PGIS catalyzes the isomerization of PGH2 to PGI2. PGI2 (prostacyclin) is a potent vasodilator and inhibitor of platelet aggregation. PGIS is a membrane-bound hemoprotein localized primarily in endothelial cells.{3475} The cloned bovine and human enzymes contain 500 amino acids and a calculated molecular mass of 56,629 and 57,103, respectively.{3476,3477,3478} Northern blot analysis reveals that the mRNA for PGIS is expressed in a wide variety of human tissues and is particularly abundant in ovary, heart, skeletal muscle, lung, and prostate.{3476}