Figure 8. Effect of substrates on hPEPT1 charge distribution.

A, reduction in Q_max by Gly-Sar and selected drugs in representative oocytes expressing WT (black bar), S117N (grey bar) and G419A (white bar) hPEPT1. B, shift of V_0.5 in the same oocytes. Data are from the same oocytes shown in Figs 6 and 7. The apparent maximum charge (Q_max) and the voltage for 50% charge movement (V_0.5) in a Na⁺ buffer at pH 5.0 were determined from the Q–V relations and the Boltzmann equation (see Methods).