Cyclooxygenase (Cox) is also known as prostaglandin H synthase or PGH synthase (E.C. 18.104.22.168). It catalyzes the conversion of arachidonate to prostaglandin H2 (PGH2), the precursor of PGE2, PGF2α, PGD2, prostacyclin, and thromboxane A2. Cox actually has two different enzymatic activities: a cyclooxygenase that mediates the formation of PGG2 from oxygen and arachidonate and a hydroperoxidase that catalyzes a reduction of PGG2 yielding PGH2. Two Cox genes, Cox-1 and Cox-2, have been isolated in several species. A 4kb mRNA encodes the 604 amino acid Cox-2 protein. The two human Cox isoenzymes are 61% identical in amino acid composition with the active sites being highly conserved. Cox-2 mRNA and protein levels are induced by serum, lipopolysaccharides, growth factors, human chorionic gonadotropin and phorbol testers in various mammalian cell types. It has been shown that interleukin-1α (IL-1α) induces increased levels of Cox-2 mRNA and protein in human endothelial cells. The sustained increase in Cox-2 is apparently due (at least in part) to IL-1α increasing the stability of Cox-2 mRNA. This type of regulatory mechanism may play an important role in chronic inflammatory conditions.