This is a family of bacterial and archaeal proteins that catalyses or regulates the conversion of beta-carotene to retinal [1]. Characterisation of BCD proteins shows them to cleave beta-carotene at its central double bond (15,15') to yield two molecules of all-trans-retinal. However, the oxygen atom of retinal originated not from water but from molecular oxygen, suggesting that the enzyme was a beta-carotene 15,15'-dioxygenase, rather than a mono-oxygenase that catalyses the same biochemical reaction [2,3].

1: brp and blh are required for synthesis of the retinal cofactor of bacteriorhodopsin in Halobacterium salinarum. Peck RF, Echavarri-Erasun C, Johnson EA, Ng WV, Kennedy SP, Hood L, DasSarma S, Krebs MP; J Biol Chem. 2001;276:5739-5744. PMID:11092896

2: In vitro characterization of a recombinant Blh protein from an uncultured marine\tbacterium as a beta-carotene 15,15'-dioxygenase. Kim YS, Kim NH, Yeom SJ, Kim SW, Oh DK; J Biol Chem. 2009;284:15781-15793. PMID:19366683

3: Retinal production from beta-carotene by beta-carotene 15,15'-dioxygenase from an unculturable marine bacterium. Kim YS, Park CS, Oh DK; Biotechnol Lett. 2010;32:957-961. PMID:20229064