Aromatase's an enzyme that's responsible for a key step in the biosynthesis of estrogens. Because estrogens also promote certain cancers and other diseases, aromatase inhibitors are frequently used to treat those diseases. Steroids are composed of four fused rings (labeled A, B, C, and D in the figure below). Aromatase transforms the left-hand ring (the A-ring) of steroids to an aromatic state (hence the name) through oxidation and subsequent elimination of a methyl group. Aromatase's a member… (More on Aromatase)