Phytoene synthase (, ''prephytoene-diphosphate synthase'', ''15-cis-phytoene synthase'', ''PSase'', ''geranylgeranyl-diphosphate geranylgeranyltransferase'') is a
transferase
A transferase is any one of a class of enzymes that catalyse the transfer of specific functional groups (e.g. a methyl or glycosyl group) from one molecule (called the donor) to another (called the acceptor). They are involved in hundreds of ...
enzyme involved in the biosynthesis of
carotenoids. It catalyzes the conversion of
geranylgeranyl pyrophosphate
Geranylgeranyl pyrophosphate is an intermediate in the biosynthesis of diterpenes and di terpenoids. It is also the precursor to carotenoids, gibberellins, tocopherols, and chlorophylls.
It is also a precursor to geranylgeranylated proteins, wh ...
to
phytoene
Phytoene () is a 40-carbon intermediate in the biosynthesis of carotenoids. The synthesis of phytoene is the first committed step in the synthesis of carotenoids in plants. Phytoene is produced from two molecules of geranylgeranyl pyrophosphate (G ...
.
This enzyme
catalyses the following
chemical reaction
A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...
: 2
geranylgeranyl diphosphate 15-cis-phytoene + 2
diphosphate
In chemistry, pyrophosphates are phosphorus oxyanions that contain two phosphorus atoms in a P–O–P linkage. A number of pyrophosphate salts exist, such as disodium pyrophosphate (Na2H2P2O7) and tetrasodium pyrophosphate (Na4P2O7), among othe ...
(overall reaction)
:(1a) 2 geranylgeranyl diphosphate
diphosphate +
prephytoene diphosphate
Prephytoene diphosphate is a carotenoid precursor.
{{Cholesterol and steroid intermediates
Carotenoids
Organophosphates
Cyclopropanes ...
:(1b) prephytoene diphosphate
15-cis-phytoene + diphosphate
This enzyme requires Mn
2+ for activity. It belongs to
squalene/phytoene synthase family
The squalene/phytoene synthase family represents proteins that catalyze the head-to-head condensation of C15 and C20 prenyl units (i.e. farnesyl diphosphate and genranylgeranyl diphosphate). This enzymatic step constitutes part of steroid and c ...
of proteins.
References
EC 2.5.1
{{2.5-enzyme-stub