All-trans-zeta-carotene desaturase (, Crtlb, phytoene desaturase (ambiguous), 2-step phytoene desaturase (ambiguous), two-step phytoene desaturase (ambiguous), CrtI (ambiguous)) is an enzyme with systematic name all-trans-zeta-carotene:acceptor oxidoreductase. This enzyme catalyses the following chemical reaction
This enzyme is involved in carotenoid biosynthesis.