In enzymology, beta-carotene 15,15'-dioxygenase, (β-carotene 15,15'-dioxygenase) (EC1.13.11.63) is an enzyme with systematic namebeta-carotene:oxygen 15,15'-dioxygenase (bond-cleaving).[5][6] In human it is encoded by the BCO1 gene. This enzyme catalyses the following chemical reaction
beta-carotene + O2 → 2 all-trans-retinal
This is a cleavage reaction which cleaves β-carotene, utilizes molecular oxygen, is enhanced by the presence of bile salts and thyroxine, and generates two molecules of retinal. In humans, the enzyme is present in the small intestine and liver.[7] It can also cleave beta-cryptoxanthin, apocarotenal, , alpha-carotene and γ-carotene in decreasing order, all substrates greater than C30 with at least one unsubstituted β-ionone ring.[8]
This enzyme belongs to the (enzymatically-defined) family of oxidoreductases, specifically those acting on paired donors, with O2 as oxidant and incorporation or reduction of oxygen. Other names in common use include β-carotene 15,15'-monooxygenase and β-carotene dioxygenase. Its previous EC numbers include 1.13.11.21 (1975), 1.14.99.36 (2001).
In general, carnivores are poor converters of ionone-containing carotenoids, and pure carnivores such as felids (cats) lack 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.[9]
Beta-carotene 15,15'-dioxygenase belongs to the (similarity-defined) family of carotenoid oxygenases (InterPro: IPR004294). Enzymes of this family contain a Fe2+ active site, coordinated usually by four His residues.
^Kim YS, Park CS, Oh DK (July 2010). "Retinal production from beta-carotene by beta-carotene 15,15'-dioxygenase from an unculturable marine bacterium". Biotechnology Letters. 32 (7): 957–61. doi:10.1007/s10529-010-0239-3. PMID20229064. S2CID2347505.
Leuenberger MG, Engeloch-Jarret C, Woggon WD (2001). "The reaction mechanism of the enzyme-catalysed central cleavage of beta-carotene to retinal". Angew. Chem. 40 (14): 2614–2616. doi:10.1002/1521-3773(20010716)40:14<2613::aid-anie2613>3.0.co;2-z.