Figure 4. Binding heat capacity changes.

Binding isotherms and enthalpies derived from ITC for (a) Glt_Ph^out and (b) Glt_Phⁱⁿ. Left panels, thermal powers and heats measured at 15 (solid circles and upper insets, respectively) and 35 °C (solid triangles and lower insets, respectively) are shown. The solid lines are the best fits to independent binding sites model. The fitted ΔH in kcal/mol, K_D values in nM and n values were, respectively, in (a): −13.5, 154, 1.0 at 15 °C and −19.4, 1278 and 1.1 at 35 °C; and (b): −12.3, 373, 0.7 at 15 °C and −25.2, 540 and 0.8 at 35 °C. Right panels, temperature dependencies of the binding enthalpies for Asp in the presence of: 10 mM Na⁺ (solid circles), 1 M Na⁺ (open circles), and 30 mM Na⁺, 0.6 mM TBA (solid squares). The data were fitted to straight lines with the slopes corresponding to the ΔCps of binding: −297, −131, −171 cal mol⁻¹ K⁻¹, respectively, for Glt_Ph^out and −608, −184, −198 cal mol⁻¹ K⁻¹, respectively, for Glt_Phⁱⁿ.