citrulline n : an amino acid that does not occur in proteins but is an intermediate in the conversion of ornithine to arginine
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. 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.
BiosynthesisCitrulline 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 22.214.171.124). Arginine is first oxidized into N-hydroxyl-arginine, which is then further oxidized to citrulline concomitant with release of nitric oxide.
FunctionAlthough 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.
Dietary supplementCitrulline in the form of citrulline malate is sold as a performance-enhancing athletic dietary supplement which is said to reduce muscle fatigue. http://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=ShowDetailView&TermToSearch=12145119&ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum
citrulline in German: Citrullin
citrulline in Spanish: Citrulina
citrulline in French: Citrulline
citrulline in Italian: Citrullina
citrulline in Japanese: シトルリン
citrulline in Polish: Cytrulina
citrulline in Portuguese: Citrulina
citrulline in Russian: Цитруллин
citrulline in Swedish: Citrullin
citrulline in Ukrainian: Цитрулін
citrulline in Chinese: 瓜氨酸