Table 1.
Thermodynamic parameters of α1S- and α1R-Na,K-ATPase in E2P-conformation binding to ouabain, digoxin and marinobufagenin (MBG) at pH 7.4 and 37 °C.
| Na,K-ATPase | CTS | Ka, M−1 | Kd, nM | n | ΔH, kcal/mol | TΔS, kcal/mol | ΔG, kcal/mol |
|---|---|---|---|---|---|---|---|
| α1S-Na,K-ATPase | ouabain | 1.9 × 107 | 53 | 0.7 ± 0.2 | −21.6 | −11.3 | −10.3 |
| digoxin | 4.0 × 106 * | 208 | 0.5 ± 0.1 | −7.9 | 2.0 | −9.9 | |
| MBG | 4.3 × 105 * | 2320 | 1.7 ± 0.2 | −5.2 | 2.8 | −7.9 | |
| α1R-Na,K-ATPase | ouabain | 3.1 × 105 * | 3226 | 0.6 ± 0.1 | −4.3 | 3.4 | −7.7 |
| digoxin | nd | nd | nd | ||||
| MBG | nd | nd | nd |
All measurements were performed three times. MBG—marinobufagenin; Ka—association constant, standard deviation did not exceed ±20%; Kd—dissociation constant; calculated as Kd = 1/Ka; n—reaction stoichiometry; ΔH—enthalpy variation; standard deviation did not exceed ±20%; TΔS—entropy variation; standard deviation did not exceed ±20%; * p < 0.01 in comparison with α1S-Na,K-ATPase:ouabain complex Ka; ΔG—Gibbs energy; Calculated from the equation: ΔG = −RTlnKa; nd—not detected.