Phytoene () is a 40-carbon intermediate in the biosynthesis of
carotenoid
Carotenoids () are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, archaea, and fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips, corn, tomatoes, cana ...
s. The synthesis of phytoene is the first
committed step in the synthesis of carotenoids in
plants
Plants are the eukaryotes that form the kingdom Plantae; they are predominantly photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with cyanobacteria to produce sugars f ...
. Phytoene is produced from two molecules of
geranylgeranyl pyrophosphate
Geranylgeranyl pyrophosphate is an intermediate in the biosynthesis of diterpenes and diterpenoids. It is also the precursor to carotenoids, gibberellins, tocopherols, and chlorophylls.
It is also a precursor to geranylgeranylated proteins, whic ...
(GGPP) by the action of the enzyme
phytoene synthase
Phytoene synthase (, ''prephytoene-diphosphate synthase'', ''15-cis-phytoene synthase'', ''PSase'', ''geranylgeranyl-diphosphate geranylgeranyltransferase'') is a transferase enzyme involved in the biosynthesis of carotenoids. It catalyzes the con ...
. The two GGPP molecules are condensed together followed by removal of diphosphate and proton shift leading to the formation of phytoene.
Dietary phytoene and
phytofluene are found in a number of human tissues including the liver, lung, breast, prostate, colon, and skin. Accumulation of these carotenoids in the skin may protect the skin by several mechanisms: acting as
UV absorbers, as
antioxidants
Antioxidants are Chemical compound, compounds that inhibit Redox, oxidation, a chemical reaction that can produce Radical (chemistry), free radicals. Autoxidation leads to degradation of organic compounds, including living matter. Antioxidants ...
, and as anti-inflammatory agents.
Structure
Phytoene is a symmetric molecule containing three
conjugated double bonds. Phytoene has a UV-Vis absorption spectrum ''typical'' for a triply conjugated system with its main absorption maximum in the
UVB range at 286 nm and with ''
ε1% of 915''.
Sources
Analysis of several fruits and vegetables showed that phytoene and
phytofluene are found in majority of fruits and vegetables. In contrast to all other carotenoids, phytoene and phytofluene, the first carotenoid precursors in the biosynthetic pathway of other carotenoids, absorb light in the UV range.
History
The structure of phytoene was established and proven by total synthesis, by the
Basil Weedon group in 1966.
References
Further reading
*
{{carotenoids
Carotenoids
Tetraterpenes
Substances discovered in the 1960s