Table 1. Structural-derived energetic parameters calculated based on the crystal structures of N-terminal truncated forms of RIα.

Parameter	cAMP-boundPDB 1RGS(residues 113–376)	cAMP-free (apo)*PDB 1RL3(residues 109–376)	cAMP-free (apo)** PDB 2QCS(residues 90–380)
ΔASA ap (Å2)	18746	19535	19938
ΔASA pol (Å2)	10598	11526	12194
ΔC p_calc (kcal/K·mol)	5.7	5.8	5.8
ΔH calc_60 (kcal/mol)	174.5	197.0	214.6
T m (°C)	71	62.5	62.5
ΔH calc_at Tm (kcal/mol)	236	212	230

Experimental values for cAMP-free (apo)-RIα(92–381); T _m = 62.5±0.1°C, ΔH = 111.6±2.9 kcal/mol and ΔH ^VH = 96.3±2.1 kcal/mol.

Experimental values for cAMP-bound RIα(92–381); T _m = 71.0±0.1°C, ΔH = 120.4±1.2 kcal/mol and ΔH ^VH = 139.9±1.4 kcal/mol (with 800 µM cAMP; 4 µM RIα(92–381)).

*The cGMP present in site A was not included the calculations.

**The C structure was not included in the calculations.

Theoretical values for the unfolding heat capacity (ΔC _{p_calc}) and enthalpy changes at 60°C (ΔH _{calc_60}) and at the T_m (ΔH _{calc_at Tm}) were calculated from the changes in apolar and polar accessible surface area (ΔASA _ap and ΔASA _pol) upon unfolding using structure-energetics correlations (see [22] for equations).