The citrulline is an alpha-amino acid and a key intermediate in the urea cycle. Its name is derived from citrullus, the Latin word for watermelon.
Several proteins contain citrulline as a result of a posttranslational. 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.