Enzymatic formation of a nonreducing L-ascorbic acid α-glucoside: Purification and properties of α-glucosidases catalyzing site-specific transglucosylation from rat small intestine
Enzymatic formation of a nonreducing L-ascorbic acid α-glucoside: Purification and properties of α-glucosidases catalyzing site-specific transglucosylation from rat small intestine
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DOI：
10.1093/oxfordjournals.jbchem.a123030
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发表时间：
1990-02
影响因子：
2.7
通讯作者：
N. Muto;Tomoe Y. Nakamura;I. Yamamoto
中科院分区：
文献类型：
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作者：
N. Muto;Tomoe Y. Nakamura;I. Yamamoto
我们以前已经发现，一些哺乳动物组织匀浆可以催化从麦芽糖到L-抗坏血酸（AA）的独特转葡糖基化，产生化学稳定的AA衍生物，L-抗坏血酸α-葡萄糖苷（AAG）。在本研究中，负责这种转葡萄糖基化的酶是从大鼠肠膜中分离出来的。AAG的形成通过使用ODS柱的HPLC测定。在纯化过程中，AAG形成酶的比活性与α-葡糖苷酶（麦芽糖水解酶）的比活性平行增加，并且两种中性α-葡糖苷酶（称为α-葡糖苷酶I和II）被纯化至表观均一性。其酶学性质分别与麦芽糖酶[EC 3.2.1.20]和蔗糖酶-异麦芽糖酶复合物[EC 3.2.1.48/10]相对应。这两种酶都可以通过在所检测的二糖中仅裂解麦芽糖来形成AAG，尽管α-葡糖苷酶I具有比其他酶高得多的活性。AAG的形成和麦芽糖的水解都依赖于培养温度，在60 ℃时具有最大活性，但它们的最适pH值之间存在明显差异。由此形成的AAG也可以被纯化的酶水解。从这些结果，它的结论是，膜结合中性α-葡萄糖苷酶从大鼠肠道具有位点特异性转葡萄糖基酶活性，形成非还原性AAG，这是不同于L-抗坏血酸-6-O-α-D-葡萄糖苷。
We have previously found that some mammalian tissue homogenates can catalyze a unique transglucosylation from maltose to L-ascorbic acid (AA), resulting in a chemically stable AA derivative, L-ascorbic acid alpha-glucoside (AAG). In the present study, the enzyme responsible for this transglucosylation was isolated from rat intestinal membrane. The formation of AAG was determined by HPLC with an ODS column. The specific activity of AAG-forming enzyme was increased in parallel with that of alpha-glucosidase (maltose hydrolase) during the purification, and two neutral alpha-glucosidases, termed alpha-glucosidases I and II, were purified to apparent homogeneity. Their enzymological properties showed that they corresponded to maltase [EC 3.2.1.20] and sucrase-isomaltase complex [EC 3.2.1.48/10], respectively. Both enzymes could form AAG by splitting only maltose among the disaccharides examined, although alpha-glucosidase I possessed a considerably higher activity than the other enzyme. Both AAG formation and maltose hydrolysis were dependent on incubation temperature with the maximal activity at 60 degrees C, but there was an apparent difference between their pH optima. AAG thus formed could also be hydrolyzed by the purified enzymes. From these results, it is concluded that membrane-bound neutral alpha-glucosidases from rat intestine have site-specific transglucosylase activity to form nonreducing AAG which is distinct from L-ascorbic acid-6-O-alpha-D-glucoside.