Isomerase that catalyzes the conversion of PGH2 into the more stable prostaglandin E2 (PGE2) (in vitro) (PubMed:12804604, PubMed:18198127, PubMed:17585783). The biological function and the GSH-dependent property of PTGES2 is still under debate (PubMed:18198127, PubMed:17585783). In vivo, PTGES2 could form a complex with GSH and heme and would not participate in PGE2 synthesis but would catalyze the degradation of prostaglandin E2 H2 (PGH2) to 12(S)-hydroxy-5(Z),8(E),10(E)-heptadecatrienoic acid (HHT) and malondialdehyde (MDA) (PubMed:17585783) (By similarity). prostaglandin H2 = prostaglandin E2 prostaglandin H2 = (12S)-hydroxy-(5Z,8E,10E)-heptadecatrienoate + malonaldehyde Isomerase activity is increased by sulfhydril compounds. Dithiothreitol (DTT) is most effective, followed by dihydrolipoic acid, glutathione (GSH) and 2-mercaptoethanol. Lipid metabolism; prostaglandin biosynthesis. Homodimer. May interact with CEBPB (By similarity). Interacts with EXOSC10. Synthesized as a Golgi membrane-bound protein, which is further cleaved into the predominant soluble truncated form. The truncated form is cytoplasmic and is enriched in the perinuclear region. Widely expressed. Expressed in the heart, including apex, inter-ventricular septum, both atria and ventricles, but not in the aorta. Also expressed in fetal heart. Detected in various regions of the brain: cerebellum; occipital, frontal and parietal lobes. Also expressed in the lymph nodes, skeletal muscle, kidney and trachea, but not in the thymus or lung. Overexpressed in colorectal cancer. Synthesized as a Golgi membrane-associated protein, and the proteolytic removal of the N-terminal hydrophobic domain leads to the formation of a mature cytosolic enzyme. Belongs to the GST superfamily. It is not known if heme and GST are required for prostaglandin synthase activity. The protein copurifies with heme and GST when DTT is omitted during the purification procedure. The GSH-heme complex-bound enzyme has been proposed to act as a lyase and catalyze the degradation of prostaglandin E2 H2 (PGH2) to 12(S)-hydroxy-5(Z),8(E),10(E)-heptadecatrienoic acid (HHT) and malondialdehyde (MDA). According to PubMed:18198127, boiling the enzyme leads to loss of prostaglandin synthase activity, but does not eliminate the lyase activity. Besides, free heme can catalyze the formation of 12L-hydroxy-5,8,10-heptadecatrienoic acid (HHT) (PubMed:18198127). A more recent study demonstrates the GSH-dependent property of PTGES2, DTT dissociates the bound heme to produce active PGE2 synthase in vitro (By similarity). PTGES2 can only catalyzes PGE2 synthesis in the free state as an enzyme, while in vivo it forms a complex with heme and does not participate in PGE2 synthesis (By similarity). In agreement with this study, the in vivo evidence from PTGES2 deficient mice do not show that this protein is responsible for the PGE2 production under basal or pathophysiological conditions (By similarity).