The Human Enzyme That Converts Dietary Provitamin A Carotenoids to Vitamin A Is a Dioxygenase |
| |
| Authors: | Carlo dela Se?a Kenneth M. Riedl Sureshbabu Narayanasamy Robert W. Curley Jr. Steven J. Schwartz Earl H. Harrison |
| |
| Affiliation: | From the ‡Department of Human Nutrition.;§Ohio State Biochemistry Program.;¶Department of Food Science and Technology, and ;‖College of Pharmacy, The Ohio State University, Columbus, Ohio 43210 |
| |
| 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 16O2-H218O or 18O2-H216O medium for 15 min at 37 °C, and the relative amounts of 18O-retinal and 16O-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 18O-retinal-H216O and 16O-retinal-H218O incubations to account for nonenzymatic oxygen exchange, our results show that BCO1 incorporates only oxygen from O2 into retinal. Thus, BCO1 is a dioxygenase. |
| |
| Keywords: | Carotenoid Dioxygenase Enzyme Catalysis Enzyme Mechanisms Oxidation-Reduction Retinoid Vitamin A Monooxygenase Oxygenase |
|
|
