FIGURE 5.

The T_m and ΔH_Tm of unfolding depend on the presence of cations and the CS. The midpoint of the unfolding transition (T_m) (panel A) and the enthalpy of unfolding at the midpoint of denaturation (ΔH_Tm) (panel B) were estimated from the thermal unfolding curves obtained in Fig. 4 (n = 3). Both the T_m and the ΔH_Tm of IαI unfolding are increased in the presence of Mg²⁺ or Mn²⁺. When the CS is removed (HC1·HC2 and IαI dissociated), the effect of Mg²⁺ is no longer observed. There still seems to be an effect of Mn²⁺. Mg²⁺ or Mn²⁺ thus seem to stabilize IαI and cause increased cooperatively in the unfolding. The effect depends on the presence of the CS. Significant values are indicated as: *, p < 0.05; **, p < 0.01; and ***, p < 0.001. The calculations are based on three technical replicates and error bars show the S.D.