Phytoene desaturase (lycopene-forming)
Crystallographic structure of a bacterial phytoene desaturase monomer from Pantoea ananatis.[1]
Identifiers
EC no.	1.3.99.31
Databases
IntEnz	IntEnz view
BRENDA	BRENDA entry
ExPASy	NiceZyme view
KEGG	KEGG entry
MetaCyc	metabolic pathway
PRIAM	profile
PDB structures	RCSB PDB PDBe PDBsum
Search PMC articles PubMed articles NCBI proteins

Phytoene desaturase (lycopene-forming) (CrtI, four-step phytoene desaturase) (EC 1.3.99.31, 15-cis-phytoene:acceptor oxidoreductase (lycopene-forming)) are enzymes found in archaea, bacteria and fungi that are involved in carotenoid biosynthesis.^[2] They catalyze the conversion of colorless 15-cis-phytoene into a bright red lycopene in a biochemical pathway called the poly-trans pathway. The same process in plants and cyanobacteria utilizes four separate enzymes in a poly-cis pathway.^[3]

Biochemistry

Bacterial phytoene desaturases were shown to require FAD as a cofactor for their function.^[4] During the chemical reaction in total four additional double bonds are introduced into phytoene:

15-cis-phytoene + 4 acceptor ${\displaystyle \rightleftharpoons }$ all-trans-lycopene + 4 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

(1c) all-trans-zeta-carotene + acceptor ${\displaystyle \rightleftharpoons }$ all-trans-neurosporene + reduced acceptor:

(1d) all-trans-neurosporene + acceptor ${\displaystyle \rightleftharpoons }$ all-trans-lycopene + reduced acceptor

Applications

In 2000 it was discovered that the gene insertion of a bacterial phytoene desaturase into transgenic tomatoes increased the lycopene content without the need to alter several of the plants enzymes.^[5] This approach was later used in rice to increase its β-carotene content resulting in the Golden Rice project.