Table 1.
Kinetic analysis of AChRs with mutations in the α -subunit
| AChR | k+1 | k−1 | K1 (μm) | k+2 | k−2 | K2 (μm) | β1 | α1 | θ1 | β2 | α2 | θ2 | k+b | k−b | KB (mm) | ΔG° (kcal/mol) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Wild type | 271 ± 16 | 7190 ± 545 | 26 | 192 ± 6 | 19,300 ± 309 | 101 | 67 ± 8 | 2190 ± 160 | 0.03 ± 0.0043 | 43,700 ± 999 | 1650 ± 32 | 26.5 ± 0.79 | 26 ± 1 | 113,000 ± 1690 | 4.3 | |
| Mutant | ||||||||||||||||
| αF135L | 146 ± 33 | 3760 ± 992 | 26 | 254 ± 19 | 26,600 ± 1540 | 105 | NA | NA | 5980 ± 100 | 6230 ± 55 | 0.96 ± 0.018 | 20 ± 2 | 97,700 ± 3560 | 4.9 | 1.94 ± 0.04 | |
| αF137L | 185 ± 12 | 1780 ± 166 | 9.6 | 225 ± 7.7 | 11,100 ± 271 | 49 | NA | NA | 85,600 ± 2010 | 2140 ± 82 | 40 ± 1.80 | 23 ± 1 | 102,000 ± 1760 | 4.6 | −0.24 ± 0.05 | |
| αL210Q | 19 ± 2 | 31 ± 6 | 1.7 | 93 ± 4 | 5180 ± 167 | 56 | NA | NA | 75,600 ± 1950 | 920 ± 40 | 82 ± 4.15 | 25 ± 1 | 119,000 ± 1720 | 4.8 | −0.66 ± 0.06 | |
| αL273F | 63 ± 3 | 1080 ± 104 | 17 | 160 ± 9 | 5680 ± 128 | 36 | 399 ± 36 | 38,300 ± 2202 | 0.01 ± 0.0011 | 81,400 ± 1460 | 739 ± 23 | 110 ± 4.0 | 22 ± 1 | 134,000 ± 2490 | 6.1 | −0.84 ± 0.05 |
| αI274A | 50 ± 55 | 331 ± 400 | 6.6 | 44 ± 6 | 15,800 ± 1800 | 359 | NA | NA | 852 ± 44 | 2150 ± 28 | 0.40 ± 0.021 | 24 ± 2 | 124,000 ± 4520 | 5.2 | 2.46 ± 0.06 | |
| αY277L | 230 ± 13 | 13,300 ± 450 | 58 | 440 ± 740 | 26,600 ± 900 | 60 | NA | NA | NA | 18,100 ± 330 | 4800 ± 56 | 3.8 ± 0.12 | 22 ± 1 | 82,000 ± 2200 | 3.7 | 1.13 ± 0.04 |
Kinetic parameters and error estimates are derived from global fitting of a kinetic scheme to data obtained over a wide range of ACh concentrations (Materials and Methods). Units are μm−1 · s−1 for association rate constants and s−1 for all others. Gating equilibrium constants (θ) are ratios of channel opening (β ) to closing rate (α ) constants. NA, Reaction step not detected. Free energy change Δ G° = −RTln(θmutant/θwild type), where R is the gas constant (1.987 cal/° K/mol) and T is the absolute temperature (295° K).