Phytoene desaturase (neurosporene-forming) (EC 1.3.99.28, 3-step phytoene desaturase, three-step phytoene desaturase, phytoene desaturase (ambiguous), CrtI (ambiguous)) is an enzyme with systematic name 15-cis-phytoene:acceptor oxidoreductase (neurosporene-forming).^[1][2] This enzyme catalyses the following chemical reaction

15-cis-phytoene + 3 acceptor ${\displaystyle \rightleftharpoons }$ all-trans-neurosporene + 3 reduced acceptor (overall reaction)

(1a) 15-cis-phytoene + acceptor ${\displaystyle \rightleftharpoons }$ all-trans-phytofluene + reduced acceptor

(1b) all-trans-phytofluene + acceptor ${\displaystyle \rightleftharpoons }$ all-trans-zeta-carotene + reduced acceptor

(1c) all-trans-zeta-carotene + acceptor ${\displaystyle \rightleftharpoons }$ all-trans-neurosporene + reduced acceptor

This enzyme is involved in carotenoid biosynthesis.

• Phytoene desaturase (lycopene-forming)
• 15-Cis-phytoene desaturase
• Phytoene desaturase (zeta-carotene-forming)
• Phytoene desaturase (3,4-didehydrolycopene-forming)