title: The human enzyme that converts dietary provitamin A carotenoids to vitamin A is a dioxygenase.
abstract: β-Carotene 15-15'-oxygenase (BCO1) catalyzes the oxidative cleavage of dietary provitamin A carotenoids to retinal (vitamin A aldehyde). Aldehydes readily exchange their carbonyl oxygen with water, making oxygen labeling experiments challenging. BCO1 has been thought to be a monooxygenase, incorporating oxygen from O2 and H2O into its cleavage products. This was based on a study that used conditions that favored oxygen exchange with water. We incubated purified recombinant human BCO1 and β-carotene in either (16)O2-H2(18)O or (18)O2-H2(16)O medium for 15 min at 37 °C, and the relative amounts of (18)O-retinal and (16)O-retinal were measured by liquid chromatography-tandem mass spectrometry. At least 79% of the retinal produced by the reaction has the same oxygen isotope as the O2 gas used. Together with the data from (18)O-retinal-H2(16)O and (16)O-retinal-H2(18)O incubations to account for nonenzymatic oxygen exchange, our results show that BCO1 incorporates only oxygen from O2 into retinal. Thus, BCO1 is a dioxygenase.
authors.affiliation: From the Department of Human Nutrition.
authors.forename: Carlo
authors.initials: C
authors.lastname: dela Seña
authors.forename: Kenneth M
authors.initials: KM
authors.lastname: Riedl
authors.forename: Sureshbabu
authors.initials: S
authors.lastname: Narayanasamy
authors.forename: Robert W
authors.initials: RW
authors.lastname: Curley
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Schwartz
authors.forename: Earl H
authors.initials: EH
authors.lastname: Harrison
mesh_terms: D049308:Dioxygenases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012172:Retinaldehyde / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D014801:Vitamin A / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics
chemical_list: D011994:Recombinant Proteins; D014801:Vitamin A; D049308:Dioxygenases; D012172:Retinaldehyde; D010100:Oxygen
keywords: Carotenoid; Dioxygenase; Enzyme Catalysis; Enzyme Mechanisms; Monooxygenase; Oxidation-Reduction; Oxygenase; Retinoid; Vitamin A