Abstract
The 2-O-α-d-glucoside of l-ascorbic acid (AA-2G) is a highly stabilized form of vitamin C, with important industrial applications in cosmetics, food, and pharmaceuticals. AA-2G is currently produced through biocatalytic glucosylation of l-ascorbic acid from starch-derived oligosaccharides. Sucrose would be an ideal substrate for AA-2G synthesis, but it lacks a suitable transglycosidase. We show here that in a narrow pH window (pH 4.8–6.0, with sharp optimum at pH 5.2), sucrose phosphorylases catalyzed the 2-O-α-glucosylation of l-ascorbic acid from sucrose with high efficiency and perfect site-selectivity. Optimized synthesis with the enzyme from Bifidobacterium longum at 40 °C gave a concentrated product (155 g L−1; 460 mm), from which pure AA-2G was readily recovered in ∼50 % overall yield, thus providing the basis for advanced production. The peculiar pH dependence is suggested to arise from a “reverse-protonation” mechanism in which the catalytic base Glu232 on the glucosyl–enzyme intermediate must be protonated for attack on the anomeric carbon from the 2-hydroxyl of the ionized l-ascorbate substrate.
Original language | English |
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Pages (from-to) | 1387-1390 |
Number of pages | 4 |
Journal | ChemBioChem |
Volume | 18 |
Issue number | 14 |
DOIs | |
Publication status | Published - 18 Jul 2017 |
Keywords
- biocatalysis
- carbohydrates
- glycosylation
- phosphorylation
- reaction mechanisms
ASJC Scopus subject areas
- Biochemistry
- Molecular Medicine
- Molecular Biology
- Organic Chemistry
Cooperations
- NAWI Graz