Phytoene

Phytoene is a colorless tetraterpenoid and the first committed carotenoid in the biosynthesis pathway of photosynthetic organisms and some bacteria. It is synthesized from two molecules of geranylgeranyl pyrophosphate (GGPP) by the enzyme phytoene synthase (CrtB) to form a C40 carotene skeleton. Phytoene itself lacks visible color due to having relatively few conjugated double bonds. In plants and algae, phytoene is further desaturated by dedicated desaturases (phytoene desaturase and zeta-carotene desaturase) leading to color carotenoids such as phytofluene, zeta-carotene and lycopene. In many bacteria, a single desaturase (CrtI) can convert phytoene directly to lycopene, bypassing intermediates. The pathway eventually yields xanthophylls and other carotenoids that contribute to yellow to red pigmentation.

Phytoene is found in many photosynthetic tissues, seeds and fruits, often along with downstream carotenoids. It accumulates under certain genetic or environmental conditions when desaturation steps are limiting. Although phytoene itself is not a nutrient, its availability reflects carotenoid biosynthesis and is a precursor to compounds with photoprotective and antioxidant roles in plants.

Biotechnologists engineer phytoene synthase and downstream enzymes to alter carotenoid content in crops and microbial hosts. Phytoene measurement by chromatography is used in studies of carotenoid biosynthesis and regulation. In foods, carotenoid profiles including phytoene can influence color and nutritional value.