In
enzymology
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
, beta-carotene 15,15'-dioxygenase, () is an
enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
with
systematic name A systematic name is a name given in a systematic way to one unique group, organism, object or chemical substance, out of a specific population or collection. Systematic names are usually part of a nomenclature.
A semisystematic name or semitrivial ...
''beta-carotene:oxygen 15,15'-dioxygenase (bond-cleaving)''. In human it is encoded by the BCDO2 gene. 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 ...
:
beta-carotene + O
2 → 2
all-trans-retinal
Retinal (also known as retinaldehyde) is a polyene chromophore. Retinal, bound to proteins called opsins, is the chemical basis of visual phototransduction, the light-detection stage of visual perception (vision).
Some microorganisms use retin ...
This is a cleavage reaction which cleaves
β-carotene
β-Carotene is an organic, strongly coloured red-orange pigment abundant in fungi, plants, and fruits. It is a member of the carotenes, which are terpenoids (isoprenoids), synthesized biochemically from eight isoprene units and thus having 40 ...
, utilizes molecular oxygen, is enhanced by the presence of
bile salts
Bile acids are steroid acids found predominantly in the bile of mammals and other vertebrates. Diverse bile acids are synthesized in the liver. Bile acids are conjugated with taurine or glycine residues to give anions called bile salts.
Primary b ...
and
thyroxine
File:Thyroid_system.svg, upright=1.5, The thyroid system of the thyroid hormones T3 and T4
rect 376 268 820 433 Thyroid-stimulating hormone
rect 411 200 849 266 Thyrotropin-releasing hormone
rect 297 168 502 200 Hypothalamus
rect 66 216 386 25 ...
, and generates two molecules of
retinal
Retinal (also known as retinaldehyde) is a polyene chromophore. Retinal, bound to proteins called opsins, is the chemical basis of visual phototransduction, the light-detection stage of visual perception (vision).
Some microorganisms use retin ...
. In humans, the enzyme is present in the small intestine and liver. The dioxygenase also asymmetrically cleaves
beta-cryptoxanthin,
''trans''-β-apo-8'-carotenal, beta-4'-apo-β-carotenal,
alpha-carotene and
gamma-carotene in decreasing order, creating one retinal molecule, all of these being substrates with a carbon chain greater than C
30, with at least one unsubstituted
β-ionone
The ionones are a series of closely related chemical substances that are part of a group of compounds known as rose ketones, which also includes damascones and damascenones. Ionones are aroma compounds found in a variety of essential oils, inc ...
ring.
This enzyme belongs to the (enzymatically-defined) family of
oxidoreductase
In biochemistry, an oxidoreductase is an enzyme that catalyzes the transfer of electrons from one molecule, the reductant, also called the electron donor, to another, the oxidant, also called the electron acceptor. This group of enzymes usually ut ...
s, specifically those acting on paired donors, with O
2 as oxidant and incorporation or reduction of oxygen. A related enzyme is β-carotene 15,15'-monooxygenase, coded for by the gene BCMO1, which symmetrically cleaves β-carotene into two retinal molecules.
In general, carnivores are poor converters of ionone-containing carotenoids, and pure carnivores such as felids (cats) lack beta-carotene 15,15'-dioxygenase and beta-carotene 15,15'-monooxygenase and cannot convert any carotenoids to retinal, resulting in none of the carotenoids being forms of vitamin A for these species. They must have preformed vitamin A in their diet.
Beta-carotene 15,15'-dioxygenase belongs to the (similarity-defined) family of
carotenoid oxygenase __NOTOC__
Carotenoid oxygenases are a Protein family, family of enzymes involved in the Bond cleavage, cleavage of carotenoids to produce, for example, retinol, commonly known as vitamin A. This family includes an enzyme known as RPE65 which is a ...
s (). Enzymes of this family contain a Fe
2+ active site, coordinated usually by four His residues.
References
EC 1.13.11
Iron enzymes
Enzymes of unknown structure
{{1.13-enzyme-stub