THERMODYNAMIC PARAMETERS OF BETA-LACTOGLOBULIN AND ALPHA-LACTALBUMIN - A DSC STUDY OF DENATURATION BY HEATING

The thermodynamic parameters of beta-lactoglobulin and alpha-lactalbumin heat denaturation, at acid and neutral pH respectively, were determined by differental scanning calorimetry using heating rates ranging from 2.5 to 15-degrees-C min-1. At the high heating rates, the heat denaturation of bovine beta-lactoglobulin (crystallized three times or obtained by microfiltration) at about 2-3 mM protein concentration, was found to be partly reversible. The corresponding temperatures and enthalpy changes are protein-concentration-dependent. alpha-Lactalbumin, in both free and bound Ca2+ forms, shows total reversibility. The effect of adding Ca2+ to the Ca2+-free form was studied, and the thermodynamic parameters of the transition were determined and compared with published results obtained at lower protein concentrations.