In enzymology, a pyrimidodiazepine synthase () is an enzyme that catalyzes the chemical reaction
The 3 substrates of this enzyme are pyrimidodiazepine, glutathione disulfide, and H<sub>2</sub>O, whereas its two products are 6-pyruvoyltetrahydropterin and glutathione.
This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-NH group of donors with a disulfide as acceptor. The systematic name of this enzyme class is pyrimidodiazepine:glutathione-disulfide oxidoreductase (ring-opening, cyclizing). Other names in common use include PDA synthase, pyrimidodiazepine:oxidized-glutathione oxidoreductase (ring-opening,, and cyclizing). This enzyme participates in glutathione metabolism.