Citrulline

Citrulline

Names
IUPAC name 2-Amino-5-(carbamoylamino)pentanoic acid
Identifiers
CAS Number	627-77-0 N 13594-51-9 R N 372-75-8 S N
3DMet	B01217
Beilstein Reference	1725417, 1725415 R, 1725416 S
ChEBI	CHEBI:18211 N
ChEMBL	ChEMBL444814 Y
ChemSpider	810 N 553200 R N 9367 S N
DrugBank	DB00155 Y
EC Number	211-012-2
Gmelin Reference	774677 S
IUPHAR/BPS	722
Jmol 3D model	Interactive image Interactive image
KEGG	D07706 Y
MeSH	Citrulline
PubChem	833 637599 R 9750 S
UNII	29VT07BGDA Y
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) N Key: RHGKLRLOHDJJDR-UHFFFAOYSA-N N
SMILES NC(CCCNC(N)=O)C(O)=O NC(CCC[nH]:c(:[nH2]):[o])c(:[o]):[oH]
Properties
Chemical formula	C6H13N3O3
Molar mass	175.19 g·mol−1
Appearance	White crystals
Odor	Odourless
log P	−1.373
Acidity (pKa)	2.508
Basicity (pKb)	11.489
Thermochemistry
Specific heat capacity (C)	232.80 J K−1 mol−1
Std molar entropy (So298)	254.4 J K−1 mol−1
Related compounds
Related alkanoic acids	N-Acetylaspartic acid Aceglutamide N-Acetylglutamic acid Pivagabine
Related compounds	Bromisoval Carbromal
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
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 1914 by Koga & Odake. It was finally identified by Wada in 1930. It has the formula H₂NC(O)NH(CH₂)₃CH(NH₂)CO₂H. It is a key intermediate in the urea cycle, the pathway by which mammals excrete ammonia.

In the body, citrulline is produced as a byproduct of the enzymatic production of nitric oxide from the amino acid arginine, catalyzed by nitric oxide synthase. This is an essential reaction in the body because nitric oxide is an important vasodilator required for regulating blood pressure.

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). It is made from arginine by the enzyme trichohyalin at the inner root sheath and medulla of hair follicles. Arginine is first oxidized into N-hydroxyl-arginine, which is then further oxidized to citrulline concomitant with release of nitric oxide.

Function

Several proteins 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.

Circulating citrulline concentration is, in humans, a biomarker of intestinal functionality.

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 human study.

The rind of watermelon (Citrullus lanatus) is a natural source of citrulline, discussed in one report as a precursor to producing nitric oxide which is a physiological factor in relaxing vascular smooth muscle and erectile organs.

See also

• Citrullinemia