Cyclooxygenase

cyclooxygenase 1
Crystallographic structure of prostaglandin H2 synthase-1 complex with flurbiprofen.
Identifiers
Symbol	PTGS1
Alt. symbols	COX-1
Entrez	5742
HUGO	9604
OMIM	176805
PDB	1CQE
RefSeq	NM_080591
UniProt	P23219
Other data
EC number	1.14.99.1
Locus	Chr. 9 q32-q33.3

cyclooxygenase 2
Cyclooxygenase-2 (Prostaglandin Synthase-2) in complex with a COX-2 selective inhibitor.
Identifiers
Symbol	PTGS2
Alt. symbols	COX-2
Entrez	5743
HUGO	9605
OMIM	600262
PDB	6COX
RefSeq	NM_000963
UniProt	P35354
Other data
EC number	1.14.99.1
Locus	Chr. 1 q25.2-25.3

Cyclooxygenase (COX), officially known as prostaglandin-endoperoxide synthase (PTGS), is an enzyme (specifically, a family of isozymes, EC 1.14.99.1) that is responsible for formation of prostanoids, including thromboxane and prostaglandins such as prostacyclin.

Pharmaceutical inhibition of COX can provide relief from the symptoms of inflammation and pain. Nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin and ibuprofen, exert their effects through inhibition of COX. Those that are specific to the COX-2 isozyme are called COX-2 inhibitors.

In medicine, the root symbol "COX" is encountered more often than "PTGS". In genetics, "PTGS" is officially used for this family of genes and proteins, because the root symbol "COX" was already used for the family. Thus the two isozymes found in humans, PTGS1 and PTGS2, are frequently called COX-1 and COX-2 in the medical literature. The names "prostaglandin synthase (PHS)", "prostaglandin synthetase (PHS)", and "prostaglandin-endoperoxide synthetase (PES)" are older terms still sometimes used to refer to COX.

In terms of their molecular biology, COX-1 and COX-2 are of similar molecular weight, approximately 70 and 72 kDa, respectively, and having 65% amino acid sequence homology and near-identical catalytic sites. The most significant difference between the isoenzymes, which allows for selective inhibition, is the substitution of isoleucine at position 523 in COX-1 with valine in COX-2. The smaller Val₅₂₃ residue in COX-2 allows access to a hydrophobic side-pocket in the enzyme (which Ile₅₂₃ sterically hinders). Drug molecules, such as DuP-697 and the coxibs derived from it, bind to this alternative site and are considered to be selective inhibitors of COX-2.