The enzyme 6-pyruvoyltetrahydropterin synthase catalyzes the following chemical reaction: 7,8-Dihydroneopterin 3′-triphosphate ⇌ {\displaystyle \rightleftharpoons } 6-pyruvoyltetrahydropterin + triphosphate This reaction is the second step in the biosynthesis of tetrahydrobiopterin from GTP, which is used as a cofactor in the synthesis of aromatic amino acid monooxygenases and nitric oxide synthase PTPS converts 7,8-dihydroneopterin triphosphate to 6-pyruvoyltetrahydropterin through the loss of the triphosphate group, a stereospecific reduction of the double bond between the top right nitrogen and carbon in the ring on the triphosphate on the right, the oxidation of the hydroxyl groups located on the first and second carbons of the side chain, and an internal base-catalyzed hydrogen transfer. Wikipedia