Valence associated with transitions of several forms of the ASCT2 transport domain. (A) Setup used for the APBS calculations. Blue color indicates inside positive or negative membrane potential (+ or −100 mV), and red color indicates 0-mV membrane potential. (B) Illustration of the conformational change of an individual transport domain from outward- to inward-facing. (C) Relative change in the total electrostatic energy for the outward-facing to inward-facing transition of an individual subunit for the apo transporter (red), and the forms with 2 Na⁺ bound (black) and 2 Na⁺ and alanine bound (ΔE was set to 0 k_bT at 0 mV). (D) Valences calculated from the slopes of C.