Fig. 2.

Competitive binding of Na⁺ and H⁺ to the I. tartaricus c-ring. The Insets show representative NaCl titrations of the I. tartaricus c-ring at similar protein concentrations and three different pH values (the error in the pH represents the different values measured in the dialysis buffer before ITC experiment and in the protein solution after titration). The heat signals released per injection normalized with respect to all relevant concentrations (black circles) can be fitted by a Wiseman isotherm (Eq. 1) (black curve) (43, 44), from which the apparent dissociation constant, K_d^app, and apparent enthalpy, ΔH_o, can be derived.