Table 3.
Thermodynamic parameters of 2OG binding to Arabidopsis thaliana PII in the presence of ATP, SP, or CESP.
| Binding molecule | Kd (μM)* | ΔH (kcal mol-1) | ΔG (kcal mol-1) | TΔS (kcal mol-1) |
|---|---|---|---|---|
| 2OG | ||||
| PII: ATP | 110.7 ± 3.4 | −10.5 ± 0.3 | −6.8 ± 0.4 | −3.6 ± 0.9 |
| PII: ATP + SP | 105.5 ± 2.7 | −9.9 ± 0.4 | −5.9 ± 0.3 | −4.1 ± 1.3 |
| PII: ATP + CESP | 114.1 ± 3.2 | −10.7 ± 0.2 | −7.1 ± 0.6 | −3.7 ± 1.5 |
*Values are means ± SE of six independent samplings. Ligand-complexed PII was in the presence of excess ligand, either 1.0 mm ATP or 2OG. ΔG values were calculated using ΔG = −RT ln Ka = ΔH − TΔS. Values for thermodynamic parameters could not be determined without either 2OG or ATP in presence of each phosphonate analog due to weak binding suggesting that the those compounds cannot replace 2OG in the PII binding site.