enzymology, beta-carotene 15,15'-dioxygenase, ( EC 220.127.116.11) is an enzyme with systematic name beta-carotene:oxygen 15,15'-dioxygenase (bond-cleaving).  In human it is encoded by the BCDO2 gene. This enzyme  catalyses the following chemical reaction
beta-carotene + O 2 → 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. The dioxygenase also asymmetrically cleaves  beta-cryptoxanthin, , beta-4'-apo-β-carotenal, trans-β-apo-8'-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 ring.
This enzyme belongs to the (enzymatically-defined) family of
oxidoreductases, 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 oxygenases ( InterPro: ). Enzymes of this family contain a Fe IPR004294 2+ active site, coordinated usually by four His residues.
References [ edit ]
^ a b c
GRCh38: Ensembl release 89: ENSG00000135697 - Ensembl, May 2017
^ a b c
GRCm38: Ensembl release 89: ENSMUSG00000031845 - Ensembl, May 2017
"Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
"Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
Kim YS, Kim NH, Yeom SJ, Kim SW, Oh DK (June 2009). "In vitro characterization of a recombinant Blh protein from an uncultured marine bacterium as a beta-carotene 15,15'-dioxygenase". The Journal of Biological Chemistry. 284 (23): 15781–93. doi: . 10.1074/jbc.M109.002618 PMC . 2708875 PMID 19366683.
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. PMID 20229064. S2CID 2347505.
During A, Smith MK, Piper JB, Smith JC (November 2001). "beta-Carotene 15,15'-Dioxygenase activity in human tissues and cells: evidence of an iron dependency". The Journal of Nutritional Biochemistry. 12 (11): 640–647. doi: 10.1016/s0955-2863(01)00184-x. PMID 12031257.
Kim YS, Oh DK (March 2009). "Substrate specificity of a recombinant chicken beta-carotene 15,15'-monooxygenase that converts beta-carotene into retinal". Biotechnology Letters. 31 (3): 403–8. doi: 10.1007/s10529-008-9873-4. PMID 18979213. S2CID 21220270.
Wu L, Guo X, Wang W, Medeiros DM, Clarke SL, Lucas EA, Smith BJ, Lin D (November 2016). "Molecular aspects of β, β-carotene-9', 10'-oxygenase 2 in carotenoid metabolism and diseases". Exp Biol Med (Maywood). 241 (17): 1879–87. doi: 10.1177/1535370216657900. PMC . 5068469 PMID 27390265.
von Lintig J (November 2012). "Provitamin A metabolism and functions in mammalian biology". Am J Clin Nutr. 96 (5): 1234S–44S. doi: 10.3945/ajcn.112.034629. PMC . 3471205 PMID 23053549.
Green AS, Fascetti AJ (2016). "Meeting the Vitamin A Requirement: The Efficacy and Importance of β-Carotene in Animal Species". ScientificWorldJournal. 2016: 7393620. doi: 10.1155/2016/7393620. PMC . 5090096 PMID 27833936.