[7][8] There are two isozymes of COX encoded by distinct gene products: a constitutive COX-1 (this enzyme) and an inducible COX-2, which differ in their regulation of expression and tissue distribution.

A splice variant of COX-1 termed COX-3 was identified in the central nervous system of dogs, but does not result in a functional protein in humans.

It converts free arachidonic acid, released from membrane phospholipids at the sn-2 ester binding site by the enzymatic activity of phospholipase A2, to prostaglandin (PG) H2.

Metabolism of arachidonic acid forms a labile intermediate peroxide, PGG2, which is reduced to the corresponding alcohol, PGH2, by the enzyme's hydroperoxidase activity.

[11] The two 15-HETE stereoisomers have intrinsic biological activities but, perhaps more importantly, can be further metabolized to a major class of anti-inflammatory agents, the lipoxins.