Figure 7. Temperature dependence of PaNhaP.
(A, B) At pH 6 transport activity increases by a factor of 2.1 for every 5°C rise in temperature, as measured by sodium efflux under symmetrical pH. The slight rise in fluorescence towards longer times at 40°C and above in A is due to increasing proton leakage of the proteoliposomes. (C, D) Effect of temperature on substrate affinity at 25°C (empty dots) and 30°C (filled squares) measured by ΔpH-driven sodium uptake in proteoliposomes using Acridine orange fluorescence. In contrast to vmax, Km does not change much with increasing temperature (1.56 ± 0.11 mM at 25°C; 1.85 ± 0.49 mM at 30°C).