Ornithine transcarbamylase

Ornithine transcarbamylase
Ornithine carbamoyltransferase

Human OTC trimer. From PDB 1OTH.
Symbols OTC; MGC129967; MGC129968; MGC138856; OCTD
External IDs OMIM300461 MGI97448 HomoloGene446 GeneCards: OTC Gene
EC number
RNA expression pattern
PBB GE OTC 207200 at tn.png
More reference expression data
Species Human Mouse
Entrez 5009 18416
Ensembl ENSG00000036473 ENSMUSG00000031173
UniProt P00480 Q543H3
RefSeq (mRNA) NM_000531.5 NM_008769.3
RefSeq (protein) NP_000522.3 NP_032795.1
Location (UCSC) Chr X:
38.21 – 38.28 Mb
Chr X:
9.83 – 9.9 Mb
PubMed search [1] [2]

Ornithine transcarbamoylase (OTC) (also called ornithine carbamoyltransferase) is an enzyme that catalyzes the reaction between carbamoyl phosphate (CP) and ornithine (Orn) to form citrulline (Cit) and phosphate (Pi). In plants and microbes, OTC is involved in arginine (Arg) biosynthesis, whereas in mammals it is located in the mitochondria and is part of the urea cycle.



OTC is a trimer. The monomer unit has a CP-binding domain and an amino acid-binding domain. Each of the two discrete substrate-binding domains (SBDs) have an α/β topology with a central β-pleated sheet embedded in flanking α-helices.

The active sites are located at the interface between the protein monomers.


The reaction mechanism of OTC.
The side-chain amino group of Orn attacks the carbonyl carbon of CP nucleophilically, left, to form a tetrahedral transition state, middle. Charge rearrangement releases Cit and Pi, right. [1]


OTC monomer

If a person is deficient in OTC, ammonia levels will build up, and this will cause neurological problems. Levels of the amino acids, glutamate, and alanine will be increased (as these are the amino acids that receive nitrogen from others).

Levels of urea cycle intermediates may be decreased, as carbamoyl phosphate cannot replenish the cycle. The carbamoyl phosphate instead goes into the uridine monophosphate synthetic pathway. Here orotic acid (one step of this alternative pathway) levels in the blood are increased.

A potential treatment for the high ammonia levels is to give sodium benzoate, which combines with glycine to produce hippurate, at the same time removing an ammonium group.


  1. a Free text.png Mechanism of inactivation of ornithine transcarbamoylase by Ndelta -(N'-Sulfodiaminophosphinyl)-L-ornithine, a true transition state analogue? Crystal structure and implications for catalytic mechanism. J Biol Chem. 2000 Jun 30; 275: 20012-9; PubMed Free text

Further reading

External links

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Look at other dictionaries:

  • Ornithine transcarbamylase — Ornithine carbamoyltransférase L ornithine carbamoyltransférase (ou ornithine transcarbamylase, ou encore OTC) est une enzyme catalysant la réaction de carbamoylation de l ornithine en citrulline et inversement. Structure L OTC se présente sous… …   Wikipédia en Français

  • ornithine transcarbamylase — n an enzyme of hepatic mitochondria that catalyzes the conversion of ornithine to citrulline as part of urea formation and that when deficient in the body results in hyperammonemia, vomiting, coma, seizures, and sometimes death called also… …   Medical dictionary

  • ornithine transcarbamylase — ornithine transcarbamylase. См. орнитинтранскарбамилаза. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • Ornithine transcarbamylase deficiency — Classification and external resources Ornithine ICD 10 E …   Wikipedia

  • ornithine transcarbamylase deficiency — noun A rare genetic metabolic disorder of the urea cycle. Abbreviated as OTC. See Also: ornithine transcarbamylase …   Wiktionary

  • ornithine transcarbamylase — noun An enzyme that catalyzes the reaction between carbamoyl phosphate and ornithine to form citrulline and phosphate. Syn: ornithine carbamoyltransferase …   Wiktionary

  • Déficit en ornithine transcarbamylase — Déficit en ornithine carbamyl transférase Déficit en ornithine carbamyl transférase Autre nom Déficit en ornithine transcarbamylase (OTC) Référence MIM …   Wikipédia en Français

  • ornithine transcarbamylase deficiency — X linked disorder, the most common cause of inherited urea cycle disorders …   Dictionary of molecular biology

  • Ornithine transcarbamylase (OTC) deficiency — A rare metabolic disorder, OTC is one of the urea cycle disorders. The urea cycle is a series of five liver enzymes that help rid the body of ammonia, a toxic breakdown product of protein. When one of these enzymes is missing or deficient,… …   Medical dictionary

  • Ornithine translocase deficiency — Classification and external resources Ornithine ICD 9 …   Wikipedia

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