prostaglandin-endoperoxide synthase 2 prostaglandin-endoperoxide synthase 2 prostaglandin-endoperoxide synthase 2 (prostaglandin g/h synthase and cyclooxygenase) (the hugo official symbol is ptgs2; hgnc id, hgnc:9605), also known as cyclooxygenase-2 or cox-2, is an enzyme that in humans is encoded by the ptgs2 gene. in humans it is one of two cyclooxygenases. it is involved in the conversion of arachidonic acid to prostaglandin h2, an important precursor of prostacyclin, which is expressed in inflammation.