Thermodynamics of Mn(2+)-binding to goat alpha-lactalbumin.

By means of reaction calorimetry we measured the apparent enthalpy change, delta Happ, of the binding of Mn(2+)-ions to goat alpha-lactalbumin as a function of temperature. The observed delta Happ can be written as the sum of contributions resulting from a conformational and a binding process. In combination with the thermal unfolding curve of goat alpha-lactalbumin, we succeeded in separating the complete set of thermodynamic parameters (delta H, delta G, delta S, delta Cp) into the binding and conformational contributions. By circular dichroism we showed that NH+4-ions, upon binding to bovine alpha-lactalbumin, induce the same conformational change as do Na+ and K+: the binding constant KappNH+4 equals 98 +/- 9 M-1.