Yamamoto I, Muto N, Nagata E, Nakamura T, Suzuki Y
Department of Immunochemistry, Faculty of Pharmaceutical Sciences, Okayama University, Japan.
Biochim Biophys Acta. 1990 Jul 20;1035(1):44-50. doi: 10.1016/0304-4165(90)90171-r.
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.
采用高效液相色谱法测定了麦芽糖与L-抗坏血酸（AA）在哺乳动物组织匀浆中的酶促转葡糖基化反应，并与黑曲霉α-葡糖苷酶催化的反应进行了比较。小肠和肾脏匀浆具有较高的转葡糖基酶活性，可形成一种新型的糖基化AA，这与α-葡糖苷酶活性有关。通过光谱和定量分析表明，新化合物是AA与葡萄糖的等摩尔共轭物。特别是，它在中性溶液中表现出高稳定性，对细胞色素c和一种染料没有还原活性。这些性质与用黑曲霉α-葡糖苷酶形成的AA和L-抗坏血酸α-葡糖苷的性质非常不同，但与L-抗坏血酸2-O-磷酸酯和L-抗坏血酸2-O-硫酸酯的性质一致。此外，在温和酸水解或用大鼠肠道α-葡糖苷酶处理后，它表现出与AA相关的还原能力。这些结果表明它应具有2-O-α-葡糖苷结构。因此，可以得出结论，哺乳动物α-葡糖苷酶能够通过一种不同于微生物α-葡糖苷酶的特异性转葡糖基化反应，形成一种非常稳定且无还原活性的糖基化AA形式。
