The transport of extracellular glucose (Glc) and galactose (Gal) into the cytosol, coupled to the uptake of two sodium ions for each hexose transported, is mediated by sodium/glucose cotransporter 1 (SLC5A1, also known as SGLT1), localized on the luminal surfaces of enterocytes (Wright et al. 2004). The specificity of SLC5A1 has been worked out by studying sugar transport in plasma membrane vesicles containing recombinant human SLC5A1 protein (Quick et al. 2003). Consistent with these in vitro results, children lacking functional SLC5A1 protein fail to absorb dietary glucose and galactose (Martin et al. 1996). The transport activity of SLC5A1 was decreased upon co-expression of regulatory solute carrier protein family 1 member 1 (RSC1A1, aka RS1). RSC1A1 exhibits glucose-dependent, short-term inhibition of SLC5A1 by inhibiting the release of vesicles from the trans-Golgi network (Veyhl et al. 2006).