Abstract
We have recently reported that the extracellular loop 12, the extracellular loop between transmembrane domain (TM) 12 and TM13, is a part of the sugar translocation pathway of Na+/glucose cotransporter type 1 (SGLT1) by making a chimera: the loop of Xenopus SGLT1-like protein (xSGLT1L) was substituted with the homologous region of rabbit SGLT1 (BBA 1758, 747-754, 2006). The chimera showed the increased apparent affinities for D-glucose (Glc) and myo-inositol (MI) compared to wild type xSGLT1L and transported both substrates equally. Next we made the second chimera in which the substituted region was expanded to both sides: the substituted region included about one-third of TM12 and almost of TM13. The second chimera transported Glc better than MI, this order was the reverse of the wild type xSGLT1L. From our results we will discuss about the important amino acids in the sugar translocation pathway of SGLT1. [J Physiol Sci. 2007;57 Suppl:S133]
