enzymology Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...

, a protein-arginine deiminase () is an

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...

that

catalyzes Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

a form of

post translational modification Post-translational modification (PTM) is the covalent and generally enzymatic modification of proteins following protein biosynthesis. This process occurs in the endoplasmic reticulum and the golgi apparatus. Proteins are synthesized by ribosome ...

called arginine de-imination or

citrullination Citrullination or deimination is the conversion of the amino acid arginine in a protein into the amino acid citrulline. Citrulline is not one of the 20 standard amino acids encoded by DNA in the genetic code. Instead, it is the result of a post-tr ...

: :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: : This enzyme belongs to the family of hydrolases, those acting on carbon-nitrogen bonds other than

peptide bond In organic chemistry, a peptide bond is an amide type of covalent chemical bond linking two consecutive alpha-amino acids from C1 (carbon number one) of one alpha-amino acid and N2 (nitrogen number two) of another, along a peptide or protein cha ...

s, 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 *

PADI1 Peptidyl arginine deiminase, type I, also known as PADI1, is a protein which in humans is encoded by the ''PADI1'' gene. This gene encodes a member of the peptidyl arginine deiminase family of enzymes, which catalyze the post-translational deimi ...

PADI2 Protein-arginine deiminase type-2 is an enzyme that in humans is encoded by the ''PADI2'' gene. This gene encodes a member of the peptidyl arginine deiminase family of enzymes, which catalyze the post- translational deimination of proteins by c ...

PADI3 Peptidyl arginine deiminase, type III, also known as PADI3, is a protein which in humans is encoded by the ''PADI3'' gene. This gene encodes a member of the peptidyl arginine deiminase family of enzymes, which catalyze the post-translational dei ...

PADI4 Protein-arginine deiminase type-4, is a human protein which in humans is encoded by the ''PADI4'' gene. The protein as an enzyme, specifically protein-arginine deiminase, a type of hydrolase. Molecular biology The human gene is found on the shor ...

, PADI6 except for

rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are na ...

s, there the letter case is different: *Padi1, Padi2, Padi3, Padi4, Padi6 The different case is just a historical artifact. It doesn't indicate that the rodent proteins are special.

References

* * EC 3.5.3 Enzymes of known structure {{3.5-enzyme-stub