Table 1.
Electrochemical parameters measured by CD spectrum, protein film volatammetry, and kinetic titration
| Strains | Em values from CD spectra (mV) | Protein Film Voltammetry | Kinetic titration at 83% reduced quinine pool 4) | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Eacid (mV) | Ebase (mV) | pKox1 | pKox2 | pKred1,2 | pKA | pKB | Vopt | ||
| wild-type/BH6 1) | 303 ± 4 2) / 312 ± 5 3) | 308 ± 3 | −134 ± 6 | 7.6 ± 0.1 | 9.6 ± 0.1 | 12.4 ± 0.4 | 6.66 ± 0.10 | 9.14 ± 0.26 | 973.3 |
| S154T | 260 ± 5 2) | 288 ± 3 | −151 ± 7 | 7.71 ± 0.14 | 9.32 ± 0.15 | 12.2 ± 0.1 | 6.83 ± 0.12 | 8.48 ± 0.14 | 826.1 |
| S154C | 313 ± 5 2) | 324 ± 4 | −97 ± 6 | 7.17 ± 0.11 | 9.77 ± 0.13 | 12.0 ± 0.1 | 6.29 ± 0.05 | 8.46 ± 0.06 | 804.0 |
| S154A | 167 ± 6 2) | 178 ± 4 | −239 ± 10 | 8.06 ± 0.15 | 9.89 ± 0.17 | 12.5 ± 0.1 | 7.52 ± 0.20 | 10.2 ± 0.28 | 199.2 |
| Y156F | 256 ± 4 3) | 252 ± 4 | −165 ± 6 | 7.76 ± 0.15 | 8.83 ± 0.21 | 11.8 ± 0.1 | 6.90 ± 0.06 | 8.54 ± 0.08 | 714.6 |
| Y156W | 198 ± 3 3) | 208 ± 3 | −228 ± 4 | 7.87 ± 0.09 | 9.25 ± 0.11 | 12.2 ± 0.1 | 6.97 ± 0.08 | 9.69 ± 0.12 | 242.7 |
1)
The wild-type strain in this work is a complementary mutant strain of Rb. sphaeroides BC17, which contains the pRK415 with a modified fbc operon which has a histidine-tag at the C-terminus of the cyt b gene. The protein film voltammetric data of the wild-type was reported [44].
2)
The values are measured at pH 7.4.
3)
The data represent the limiting value for Em at pH << pK1, as described in [59].
4)
Vopt is the optimal reaction rate achieved when the first protonable group is deprotonated (pKA) and the second group is protonated (pKB), according to the following equation from the reference [148].