Table 1.
Thermodynamic and kinetic parameters for TT–RR binding in Mg2+
| Temp. (°C) | Ka (M−1) × 105 | ΔG°obs (kcal/mol) | ΔH°obs (kcal/mol) | TΔS°obs (kcal/mol) | kon (M−1s−1) | koff (s−1) × 10−5 |
|---|---|---|---|---|---|---|
| 0.3 mM MgCl2 | ||||||
| 10 | –a | –a | −20.5 (±3.3) | –a | 200 (±80) | 3.2 (±1.3) |
| 20 | 18 (±5) | −8.4 (±0.4) | −21.9 (±5.0) | −13.6 (±5.2) | 270 (±60) | 13 (±10) |
| 30 | 5.6 (±1.3) | −8.0 (±0.3) | −26.9 (±4.2) | −19.0 (±4.0) | 510 (±210) | 87 (±13) |
| 0.5 mM MgCl2 | ||||||
| 2 | – | – | −20.7 (±4.1) | – | 310 (±180) | 0.4 (±0.5) |
| 5 | – | – | −19.6 (±2.1) | – | 420 (±60) | 1.0 (±0.1) |
| 10 | – | – | −17.8 (±2.7) | – | 600 (±140) | 3.3 (±0.7) |
| 15 | – | – | −19.6 (±3.9) | – | 630 (±410) | 6.4 (±6.2) |
| 20 | 64 (±7) | −9.1 (±0.2) | −18.9 (±2.0) | −9.8 (±2.0) | 940 (±80) | 16 (±4) |
| 30 | 24 (±1) | −8.9 (±0.1) | −23.2 (±1.9) | −14.3 (±1.9) | 1530 (±120) | 62 (±7) |
| 0.7 mM MgCl2 | ||||||
| 10 | – | – | −20.5 (±3.0) | – | 1240 (±30) | 1.7 (±0.1) |
| 20 | 160 (± 4) | −9.7 (±0.1) | −24.8 (±3.2) | −15.1 (±3.2) | 2360 (±60) | 14 (±1) |
| 30 | 56 (± 2) | −9.4 (±0.1) | −22.4 (±3.1) | −13.1 (±3.1) | 3130 (±550) | 58 (±8) |
| 1.0 mM MgCl2 | ||||||
| 5 | – | – | −19.4 (±3.0) | – | 1690 (±270) | 0.7 (±0.1) |
| 10 | – | – | −18.4 (±2.2) | – | 2230 (±210) | 2.2 (±0.2) |
| 15 | – | – | −18.9 (±3.7) | – | 3180 (±630) | 6.7 (±1.3) |
| 20 | – | – | −19.5 (±2.3) | – | 3950 (±540) | 15 (±2) |
| 25 | – | – | −23.6 (±4.7) | – | 5660 (±4890) | 57 (±42) |
| 30 | – | – | −21.3 (±2.1) | – | 5800 (±580) | 68 (±6) |
| 35 | 55 (±7) | −9.5 (±0.2) | −23.9 (±3.0) | −14.3 (±3.1) | 6810 (±1510) | 120 (±20) |
| 40 | 23 (±5) | −9.1 (±0.3) | −26.7 (±3.7) | −17.5 (±3.8) | 7840 (±2060) | 310 (±50) |
| 45 | 9.9 (±2.1) | −8.7 (±0.3) | −28.6 (±5.5) | −19.9 (±5.8) | – | – |
– not determined because ITC c-value greater than 200
–a not determined because post-injection decay too slow to accurately integrate throughout titration