TABLE 1.
The experimental apparent pKa values of histidines in SNase as a function of KCl and KSCN concentration
| Salt concentration | His-46* | His-121* | Model calculation His-46 |
|---|---|---|---|
| 0.02 M KCl | 5.71 ± 0.02 | 4.91 ± 0.03 | 5.70 |
| 0.10 M KCl | 5.86 ± 0.04 | 5.30 ± 0.06 | 5.83 |
| 0.50 M KCl | 5.95 ± 0.02 | 5.56 ± 0.02 | 5.99 |
| 1.50 M KCl | 6.10 ± 0.04 | 5.85 ± 0.03 | 6.08 |
| 0.10 M KSCN | 6.01 ± 0.04 | 5.53 ± 0.04 | 5.98 |
| 0.50 M KSCN | 6.30 ± 0.03 | 6.12 ± 0.03 | 6.24 |
*
Values from Lee et al. (2002).
We have also added the result of model calculations described in the text. For the theoretical calculations the salt labeled KCl (KSCN) represents B− = 0 × 10−50 J m3 (B− = −10 × 10−50 J m3). In the theoretical calculations the actual (salt independent) pKa = 6.25 of histidine was chosen to get agreement with the experimental result for His-46 in 0.02 M KCl.