Table III.
Parameters Characterizing the Urea and GuHCl Unfolding of RNase Sa and the Stabilized Variants in 30 mM MOPS, pH 7.0, 25°C
| Variant | Denaturant | D1/2a (M) | ΔD1/2b (M) | mc (kcal/mol/M) | ΔG° (H2O)d (kcal/mol) | ΔΔG°e (kcal/mol) |
|---|---|---|---|---|---|---|
| WT | GuHCl | 2.99 | — | 2.43 | 7.3 | — |
| 2S | GuHCl | 2.70 | –0.29 | 2.61 | 7.1 | –0.7 |
| 7S | GuHCl | 4.44 | 1.45 | 2.52 | 11.2 | 3.7 |
| 8S | GuHCl | 5.40 | 2.41 | 2.51 | 13.6 | 6.1 |
| WT | Urea | 6.06 | — | 0.96 | 5.8 | — |
| 2S | Urea | 6.51 | 0.45 | 1.02 | 6.6 | 0.4 |
a
Midpoint of the unfolding curve. The error is ±1%.
b
ΔD1/2 = D1/2 (variant) – D1/2 (WT).
c
The slope of plots of ΔG versus [denaturant]. The error is ±10%.
d
ΔG° (H2O) = the intercept of plots of ΔG versus [denaturant] at 0 M denaturant.
e
From ΔD1/2 × the average m value of WT and the variants. Positive values indicate increases in stability.