Figure 6. Proton-coupled uptake of [14C]lactate by liposomes in the presence of an inwardly directed proton gradient (pHout=6.0, pHin=7.0), in the absence of a proton gradient (pHin=pHout=7.0), or after dissipation of the proton gradient by the addition of the protonophorous uncoupler DNP.
The liposomes were prepared from egg-yolk phosphatidylcholine, and the uptake of lactate was determined as described in [120]. The amount of radiolabelled lactate taken up by the proteoliposomes was measured at the indicated time points. An inwardly directed pH gradient was established across the liposomal membranes by the addition of HCl as required to lower the pH of the reaction medium to 6.0 at the start of the assay.