CAS number 372-75-8 YesY
PubChem 9750
ChemSpider 9367 YesY
DrugBank DB00155
KEGG D07706 YesY
ChEBI CHEBI:16349 YesY
IUPHAR ligand 722
Jmol-3D images Image 1
Molecular formula C6H13N3O3
Molar mass 175.19 g mol−1
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

The organic compound citrulline is an α-amino acid. Its name is derived from citrullus, the Latin word for watermelon, from which it was first isolated in 1930.[1] It has the idealized formula H2NC(O)NH(CH2)3CH(NH2)CO2H. It is a key intermediate in the urea cycle, the pathway by which mammals excrete ammonia.



Citrulline is made from ornithine and carbamoyl phosphate in one of the central reactions in the urea cycle. It is also produced from arginine as a by-product of the reaction catalyzed by NOS family (NOS; EC[2] Arginine is first oxidized into N-hydroxyl-arginine, which is then further oxidized to citrulline concomitant with release of nitric oxide.


Although citrulline is not coded for by DNA directly, several proteins are known to contain citrulline as a result of a posttranslational modification. These citrulline residues are generated by a family of enzymes called peptidylarginine deiminases (PADs), which convert arginine into citrulline in a process called citrullination or deimination. Proteins that normally contain citrulline residues include myelin basic protein (MBP), filaggrin, and several histone proteins, whereas other proteins, such as fibrin and vimentin are susceptible to citrullination during cell death and tissue inflammation.

Patients with rheumatoid arthritis often have detectable antibodies against proteins containing citrulline. Although the origin of this immune response is not known, detection of antibodies reactive with citrulline (anti-citrullinated protein antibodies) containing proteins or peptides is now becoming an important help in the diagnosis of rheumatoid arthritis.[3]

In recent studies, citrulline has been found to relax blood vessels.[4]


Citrulline in the form of citrulline malate is sold as a performance-enhancing athletic dietary supplement, which was shown to reduce muscle fatigue in a preliminary clinical trial.[5]

The rind of watermelon (Citrullus lanatus) is a good natural source of citrulline.[6]

See also


  1. ^ Wada, M (1930). "Über Citrullin, eine neue Aminosäure im Presssaft der Wassermelone, Citrullus vulgaris Schrad.". Biochem. Zeit. 224: 420. 
  2. ^ Cox M, Lehninger AL, Nelson DR (2000). Lehninger principles of biochemistry (3rd ed.). New York: Worth Publishers. ISBN 1-57259-153-6. 
  3. ^ Coenen D, Verschueren P, Westhovens R, Bossuyt X (March 2007). "Technical and diagnostic performance of 6 assays for the measurement of citrullinated protein/peptide antibodies in the diagnosis of rheumatoid arthritis". Clin. Chem. 53 (3): 498–504. doi:10.1373/clinchem.2006.078063. PMID 17259232. 
  4. ^ Viagra-Like Effects From Watermelon
  5. ^ Bendahan D, Mattei JP, Ghattas B, Confort-Gouny S, Le Guern ME, Cozzone PJ (Aug 2002). "Citrulline/malate promotes aerobic energy production in human exercising muscle". Br J Sports Med 36 (4): 282–9. doi:10.1136/bjsm.36.4.282. PMC 1724533. PMID 12145119. 
  6. ^ Watermelon May Have Viagra-effect

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  • citrulline — n. an amino acid that is an intermediate in the conversion of ornithine to arginine. [WordNet 1.5] …   The Collaborative International Dictionary of English

  • citrulline — citrulline. См. цитруллин. (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.

  • Citrulline — La citrulline est un acide aminé (C6H13N3O3). Cet acide aminé n est pas codé par le code génétique dans l ADN. À ce titre, il n entre pas dans la composition des protéines. C est le principal produit de l action de l ornithine transcarbamylase… …   Wikipédia en Français

  • citrulline — (= 2 amino 5 ureiodovaleric acid) An a amino acid not found in proteins. L citrulline is an intermediate in the urea cycle …   Dictionary of molecular biology

  • citrulline — citrulinas statusas T sritis chemija formulė H₂NCONH(CH₂)₃CH(NH₂)COOH atitikmenys: angl. citrulline rus. цитруллин ryšiai: sinonimas – 2 amino 5 ureidopentano rūgštis …   Chemijos terminų aiškinamasis žodynas

  • citrulline — noun Etymology: International Scientific Vocabulary, from New Latin Citrullus, genus name of the watermelon Date: 1930 a crystalline amino acid C6H13N3O3 formed especially as an intermediate in the conversion of ornithine to arginine …   New Collegiate Dictionary

  • citrulline — /si treuh leen /, n. Biochem. an amino acid, NH2CONH(CH2)3CHNH2COOH, abundant in watermelons and an intermediate compound in the urea cycle. [1930; < NL citrull(us) the watermelon genus (ML citrul(l)us, citrolus, Latinization of South It citrulo …   Universalium

  • citrulline — noun An amino acid, first isolated from watermelons, that is an intermediate in the urea cycle …   Wiktionary

  • citrulline — N5 (Aminocarbonyl) l ornithine; α amino δ ureidovaleric; 5 ureidonorvaline; an amino acid formed from l ornithine in the course of the urea cycle as well as a product in nitric oxide biosynthesis; also found in watermelon (Citrullus vulgaris) and …   Medical dictionary

  • citrulline — ci·trul·line …   English syllables