Bifunctional enzyme which catalyzes both the conversion of PGH2 to PGD2, a prostaglandin involved in smooth muscle contraction/relaxation and a potent inhibitor of platelet aggregation, and the conjugation of glutathione with a wide range of aryl halides, organic isothiocyanates and alpha,beta-unsaturated carbonyls. Also exhibits low glutathione-peroxidase activity towards cumene hydroperoxide and t-butyl hydroperoxide. prostaglandin H2 = prostaglandin D2 glutathione + RX = a halide anion + an S-substituted glutathione + H(+) 2-glyceryl-prostaglandin H2 = 2-glyceryl-prostaglandin D2 Glutathione is required for the prostaglandin D synthase activity. Highly expressed in liver, kidney, small intestine and colon, moderately in pancreas, bone marrow, lung and ovary, and expressed at low levels in spleen, thymus, heart and brain. Not detected in oviduct or skin (at protein level) (PubMed:9657971). Expressed in liver (PubMed:11572089). Significantly increased expression by estrogen. Up-regulated after 1 hour of exposure to estrogen. Expression persists through 72 hours. Belongs to the GST superfamily. Sigma family.