Table 3.
Thermodynamic parameters for Ca2+ binding to nmGCAP2 in the absence (top) and in the presence of 1-mM Mg2+ after fitting ITC data to a two sequential binding site model (mean ± SD, n = 3–4)
nmGCAP2 Ca2+ titration (2-site model) | |||||
---|---|---|---|---|---|
Apparent dissociation constant KD |
Enthalpy change ΔH (kcal/mol) |
Entropy change −TΔS (kcal/mol) |
|||
KD1 (nM) | KD2 (nM) | ΔH1 | ΔH2 | −TΔS1 | −TΔS2 |
No Mg2+ | |||||
35.2 ± 10.4 | 500.5 ± 273.5 | −2.1 ± 0.2 | −0.05 ± 0.31 | −8.1 ± 0.3 | −8.6 ± 0.6 |
With 1-mM Mg2+ | |||||
109.3 ± 95.5 | 2.1 ± 0.6 | −2.5 ± 0.2 | −2.4 ± 0.5 | −7.1 ± 0.7 | −5.4 ± 0.6 |