Substrate specificity of a chimera made from Xenopus SGLT1-like protein and rabbit SGLT1

摘要

To characterize the sugar translocation pathway of Na+/glucose cotransporter type I (SGLT I), a chimera was made by substituting the extracellular loop between transmembrane domain (TM) 12 and TM13 of Xenopus SGILT1-like protein (xSGLT1L) with the homologous region of rabbit SGLT I. The chimera was expressed in Xenopus oocytes and its transport activity was measured by the two-microelectrode voltage-clamp method. The substrate specificity of the chimera was different from those of xSGLT1L and SGLT1. In addition the chimera's apparent Michaelis-Menten constant (K-m) for myo-inositol, 0.06 mM, was about one fourth of that of xSGLT1L, 0.25 mM, while the chimera's apparent K-m for D-glucose, 0.8 mM, was about one eighth of that of xSGLT1L, 6.3 mM. Our results suggest that the extracellular loop between TM12 and TM13 participates in the sugar transport of SGLT1. (c) 2006 Elsevier B.V All rights reserved.