Protein-arginine deiminase

In enzymology, a protein-arginine deiminase is an enzyme that catalyzes a form of post translational modification called arginine de-imination or citrullination:


 * protein L -arginine + H2O $$\rightleftharpoons$$ protein L -citrulline + NH3

Thus, the two substrates of this enzyme are protein L -arginine (arginine residue inside a protein) and H2O, whereas its two products are protein  L -citrulline and NH3:


 * [[Image:citrullination.svg|300px|alt=The chemical conversion of arginine to citrulline, known as citrullination or deimination.]]

This enzyme belongs to the family of hydrolases, those acting on carbon-nitrogen bonds other than peptide bonds, specifically in linear amidines. The systematic name of this enzyme class is protein-L-arginine iminohydrolase. This enzyme is also called peptidylarginine deiminase.

Structural studies
As of late 2007, seven structures have been solved for this class of enzymes, with PDB accession codes, , , , , , and.

Mammalian proteins
Mammals have 5 protein-arginine deiminases, with symbols except for rodents, there the letter case is different: The different case is just a historical artifact. It doesn't indicate that the rodent proteins are special.
 * PADI1, PADI2, PADI3, PADI4, PADI6
 * Padi1, Padi2, Padi3, Padi4, Padi6