In enzymology, a protein-arginine deiminase (PAD) () is an enzyme that catalyzes a form of post translational modification called arginine de-imination or citrullination:
Thus, the two substrates of this enzyme are protein <small>L</small>-arginine (arginine residue inside a protein) and H<sub>2</sub>O, whereas its two products are protein <small>L</small>-citrulline and NH<sub>3</sub>:
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.
As of late 2007, seven structures have been solved for this class of enzymes, with PDB accession codes , , , , , , and .
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.
Irreversible inhibitors
Reversible inhibitors