TABLE 1.
Thermodynamic parameters from acid and base titrations
| Fluorescence
|
CD (275 nm)
|
CD (222 nm)
|
||||
|---|---|---|---|---|---|---|
| Val-66 | Asp-66 | Val-66 | Asp-66 | Val-66 | Asp-66 | |
| Acid titrations | ||||||
| pHmid* | 2.15 (0.01) | 2.90 (0.01) | 2.20 (0.04) | 2.94 (0.01) | 2.14 (0.02) | 2.91 (0.01) |
| ΔνH+* | 2.72 (0.14) | 4.09 (0.11) | 3.61 (0.92) | 2.15 (0.01) | 3.29 (0.28) | 3.99 (0.23) |
| pHmid† | 4.15 (0.10) | 4.28 (0.13) | 5.75 (0.60) | 5.35 (0.25) | ||
| ΔνH+† | 0.96 (0.14) | 0.67 (0.09) | 0.90 (0.70) | 0.55 (0.10) | ||
| Base titrations | ||||||
| pHmid* | 10.9 (0.10) | 11.10 (0.40) | 9.11 (0.15) | |||
| ΔνH+* | 0.66 (0.05) | 0.76 (0.43) | 1.09 (0.22) | |||
| pHmid† | 12.07 (0.02) | 10.40 (0.03) | 11.87 (0.01) | 10.34 (0.02) | 11.94 (0.03) | 10.38 (0.03) |
| ΔνH+† | 2.26 (0.27) | 4.6 (0.90) | 2.70 (0.20) | 4.34 (0.70) | 3.13 (0.53) | |
These parameters were obtained by nonlinear least-squares fit with Eqs. 1 and 2. The value pHmid refers to the midpoint of a transition. ΔνH+ refers to the cooperativity or to the number of H+ bound or released during the conformational transition.
*
Main, global unfolding.
†
Secondary, predenaturational transition.