Thermodynamics of the Ca2+ binding to bovine alpha-lactalbumin.
Bovine alpha-lactalbumin contains one strong Ca2+-binding site. The free energy (delta G0), enthalpy (delta H0), and entropy (delta S0) of binding of Ca2+ to this site have been calculated from microcalorimetric experiments. The enthalpy of binding was dependent on the metal-free bovine alpha-lactalbumin concentration. At 0.8 mg ml-1, metal-free bovine alpha-lactalbumin delta H0 was -110 +/- 6 kJ mol-1. At this concentration the binding constant was estimated from a mathematical analysis of the titration curves to be greater than 10(7) M-1. This means that delta G0 is smaller than -40 kJ mol-1 and delta S0 is less negative than -235 J.K-1 mol-1. The binding of Ca2+ is therefore enthalpy-driven. From binding experiments as a function of temperature, a delta Cp value of -4.1 kJ.K-1 mol-1 was calculated. This value is dependent on the protein concentration. A tentative explanation for this large value is given.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002151:Calorimetry; D002417:Cattle; D007700:Kinetics; D007768:Lactalbumin / Q000378:metabolism*; D011485:Protein Binding; D013816:Thermodynamics
D007768:Lactalbumin; D002118:Calcium