Figure 5. Influence of the Membrane Potential on PamNTT1 and Mitochondrial AAC-Mediated Uptake.
Reconstituted recombinant PamNTT1 or reconstituted mitochondrial total membrane proteins were incubated with 50 μM [α32P]-labelled ADP or ATP. Concentration of internal ATP (A) or ADP (B) was 10 mM. For transport measurements in absence of a membrane potential (0) similar buffer media were present at the proteoliposomal exterior and interior. Generation of a membrane potential was achieved by addition of 20 μM of valinomycin to proteoliposomes with different potassium concentrations at the interior and exterior. According to the flux of the applied potassium concentrations, the corresponding membrane potential was calculated. Potassium influx resulted in a theoretical external negative membrane potential (−) of −40 mM, and potassium efflux in a theoretical external positive membrane potential (+) of +40 mV. The exchange rate is given in % normalized to the transport in absence of a membrane potential (100%). Data of AAC-mediated (gray bars) and NTT-mediated (white bars) nucleotide exchange are the means of three independent experiments.