In enzymology, a prostaglandin-D synthase (EC 5.3.99.2) is an enzyme that catalyzes the chemical reaction.

This enzyme belongs to the family of isomerases, specifically a class of other intramolecular oxidoreductases.

In March 2012, American scientists reported a discovery that shows this enzyme triggers male baldness.

[1] According to the discovery, levels of this enzyme are elevated in the cells of hair follicles located in bald patches on the scalp, but not in hairy areas.

As of late 2001, 7 structures have been solved for this class of enzymes, with PDB accession codes 1IYH, 1IYI, 1PD2, 1V40, 2CZT, 2CZU, and 2E4J.