Cyclooxygenase catalyzes the first step in the biosynthesis of prostaglandins, thromboxanes, and prostacyclins: the conversion of arachidonic acid to prostaglandin H2 COX-1 is constitutively expressed in almost all animal tissues and is involved in the homeostatic role of eicosanoids. Recent discoveries of the induction of cyclooxygenase biosynthesis by a variety of stimuli such as phorbol esters, lipopolysaccharides, and cytokines led to the hypothesis that the inducible form of cyclooxygenase, COX-2, is responsible for the biosynthesis of prostaglandins under acute inflammatory conditions. COX-1 and -2 are 70 and 72 kDa proteins, respectively. Both cyclooxygenases have been cloned from a variety of species including human, mouse, rat, and sheep. COX-1 isoform at the amino acid level, whereas the homology between COX-1 and COX-2 is only about 60%.
