Table III.

Parameters Characterizing the Thermal Unfolding of VHP and Hydrogen Bonding Variants in 50 mM Sodium Phosphate, pH 7.0

Variant	ΔHma (kcal mol−1)	ΔSmb (cal mol−1 K−1)	Tmc (°C)	ΔTmd (°C)	Δ(ΔG)e (kcal mol−1)	Δ(ΔG)f (kcal mol−1)
WT	31	89	74.4	–	–	–
S43A	28	86	65.0	−9.4	−0.8	−0.6
T54V	26	78	61.6	−12.8	−1.1	−1.1

^aEnthalpy of unfolding at T_m. The error is ± 2 kcal mol⁻¹.

^bΔH_m/T_m. The error is ± 5 cal mol⁻¹ K⁻¹.

^cMidpoint of the unfolding curve. The error is ± 0.5°C.

^dΔT_m = T_m (variant) − T_m (WT).

^eΔ(ΔG) = ΔT_m × the average ΔS_m value of WT and the variants (84 cal mol⁻¹ K⁻¹).

^fCalculated using the Gibbs-Helmholtz equation at a reference temperature = 67.0°C. The value for ΔC_p was 0.374 kcal mol⁻¹ K⁻¹ (see text), and the value for ΔH_m was 23 kcal mol⁻¹ at 67.0°C. The negative values indicate a decrease in stability.