FIGURE 2.

A kinetic model of Na and glucose transport by SGLT1

The SGLT1 protein in the plasma membrane is represented as a double-gated structure. External Na binds first to the Na2 and Na1 sites to open the external gate and allow glucose to bind in a central pocket. This outer barrier closes to occlude the sugar from the external aqueous solution. Upon opening of the internal barrier, Na and glucose pass through an aqueous vestibule to reach the cytoplasm. The cycle is completed by the return of the protein to the starting position. The rate of transport is governed by the opening and closing of the outer and inner barriers.