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. Because the "COX" term is used for the stem symbol for "cytochrome c oxidase" family of genes and gene products including proteins, the "PTGS" symbol is used for the prostaglandin-endoperoxide synthase (cyclooxygenase) family of genes and proteins. It is involved in the conversion of arachidonic acid to prostaglandin H2, an important precursor of prostacyclin and thromboxane A2, among others.