Table 1.
Binding and Electron Transfer Parameters for single and double mutant reactions of RCs modified at Tyr-M295 and cyt c2 modified at Arg-C32 (pH = 7.5)a
| RC Strain | cyt c2 | ke(× 106s−1) | k2 (× 108M−1s−1) | KD(μM) | ΔΔG (meV) |
|---|---|---|---|---|---|
| Native | Native | 1.0 | 13.1 | 0.30 | 0 |
| Tyr-M295 →Phe | Native | 1.1 | 13.4 | 0.38 | 6 |
| Tyr-M295 →Trp | Native | 0.9 | 12.5 | 0.44 | 10 |
| Tyr-M295 →Asn | Native | 1.0 | 13.2 | 0.78 | 24 |
| Tyr-M295 →Leu | Native | 0.9 | 13.1 | 0.89 | 28 |
| Tyr-M295 →Ala | Native | 1.0 | 12.1 | 0.91 | 28 |
| Native | Arg-C32→Lys | 0.9 | 4.6 | 1.7 | 44 |
| Native | Arg-C32→Gln | 0.6 | 7.8 | 15 | 100 |
| Native | Arg-C32→Ala | 0.8 | 6.1 | 24 | 112 |
| Tyr-M295 →Leu | Arg-C32→Lys | 0.9 | 3.4 | 1.8 | 46 |
| Tyr-M295 →Leu | Arg-C32→Gln | 0.6 | 13.1 | 17 | 103 |
| Tyr-M295 →Ala | Arg-C32→Ala | 0.7 | 6.7 | 31 | 118 |
a
ke is the rate constant for the fast, first order electron transfer. kon is the second order rate constant. KD is the dissociation constant for the cyt c2:RC complex. ΔΔG = RTln(KD,i/KD,0) is the difference in binding free energy between the mutant and native RCs. The experimental precision for the measured values of the rates and KD is ± 15%. The uncertainty in the free energies is ± 5meV