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Figure S3. Effect of high valinomycin concentration on ΔpH and Δ ψ. Under our conditions, even high concentrations of valinomycin could not completely collapse the Δψ (see Fig. 5 D and this figure). This could be a consequence of a Donnan equilibrium contributing to the overall Δψ. The K+ concentration in the IMV lumen was low (∼1 mM). In contrast, the external K+ concentration in our transport assays was 50 mM. This K+ concentration difference can support a Donnan potential of ∼100 mV (positive inside). (A) The presence of a ΔpH determined as in Fig. 5 in the presence and absence of 50 µM valinomycin, as indicated. (B) The presence of a Δψ determined as in Fig. 5 in the presence and absence of 50 µM valinomycin, as indicated.