Analyses of SGLT1 function and cooperative function of SGLT1 with disaccharidase

对SGLT1介导的葡萄糖结合物转运进行了功能分析。从结合(识别)和转位(转运)两个方面评价苷元对SGLT1功能的影响。除水杨素外，所有研究的葡萄糖结合物都被归类为T类(可转运化合物)。SGLT1转运的周转率不依赖于分子大小。此外，虽然苯基β-葡萄糖对取代基的转化率顺序为NH_2&GT；OH&GT；NO_2，但结合亲和力(Km)是相似的。这表明SGLT1的结合和转位受到取代基的影响，但影响程度不同。分子模拟分析表明，糖苷的葡萄糖构象为4^C_1椅型，这与已有的结果(对硝基-1-β-葡萄糖苷和对乙酰氨基酚β-葡萄糖苷)相同。因此，SGLT1的备用空间位置影响SGLT1的功能。在Caco-2细胞中发现了双糖偶联酶、麦芽糖酶和LPH(乳糖酶/根茎苷水解酶)的双糖酶活性。此外，在经三碘甲腺原氨酸处理的Caco-2细胞中检测到SGLT1活性，而在未处理的Caco-2细胞中未检测到明显的SGLT1活性。提示Caco-2细胞可用于双糖酶和SGLT1的研究。

Functionai analysis of SGLT1-mediated transport of glucose conjugates was performed. Influence of aglycone moiety on SGLT1 function was evaluated in terms of binding (recognition) and translocation (transport). All of glucose conjugates studied in this project, except salicin, were classified to Class T (transportable compound). Turnover of SGLT1for transport did not depend on molecular size. Furthrmore, although the order of turnover rate of p-substituents of phenyl β-glucose was NH_2 > OH > NO_2, binding affinity (Km) were similar to each other. This indicated that the binding and translocation of SGLT1 were affected by substituents, but the influcences were different. Molecular modeling analysis showed that glucose conformation of glucosides were in 4^C_1 chair form, which is the same as previous results (p-nitrophyeny1 β-glucoside and acetaminophen β-glucoside). Therefore, the position of spare apace of SGLT1 affects SGLT1 function.Disaccharidase activities of disaccharide conjugate, maltase and LPH(lactase/phloridzin hydrolase) were found in Caco-2 cells. Furthermore, SGLT1 activity was detected in tri-iodothyronine-treated Caco-2 cells, although significant activity of SGLT1 was not detected i non-treated Caco-2 cells. This suggest that Caco-2 cells may be useful for the study of disaccharidase and SGLT1.