Figure 3. Apparent unidirectionality of Lyp1-mediated lysine transport in proteoliposomes.

(a): Schematic showing the generation of a membrane potential (ΔΨ, red) by a valinomycin-mediated potassium diffusion potential and pH gradient (ΔpH, green) formation by an acetate diffusion potential. Together the ΔΨ and ΔpH form the proton motive force (PMF = ΔΨ−ZΔpH, where Z equals 2.3RT/F and R and F are the gas and Faraday constant, respectively, and T is the absolute temperature). (b) Transport of lysine by Lyp1-GFP-containing proteoliposome. (c) Transport of lysine by LysP-containing proteoliposomes. The effect of 10 μM FCCP (circles) and 20 mM lysine (1000x fold excess of unlabeled lysine, triangles) on the transport of 20 μM ¹⁴C-lysine by Lyp1 and LysP is shown; time-point of addition is indicated by arrows, and the levels of accumulation at this point are 15-fold for Lyp1 and 25-fold for LysP. All fits and errors are derived from three independent experiments.