Aromatase

(CC) Image: David E. Volk
Human placental aromatase bound to ligands androstenedione (cyan) and heme (yellow). Coordinates obtained by the RCSB Protein Data Bank (3EQM)

Aromatase is an enzyme that removes the C-19 methyl group and oxidizes the 3- and 17-positions of steroids, including reactions that convert androgenic steroids (testosterone) into estrogenic steroids (estrogen). Because some tumors are estrogen-sensitive, aromatase inhibitors are sometimes used to treat cancer, mostly in post-menopausal women because aromatase inhibitors do not block estrogen synthesis in the ovaries.