Table 3.
Thermal denaturation parameters of RNase Sa and six mutants
| RNase | Td (°C) | ΔTda (°C) | ΔΔGb (kcal/mole) | ΔHcal (kcal/mole) | ΔHeff (kcal/mole) | Rc |
| pH 7.0 | ||||||
| Wild type | 49.0 | — | — | 92 | 103 | 0.89 |
| Gln38Ala | 52.5 | 3.5 | 1.0 | 109 | 110 | 0.99 |
| Glu41Lys | 46.5 | −2.5 | −0.7 | 90 | 100 | 0.90 |
| Glu54Gln | 43.1 | −5.9 | −1.7 | 81 | 87 | 0.93 |
| Arg65Ala | 45.6 | −3.4 | −1.0 | 81 | 90 | 0.90 |
| Glu74Lys | 52.1 | 3.1 | 0.9 | 101 | 113 | 0.89 |
| His85Gln | 49.1 | 0.1 | 0 | 90 | 89 | 1.01 |
| pH 5.5 | ||||||
| Wild type | 55.6 | — | — | 97 | 101 | 0.96 |
| Gln38Ala | 56.9 | 1.3 | 0.4 | 98 | 103 | 0.95 |
| Glu41Lys | 50.5 | −5.1 | −1.5 | 97 | 101 | 0.96 |
| Glu54Gln | 47.7 | −7.9 | −2.3 | 89 | 92 | 0.97 |
| Arg65Ala | 51.1 | −4.5 | −1.3 | 81 | 78 | 1.04 |
| Glu74Lys | 56.0 | 0.4 | 0.1 | 103 | 99 | 1.04 |
| His85Gln | 55.5 | −0.1 | 0 | 94 | 105 | 0.90 |
a ΔTd = Td (mutant) − Td (wild type).
b ΔΔG (= ΔTd × ΔSd) is the difference in the free energies of unfolding of wild-type and mutant RNase Sa at Td, and ΔSd (= ΔHcal/Td) is the entropy of unfolding of wild-type RNase Sa. A negative sign indicates a decrease in stability.
cR = ΔHcal/ΔHeff.