Table 2.
Time constants for dipolar interaction kinetics
| Helices | Mutant | Cβ-Cβ distance (Å) | Time constants (s) and fractional amplitudes |
||
|---|---|---|---|---|---|
| τ1 | τ2 | τ3 | |||
| B–F (c) | F42CR1/V167CR1 | 11.3 | <0.1 (0.89) | 3.5 ± 0.5 (0.09) | 27.2 ± 10.2 (0.02) |
| B–G (c) | F42CR1/I222CR1 | 11.5 | <0.1 (0.39) | 2.9 ± 0.6 (0.38) | 123 ± 23.7 (0.23) |
| B–G (e) | G63CR1/L201CR1 | 13.1 | <0.1 | Not resolved | Not resolved |
| C–F (c) | A103CR1/M163CR1 | 10.8 | <0.1 (0.70) | 3.3 ± 0.3 (0.21) | 84.3 ± 15.6 (0.09) |
| D–G (e) | A126CR1/L201CR1 | 15.9 | <0.1 (0.46) | 5 ± 0.4 (0.42) | 69 ± 14.8 (0.12) |
| F–G (c) | V167CR1/I222CR1 | 13.2 | <0.1 | Not resolved | Not resolved |
Summary of time constants obtained from least-square fitting of the kinetics of dipolar interactions between spin labels on various helix pairs in BR. Cytoplasmic and extracellular label pairs are indicated by c and e, respectively. The Cβ-Cβ distances were obtained from the crystallographic structure, PDB code 1c3w (16). The fractional amplitudes with the time constant are shown in parentheses. The time constants and their standard errors are from three to five replicate experiments. Kinetics and fits are shown in Fig. 5.