The ion/substrate stoichiometry is 2 Na⁺ : 1 glucose for the Na⁺/glucose cotransporter 1 (SGLT1), whereas that for the Na⁺/glucose cotransporter 2 (SGLT2) is 1 Na⁺ : 1 glucose. Given this information, which isoform has a higher concentrative capacity (i.e., achieves a higher glucose concentration gradient by accumulating more glucose inside the cell relative to the concentration outside the cell).