Formation of a stable L-ascorbic acid alpha-glucoside by mammalian alpha-glucosidase-catalyzed transglucosylation.
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 alpha-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 alpha-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 alpha-glucoside formed with alpha-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 alpha-glucosidase. These results indicate that it should be assigned the 2-O-alpha-glucoside structure. Consequently, it is concluded that mammalian alpha-glucosidase is able to form a very stable and nonreducing form of glucosylated AA through a specific transglucosylation reaction distinct from that of microbial alpha-glucosidase.
Yamamoto
I
I
Department of Immunochemistry, Faculty of Pharmaceutical Sciences, Okayama University, Japan.
Muto
N
N
Nagata
E
E
Nakamura
T
T
Suzuki
Y
Y
D000818:Animals; D001205:Ascorbic Acid / Q000031:analogs & derivatives* / Q000096:biosynthesis*; D001234:Aspergillus niger / Q000201:enzymology; D002851:Chromatography, High Pressure Liquid; D004795:Enzyme Stability; D005947:Glucose / Q000378:metabolism; D006168:Guinea Pigs; D006851:Hydrochloric Acid; D006868:Hydrolysis; D007421:Intestine, Small / Q000201:enzymology; D007668:Kidney / Q000201:enzymology; D008297:Male; D008320:Maltose / Q000378:metabolism; D009928:Organ Specificity; D010084:Oxidation-Reduction; D051381:Rats; D011919:Rats, Inbred Strains; D013056:Spectrophotometry, Ultraviolet; D000520:alpha-Glucosidases / Q000378:metabolism*
D008320:Maltose; D000520:alpha-Glucosidases; D005947:Glucose; D001205:Ascorbic Acid; D006851:Hydrochloric Acid