Table 1. Binding cooperativity of melibiose and Na+ to MelBSt.
Parameter | Na+ binding (NaCl in syringe) | Melibiose effect on Na+ binding | Melibiose binding (melibiose in syringe) | Na+ effect on melibiose binding | ||
---|---|---|---|---|---|---|
No sugar (n = 4) | With melibiose (n = 2) | No NaCl (n = 3) | With NaCl (n = 5) | |||
Apparent Kd (mM) or affinity increase | 0.64 ± 0.02a | 0.08 ± 0.01 | 8-fold | 9.28 ± 0.23 | 1.09 ± 0.06 | 8.5-fold |
ΔG or ΔΔG (kJ/mol) | −18.24 ± 0.08 | −23.52 ± 0.13 | −5.28 (P < 0.05)b | −11.60 ± 0.06 | −16.93 ± 0.14 | −5.33 (P < 0.05) |
ITC data were collected at pH 7.45 and 25°C with MelBSt in sample cell as described in Materials and methods. ΔG, binding free energy; ΔΔG, thermodynamics coupling free energy. n = number of test from a total of 5 different batches of MelBSt purification.
Standard error (SEM).
Unpaired t test.