Arachidonic acid (AA) is a 20 carbon unsaturated fatty acid which is present in the lipid bilayer of all mammalian cells. AA is released from the membrane by phospholipases, thus making it available for conversion to bioactive lipids. The cyclooxygenase pathway is one of three pathways (the others being lipoxygenase and P450 monooxygenase pathways) that perform this conversion.\n\nThe enzyme that acts in the cyclooxygenase pathway is called cyclooxygenase (COX) or prostaglandin H synthase (PGHS). PGHS exhibits a dual catalytic activity, a cyclooxygenase and a peroxidase. The cyclooxygenase catalyzes the initial conversion of AA to an intermediate, prostaglandin G2 (PGG2) whilst the peroxidase converts PGG2 to prostaglandin H2 (PGH2) via a two-electron reduction. PGH2 is the intermediate for products that play critical roles in immune function regulation, kidney development and mucosal integrity of the GI tract.\n\nPGHS exists in two isoforms, 1 and 2 and both forms can perform the above reactions. Form 1 is constitutively expressed in most tissues and is involved in performing normal physiological functions. Form 2, in contrast, is inducible and is involved in critical steps of rheumatic disease, inflammation and tumorigenesis.