Formation of a stable L-ascorbic acid a-glucoside by mammalian a-glucosidase-catalyzed transglucosylation
Formation of a stable L-ascorbic acid a-glucoside by mammalian a-glucosidase-catalyzed transglucosylation
- Biochimica et Biophysica Acta, 1035(1), p.44-50, 1990 .
Enzymatic transglucosylation from maltose to L-ascorbic acid (AA)with mammalian tissue homogenates was determined by a high-performance liquid chromatography method and compared with the reaction catalyzed by a-glucosidase from Aspergillus niger. The homogenates of small intestine and kidney had a high transglucosylase activity to form a new type of glucosylated AA, which was associated with a-glucosidase activity. The new compound was demonstrated to be an equimolar conjugate of AA and glucose by the spectral and quantitative analyses. In particular, it showed a high stability in a neutral solution and no reducing activity toward cytochrome c and a dye. These properties were very different from those of AA and L-ascorbic acid a-glucoside formed with a-glucosidase from A. niger, but they were consistent with those of L-ascorbic acid 2-O-phosphate and L-ascorbic acid 2-O-sulfate. Moreover, it exhibited a reducing power associated with AA after mild acid hydrolysis or treatment with rat intestinal a-glucosidase. These results indicate that it should be assigned the 2-O-a-glucoside structure. Consequently, it is concluded that mammalian a-glucosidase is able to form a very stable and nonreducing form of glucosylated AA through a specific transglucosylation reaction distinct from that of microbial a-glucosidase.
Enzymatic transglucosylation from maltose to L-ascorbic acid (AA)with mammalian tissue homogenates was determined by a high-performance liquid chromatography method and compared with the reaction catalyzed by a-glucosidase from Aspergillus niger. The homogenates of small intestine and kidney had a high transglucosylase activity to form a new type of glucosylated AA, which was associated with a-glucosidase activity. The new compound was demonstrated to be an equimolar conjugate of AA and glucose by the spectral and quantitative analyses. In particular, it showed a high stability in a neutral solution and no reducing activity toward cytochrome c and a dye. These properties were very different from those of AA and L-ascorbic acid a-glucoside formed with a-glucosidase from A. niger, but they were consistent with those of L-ascorbic acid 2-O-phosphate and L-ascorbic acid 2-O-sulfate. Moreover, it exhibited a reducing power associated with AA after mild acid hydrolysis or treatment with rat intestinal a-glucosidase. These results indicate that it should be assigned the 2-O-a-glucoside structure. Consequently, it is concluded that mammalian a-glucosidase is able to form a very stable and nonreducing form of glucosylated AA through a specific transglucosylation reaction distinct from that of microbial a-glucosidase.