Table 1.
Summary of ion-TBA kinetic parameters in 50 mM Tris buffer, observed by the conformational change they induce. Rates of ion binding were obtained by global mono-exponential fits. The ion dissociation rate kOFF represents the minimum rate to allow the observed unfolding rate kU. The folding rate kF was the observed rate at highest salt concentration tested. Values shown represent the mean (±standard deviation, SD) of three independent experiments.
| Ion | kON (M−1s−1) | kOFF = kU (10−1 s−1) | KD (mM) | kF (s−1) | KF (No Unit) |
|---|---|---|---|---|---|
| NH4+ | 2.96 ± 0.8 | 3.07 ± 0.3 | 104 ± 40 | 1.18 ± 0.23 | 3.84 ± 0.8 |
| K+ | 15.2 ± 1.7 | 1.20 ± 0.01 | 7.89 ± 1.3 | 1.26 ± 0.14 | 10.4 ± 1.1 |
| Na+ | - | - | - | - | - |
| Li+ | - | - | - | - | - |
kON = rate constant of ion binding to TBA (M−1s−1); kOFF = minimum rate constant of ion dissociation from TBA (s−1); KD = equilibrium dissociation constant of ion (M) calculated by KD = kOFF/kON; kF = observed rate of TBA folding (s−1); kU = rate constant of TBA unfolding (s−1); KF = ratio of TBA folding versus unfolding calculated by KF = kF/kU.