Table II.

Parameters Characterizing the Urea Unfolding of VHP and Hydrogen Bonding Variants in 50 mM Sodium Phosphate, pH 7.0, 25°C

Variant	Urea1/2a (M)	ΔUrea1/2b (M)	mc (cal mol−1M−1)	ΔG (H2O)d (kcal mol−1)	ΔΔGe (kcal mol−1)
WT	6.35	–	432	2.7	–
S43A	4.69	−1.66	448	2.1	−0.7
T54V	3.41	−2.94	452	1.5	−1.3

^aMidpoint of the unfolding curve. The error is ± 1%.

^bΔUrea_1/2 = Urea_1/2 (variant) − Urea_1/2 (WT).

^cThe slope of plots of ΔG versus [Urea]. The error is ± 10%.

^dΔG (H₂O) = the intercept of plots of ΔG versus [Urea] at 0M Urea.

^eFrom ΔUrea_1/2 × the average m value of WT and the variants (444 cal mol⁻¹M⁻¹). The negative values indicate a decrease in stability.