Table VIII.
The Stability of nSS Trx and Its Intrahelical Disulfide Mutants Under Oxidized and Reduced Conditions as Measured by Isothermal Denaturation Studies at 25°C, pH 7.0, and DSC Studies
| Protein | ΔG° (25°C)a (kcal mol−1) | C m (M)b | ΔΔG° (25°C)c (kcal mol−1) | ΔC m (M) | T m (°C)d | ΔT m (°C) | ΔH°(T m) (kcal mol−1)e |
|---|---|---|---|---|---|---|---|
| nSS Trx | 5.5 ± 0.3 | 1.6 | — | — | 77.4 | — | 117.0 |
| CIDC (59–62) | 4.1 ± 0.1 | 1.2 | −1.4 | −0.4 | 62.0 | −15.4 | 52.9 |
| CIPC (59–62) | 3.5 ± 0.1 | 1.0 | −2.0 | −0.6 | 65.6 | −11.8 | 67.1 |
| CGPC (59–62)f | — | — | — | — | — | — | — |
| CKGC (95–98) | 3.8 ± 0.1 | 1.1 | −1.5 | −0.4 | 66.1 | −11.3 | 67.4 |
| CGPC (95–98) | 4.3 ± 0.1 | 1.2 | −1.2 | −0.4 | 66.2 | −11.2 | 62.0 |
| CDQC (60–63)g | 1.7 ± 0.1 | 0.5 | −3.8 | −1.1 | — | — | — |
| CGQC (96–99)h | — | — | — | — | — | — | — |
| CIDC (59–62)redi | 4.6 ± 0.1 | 1.3 | −0.9 | −0.3 | — | — | — |
| CIPC (59–62)redi | 3.3 ± 0.4 | 1.0 | −2.2 | −0.6 | — | — | — |
| CKGC (95–98)redi | 4.3 ± 0.9 | 1.2 | −1.2 | −0.4 | — | — | — |
| CGPC (95–98)redi | 3.4 ± 0.1 | 1.0 | −2.1 | −0.6 | — | — | — |
| CDQC (60–63)redi | 3.8 ± 0.1 | 1.1 | −1.7 | −0.5 | — | — | — |
| CGQC (96–99)redi | 2.9 ± 0.1 | 0.8 | −2.6 | −0.8 | — | — | — |
a
All isothermal melts were fitted with the same m value of –3.4 kcal mol−1.
b,d,eApproximate errors are 0.05M for C m, 1°C for T m, and 5% for ΔH°(T m).
c
ΔΔG° = ΔG°(mutant)−ΔG°(nSS Trx) where ΔG° is free energy of unfolding.
f
Protein CGPC (59–62) was unstable and could not be purified.
g
CDQC (60–63) could not be characterized by DSC since it precipitated during thermal melt.
h
CGQC (96–99) underwent drastic structural change on formation of disulfide bond.
i
All melts in the reduced state were carried out in the presence of 20‐fold molar excess of protein.