Phytoene desaturase (zeta-carotene-forming) (EC 1.3.99.29, CrtIa, 2-step phytoene desaturase (ambiguous), two-step phytoene desaturase (ambiguous)) is an enzyme with systematic name 15-cis-phytoene:acceptor oxidoreductase (zeta-carotene-forming).^[1] This enzyme catalyses the following chemical reaction

15-cis-phytoene + 2 acceptor ${\displaystyle \rightleftharpoons }$ all-trans-zeta-carotene + 2 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

The enzyme is involved in carotenoid biosynthesis.

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