Citrulline

Citrulline
IUPAC name 2-Amino-5-(carbamoylamino)pentanoic acid
Identifiers
CAS number	372-75-8 Y
PubChem	9750
ChemSpider	9367 Y
UNII	29VT07BGDA Y
DrugBank	DB00155
KEGG	D07706 Y
ChEBI	CHEBI:16349 Y
ChEMBL	CHEMBL444814 Y
IUPHAR ligand	722
Jmol-3D images	Image 1
SMILES O=C(O)[C@@H](N)CCCNC(=O)N
InChI InChI=1S/C6H13N3O3/c7-4(5(10)11)2-1-3-9-6(8)12/h4H,1-3,7H2,(H,10,11)(H3,8,9,12)/t4-/m0/s1 Y Key: RHGKLRLOHDJJDR-BYPYZUCNSA-N Y InChI=1/C6H13N3O3/c7-4(5(10)11)2-1-3-9-6(8)12/h4H,1-3,7H2,(H,10,11)(H3,8,9,12)/t4-/m0/s1 Key: RHGKLRLOHDJJDR-BYPYZUCNBX
Properties
Molecular formula	C6H13N3O3
Molar mass	175.19 g mol−1
Y (verify) (what is: Y/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.

Biosynthesis

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 1.14.13.39).^[2] Arginine is first oxidized into N-hydroxyl-arginine, which is then further oxidized to citrulline concomitant with release of nitric oxide.

Function

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]

Sources

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

• Citrullinemia

References

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. http://www.clinchem.org/cgi/content/full/53/3/498. 
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. http://bjsm.bmj.com/cgi/pmidlookup?view=long&pmid=12145119. 
6. ^ Watermelon May Have Viagra-effect