Sarcosine
SpermidineMetabolite124-20-9 (CAS) Spermidine
SpermineMetabolite71-44-3 (CAS) Spermine
Urea-1-carboxylateMetaboliteC01010 (KEGG Compound)
UreaMetabolite57-13-6 (CAS) Urea
creatine-PMetabolite67-07-2 (CAS) Phosphocreatine

Annotated Interactions

No annotated interactions

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