Table 5.

Parameters characterizing the thermal unfolding of RNase Sa and the 3K and 5K variants between pH 2 and 10

Sa variant	pH	Tma (°C)	ΔHmb (kcal mole−1)	ΔSmc (cal K−1 mole−1)	ΔG (25°C)d (kcal mole−1)
Wild type	2	27.3	56	186	0.42
	3.3	42	85	270	3.88
	5	54.2	108	330	7.59
	7	47.2	91	284	5.11
	8.3	39.5	92	294	3.75
	9	35.4	78	253	2.36
	10	30.1	72	237	1.15
3K	2	27.9	60	199	0.56
	3.3	44.4	83	261	4.15
	4	50.8	89	275	5.48
	5	49.4	91	282	5.44
	6	50.0	84	260	4.99
	7	40.7	77	245	3.24
	8.3	31.9	70	230	1.46
	9	29.1	62	205	0.80
	10	22.3	50	169	−0.48
5K	2	25.6	62	208	0.12
	3	41.4	77	245	3.31
	4	52.4	85	261	5.35
	5	53.3	87	267	5.62
	6	51.3	85	262	5.22
	7	47.3	82	256	4.50
	8	44.2	76	240	3.70
	9	42.7	72	228	3.50
	10	36.4	59	191	1.85

^a Midpoint of the thermal unfolding curve. The standard deviation is ±0.3°C.^b Enthalpy change at T_m. The standard deviation is ±5%.^c ΔS_m = ΔH_m/T_m.^d Calculated with Equation 1 using the T_m and ΔH_m values in this table and a value of 1.52 kcal K⁻¹ mole⁻¹ for ΔCp (Pace et al. 1998).