Editing Citrulline (section)

==Function==
Citrulline is a metabolic intermediate within the [[urea cycle]], which is the pathway by which mammals excrete ammonia by converting it into urea. Citrulline is also produced as a byproduct of the enzymatic production of nitric oxide from the amino acid arginine, catalyzed by nitric oxide synthase. In the yeast species Saccharomyces cerevisiae, citrulline is a metabolic intermediate in the latter, cytosolic half of the arginine biosynthesis pathway.<ref>{{cite web | url=https://pathway.yeastgenome.org/YEAST/new-image?object=CITRUL-BIO2-PWY | title=Saccharomyces cerevisiae citrulline biosynthesis }}</ref>

Several proteins contain citrulline as a result of a [[post-translational modification]]. These citrulline residues are generated by a family of enzymes called [[peptidylarginine deiminase]]s (PADs), which convert arginine into citrulline in a process called [[citrullination]] or deimination with the help of calcium ions. 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]].

Circulating citrulline concentration is a [[biomarker]] of intestinal functionality.<ref>{{Cite journal|last1=Fragkos|first1=Konstantinos C.|last2=Forbes|first2=Alastair|date=2017-10-12|title=Citrulline as a marker of intestinal function and absorption in clinical settings: A systematic review and meta-analysis|journal=United European Gastroenterology Journal|volume=6|issue=2|pages=181–191|language=en|doi=10.1177/2050640617737632|pmid=29511548|pmc=5833233}}</ref><ref>{{cite journal | last1 = Crenn | first1 = P. | display-authors = etal   | year = 2000 | title = Post-absorptive plasma citrulline concentration is a marker of intestinal failure in short bowel syndrome patients | journal = Gastroenterology | volume = 119 | issue = 6| pages = 1496–505 | doi=10.1053/gast.2000.20227| pmid = 11113071 | doi-access = free }}</ref>