Analyses of SGLT1 function and cooperative function of SGLT1 with disaccharidase

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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.