4-hydroxy-3-methylbut-2-en-1-yl Diphosphate Synthase

In enzymology, a 4-hydroxy-3-methylbut-2-en-1-yl diphosphate synthase (EC 1.17.7.1) is an enzyme that catalyzes the chemical reaction

(E)-4-hydroxy-3-methylbut-2-en-1-yl diphosphate + H₂O + protein-disulfide 2-C-methyl-D-erythritol 2,4-cyclodiphosphate + protein-dithiol

The 3 substrates of this enzyme are (E)-4-hydroxy-3-methylbut-2-en-1-yl diphosphate (HMB-PP), water, and protein disulfide, whereas its two products are 2-C-methyl-D-erythritol 2,4-cyclodiphosphate and protein dithiol.

This enzyme belongs to the family of oxidoreductases, specifically those acting on CH or CH₂ groups with a disulfide as acceptor. The systematic name of this enzyme class is (E)-4-hydroxy-3-methylbut-2-en-1-yl-diphosphate:protein-disulfide oxidoreductase (hydrating). This enzyme participates in biosynthesis of steroids.