Phytoene desaturase (lycopene-forming) (CrtI, ''four-step phytoene desaturase'') (, ''15-cis-phytoene:acceptor oxidoreductase (lycopene-forming)'') are

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

s found in

archaea Archaea ( ) is a Domain (biology), domain of organisms. Traditionally, Archaea only included its Prokaryote, prokaryotic members, but this has since been found to be paraphyletic, as eukaryotes are known to have evolved from archaea. Even thou ...

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

and

fungi A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...

that are involved in

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 ...

biosynthesis. They catalyze the conversion of colorless 15-''cis''-phytoene into a bright red

lycopene Lycopene is an organic compound classified as a tetraterpene and a carotene. Lycopene (from the Neo-Latin '' Lycopersicon'', the name of a former tomato genus) is a bright red carotenoid hydrocarbon found in tomatoes and other red fruits and ve ...

in a biochemical pathway called the poly-trans pathway. The same process in plants and

cyanobacteria Cyanobacteria ( ) are a group of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" () refers to their bluish green (cyan) color, which forms the basis of cyanobacteri ...

utilizes four separate enzymes in a poly-''cis'' pathway.

Biochemistry

Bacterial phytoene desaturases were shown to require FAD as a cofactor for their function. During the

chemical reaction A chemical reaction is a process that leads to the chemistry, chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an Gibbs free energy, ...

in total four additional

double bonds In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betwee ...

are introduced into phytoene: : 15-''cis''-phytoene + 4 acceptor

\rightleftharpoons

all-''trans''-lycopene + 4 reduced acceptor (overall reaction) : (1a) 15-''cis''-phytoene + acceptor

\rightleftharpoons

all-''trans''-phytofluene + reduced acceptor : (1b) all-''trans''-phytofluene + acceptor

\rightleftharpoons

all-''trans''-''zeta''-carotene + reduced acceptor : (1c) all-''trans''-''zeta''-carotene + acceptor

\rightleftharpoons

all-''trans''-neurosporene + reduced acceptor: : (1d) all-''trans''-neurosporene + acceptor

\rightleftharpoons

all-''trans''-lycopene + reduced acceptor

Applications

In 2000 it was discovered that the

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

insertion of a bacterial phytoene desaturase into transgenic tomatoes increased the lycopene content without the need to alter several of the plants enzymes. This approach was later used in

rice Rice is a cereal grain and in its Domestication, domesticated form is the staple food of over half of the world's population, particularly in Asia and Africa. Rice is the seed of the grass species ''Oryza sativa'' (Asian rice)—or, much l ...

to increase its β-carotene content resulting in the

Golden Rice Golden rice is a variety of rice ('' Oryza sativa'') produced through genetic engineering to biosynthesize beta-carotene, a precursor of vitamin A, in the edible parts of the rice. It is intended to produce a fortified food to be grown and ...

project.

References

External links

* {{Portal bar, Biology, border=no EC 1.3.99

Biochemistry

Applications

See also

References

External links