Table I.
Effect of pH on Kinetics and Thermodynamics of Binding PA to CMG2
| PA variant | pH | ka (×104) (M−1 s−1) | kd (×10−5) (s−1) | KDa (M) | EA (kJ mol−1) |
|---|---|---|---|---|---|
| WT | 8 | 2.90 (0.02)b | 4.00 (0.08) | 1.4 × 10−9 | 44.70 (0.07) |
| 8c | 3.00 (0.05) | ||||
| 7.5 | 3.60 (0.02) | 41.00 (0.13) | |||
| 7 | 4.20 (0.01) | 40.20 (0.05) | |||
| 6 | 6.50 (0.02) | 4.60 (0.16) | 7.0 × 10−10 | 30.20 (0.04) | |
| 6c | 5.90 (0.04) | ||||
| 5 | ND | 4.40 (0.08) | ND | 30.00 (0.12) | |
| W346F | 8 | 0.63 (0.03) | 38.40 (0.16) | 6.1 × 10−8 | 51.00 (0.10) |
| 6 | 1.00 (0.05) | 48.30 (0.21) | 4.8 × 10−8 | 23.80 (0.23) | |
| 2FHis | 8 | 3.50 (0.01) | 4.40 (0.08) | 1.3 × 10−9 | 49.20 (0.10) |
| 7.5 | 4.30 (0.02) | 48.20 (0.12) | |||
| 7 | 4.70 (0.02) | 41.50 (0.07) | |||
| 6 | 10.00 (0.004) | 3.10 (0.16) | 3.1 × 10−10 | 41.90 (0.02) | |
| 5 | 37.00 (0.02) | 10.50 (0.16) | 2.8 × 10−10 | 34.70 (0.15) |
a
The equilibrium dissociation constant is calculated from the association and dissociation rate constants according to KD = kd/ka.
b
Error is in parentheses
c
Measured using constant ionic strength conditions: 100 mM Tris/50 mM MES/50 mM Acetic acid.32