Sepiapterin reductase (L threo 7,8 dihydrobiopterin forming)

Sepiapterin reductase (L-threo-7,8-dihydrobiopterin forming) (EC 1.1.1.325) is an enzyme with systematic name L-threo-7,8-dihydrobiopterin:NADP⁺ oxidoreductase. This enzyme catalyses the following chemical reaction

(1) L-threo-7,8-dihydrobiopterin + NADP⁺ ⇌ sepiapterin + NADPH + H⁺ (2) L-threo-tetrahydrobiopterin + 2 NADP⁺ ⇌ 6-pyruvoyl-5,6,7,8-tetrahydropterin + 2 NADPH + 2 H⁺

This bacterial (Chlorobium tepidum) enzyme catalyses the final step in the de novo synthesis of tetrahydrobiopterin from GTP.