|1725417, 1725415 R, 1725416 S|
|Molar mass||175.19 g·mol−1|
|232.80 J K−1 mol−1|
|254.4 J K−1 mol−1|
Related alkanoic acids
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
|what is: / ?)(|
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.
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 18.104.22.168). 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.
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.
The rind of watermelon (Citrullus lanatus) is a good natural source of citrulline, discussed in one report as a dietary precursor to producing nitric oxide which is a physiological factor in relaxing smooth muscle in blood vessels and erectile organs.
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