Carotenoid Oxygenase
Encyclopedia
Carotenoid oxygenases are a family
of enzyme
s involved in the cleavage
of carotenoid
s to produce, for example, retinol
, commonly known as vitamin A
. This family includes a receptor which is abundantly expressed in retinal pigment epithelium, and binds plasma retinal binding protein.
Carotenoids such as beta-carotene
, lycopene
, lutein
and beta-cryptoxanthine are produced in plants and certain bacteria, algae and fungi, where they function as accessory photosynthetic pigments and as scavengers of oxygen radicals for photoprotection
. They are also essential dietary nutrients in animals. Carotenoid oxygenases cleave a variety of carotenoids into a range of biologically important products, including apocarotenoid
s in plants that function as hormone
s, pigments, flavours, floral scents and defence compounds, and retinoids in animals that function as vitamin
s, visual pigments and signalling molecules. Examples of carotenoid oxygenases include:
Protein family
A protein family is a group of evolutionarily-related proteins, and is often nearly synonymous with gene family. The term protein family should not be confused with family as it is used in taxonomy....
of enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
s involved in the cleavage
Cleavage
Cleavage may refer to:*Cleavage , partial exposure of the separation between a woman's breasts.**Cleavage enhancement, methods of making a person's breast cleavage look more substantial than it really is....
of carotenoid
Carotenoid
Carotenoids are tetraterpenoid organic pigments that are naturally occurring in the chloroplasts and chromoplasts of plants and some other photosynthetic organisms like algae, some bacteria, and some types of fungus. Carotenoids can be synthesized fats and other basic organic metabolic building...
s to produce, for example, retinol
Retinol
Retinol is one of the animal forms of vitamin A. It is a diterpenoid and an alcohol. It is convertible to other forms of vitamin A, and the retinyl ester derivative of the alcohol serves as the storage form of the vitamin in animals....
, commonly known as vitamin A
Vitamin A
Vitamin A is a vitamin that is needed by the retina of the eye in the form of a specific metabolite, the light-absorbing molecule retinal, that is necessary for both low-light and color vision...
. This family includes a receptor which is abundantly expressed in retinal pigment epithelium, and binds plasma retinal binding protein.
Carotenoids such as beta-carotene
Beta-carotene
β-Carotene is a strongly-coloured red-orange pigment abundant in plants and fruits. It is an organic compound and chemically is classified as a hydrocarbon and specifically as a terpenoid , reflecting its derivation from isoprene units...
, lycopene
Lycopene
Lycopene is a bright red carotene and carotenoid pigment and phytochemical found in tomatoes and other red fruits and vegetables, such as red carrots, watermelons and papayas...
, lutein
Lutein
Lutein is a xanthophyll and one of 600 known naturally occurring carotenoids. Lutein is synthesized only by plants and like other xanthophylls is found in high quantities in green leafy vegetables such as spinach and kale...
and beta-cryptoxanthine are produced in plants and certain bacteria, algae and fungi, where they function as accessory photosynthetic pigments and as scavengers of oxygen radicals for photoprotection
Photoprotection
Photoprotection is a group of mechanisms that nature has developed to minimize the damage that the human body suffers when exposed to UV radiation...
. They are also essential dietary nutrients in animals. Carotenoid oxygenases cleave a variety of carotenoids into a range of biologically important products, including apocarotenoid
Apocarotenoid
Apocarotenoids are organic compounds which occur widely in living organisms. They are derived from carotenoids by oxidative cleavage,catalyzed by carotenoid oxygenases. Examples include the vitamin A retinoids retinal, retinoic acid, and retinol; and the plant hormone abscisic acid....
s in plants that function as hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
s, pigments, flavours, floral scents and defence compounds, and retinoids in animals that function as vitamin
Vitamin
A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. In other words, an organic chemical compound is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on...
s, visual pigments and signalling molecules. Examples of carotenoid oxygenases include:
- Beta-carotene 15,15'-monooxygenaseBeta-carotene 15,15'-monooxygenaseIn enzymology, a beta-carotene 15,15'-monooxygenase is an enzyme that catalyzes the chemical reactionThus, the two substrates of this enzyme are beta-carotene and O2, whereas its product is retinal....
(BCDO1; ) from animals, which cleaves beta-carotene symmetrically at the central double bond to yield two molecules of retinal. - Beta-carotene-9',10'-dioxygenase (BCDO2) from animals, which cleaves beta-carotene asymmetrically to apo-10'-beta-carotenal and beta-ionone, the latter being converted to retinoic acid. Lycopene is also oxidatively cleaved.
- 9-cis-epoxycarotenoid dioxygenase from plants, which cleaves 9-cis xanthophylls to xanthoxinXanthoxinXanthoxin is an intermediate in the biosynthesis of the plant hormone abscisic acid....
, a precursor of the hormone abscisic acid. - Apocarotenoid-15,15'-oxygenase from bacteria and cyanobacteria, which converts beta-apocarotenals rather than beta-carotene into retinal. This protein has a seven-bladed beta-propeller structure with four hisitidines that hold the iron active centre.
- Retinal pigment RPE65 from animals, which in its soluble form binds all-trans retinol, and in its membrane-bound form binds all-trans retinyl esters. RPE65 is important for the production of 11-cis retinal during visual pigment regeneration.