Table 1.

Thermodynamic parameters of EF-G binding to GDP and GTP determined by ITC*

SampleLigandT, °CKa, M−1Kd, μMΔH0,§ kcal/molTΔS0, kcal/molΔG0, kcal/mol
EF-GGDP41.4 × 1057.1−5.610.93−6.54
GDP251.1 × 1059.1−5.900.96−6.86
GDP376.0 × 10416.7−6.310.47−6.78
GTP42.8 × 10435.73.749.40−5.66
GTP251.2 × 1058.3−1.705.25−6.95
GTP371.1 × 1059.1−5.142.00−7.14
EFG·GTP**GDP41.8 × 1055.6−6.66
EFG·GTP**GDP376.2 × 10416.1−6.80
EFG·GDP**GTP43.2 × 10431.2−5.71
EFG·GDP**GTP379.1 × 10411.0−7.03
  • *All measurements were performed two to four times in phosphate buffer (5 mM K2HPO4, 10% glycerol, 1 mM DTT, 95 mM KCl, and 5 mM MgCl2, pH 7.5).

  • Ka, affinity constant; standard deviation did not exceed ± 20%.

  • Kd, dissociation constant; calculated as 1/Ka.

  • §Δ H0, enthalpy variation; standard deviation did not exceed ±10%.

  • TΔ S0, entropy variation; calculated from the equation ΔG0 = ΔH0TΔS0.

  • Δ G0, Gibbs energy; calculated from the equation ΔG0 = −RTlnKa.

  • **The model of competitive ligand binding was used (see Materials and Methods and ref. 22).