Thermodynamics of the binding of calcium and strontium to bovine α-lactalbumin

AbstractMicrocalorimetry and equilibrium gel filtration were used to determine the thermodynamic functions ΔH°, ΔG° and ΔS° guiding the interaction of Ca2+ and Sr2+ with bovine α-lactalbumin. Two methods of nearly complete metal removal from the protein gave identical results. The single Ca- and Sr-binding site, which has moderate affinity for these ions (Kca = 2.5 × 106 M−1 and KSr = 5.1 × 105 M−1), displays unusually large enthalpy changes of −118 kJ · mol−1 for Ca2+ and −75 kJ·mol−1 for Sr2+. The concomitant reaction entropies equal −273 and −142 J·K−1· mol−1, respectively