Prostaglandin E2 (PGE2) is the most abundant prostanoid in the body and is a major mediator of inflammation in diseases such as osteoarthritis and rheumatoid arthritis. The product of arachidonic acid, prostaglandin H2 (PGH2) serves as the substrate for the isomerization to PGE2. The conversion is carried out by prostaglandin E synthases. Of the three forms, two are predominanly cytosolic. Prostaglandin E synthase 3 (PTGES3) is also called cytosolic prostaglandin E2 synthase (cPGES). Prostaglandin E synthase 2 (mPGES-2, PTGES2) is synthesized as a Golgi membrane-associated protein which undergoes a spontaneous cleavage of the N-terminal hydrophobic domain leading to a truncated mature cytosolic protein.