Table 1.

Anion dependence of the unfolding free energy of RNase A for urea unfolding at pH 3.0, 25°C

[Salt]	ΔGo	Cm	m
(M)	(kcal/mol)	(M)	(kcal/mol/M)
No salt added	3.28 ± 0.08	1.48 ± 0.06	2.24 ± 0.08
0.01 NaCl	3.26 ± 0.22	1.43 ± 0.08	2.29 ± 0.13
0.25 NaCl	3.69 ± 0.20	2.00 ± 0.02	1.85 ± 0.11
0.50 NaCl	4.48 ± 0.23	2.49 ± 0.02	1.80 ± 0.09
0.75 NaCl	5.07 ± 0.14	2.91 ± 0.05	1.75 ± 0.08
1.00 NaCl	5.28 ± 0.23	3.21 ± 0.06	1.64 ± 0.09
0.01 Na2SO4	4.20 ± 0.31	2.55 ± 0.10	1.67 ± 0.13
0.20 Na2SO4	6.38 ± 0.30	4.21 ± 0.08	1.52 ± 0.12
0.50 Na2SO4	7.91 ± 0.23	5.28 ± 0.09	1.50 ± 0.11
0.80 Na2SO4	8.56 ± 0.20	5.81 ± 0.08	1.47 ± 0.12
1.00 Na2SO4	10.07 ± 0.51	6.43 ± 0.05	1.57 ± 0.08
0.01 NaSCN	3.05 ± 0.34	1.44 ± 0.12	2.21 ± 0.16
0.05 NaSCN	2.91 ± 0.33	1.55 ± 0.11	1.87 ± 0.15
0.25 NaSCN	1.85 ± 0.25	1.50 ± 0.11	1.23 ± 0.15
0.50 NaSCN	1.43 ± 0.21	1.38 ± 0.12	1.03 ± 0.15
0.75 NaSCN	1.14 ± 0.28	1.04 ± 0.10	1.10 ± 0.10

ΔG_o is the unfolding free energy extrapolated to 0 M urea using the linear extrapolation formula ΔG = ΔG_o—mM; C_m is the urea molarity (M) at the midpoint of the transition curve where ΔG = 0 and ΔG_o = mC_m. See Materials and Methods for buffers.