In enzymology, 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 substrate (chemistry), substrates, and the enzyme converts the substrates into different molecule ...

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 chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and break ...

: beta-carotene + O₂ → 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, utilizes molecular oxygen, is enhanced by the presence of bile salts 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 38 ...

, 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 re ...

. 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 C₃₀, with at least one unsubstituted β-ionone 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 ...

s, specifically those acting on paired donors, with O₂ 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 oxygenases (). Enzymes of this family contain a Fe²⁺ active site, coordinated usually by four His residues.

References

EC 1.13.11 Iron enzymes Enzymes of unknown structure {{1.13-enzyme-stub