THERMODYNAMIC CHARACTERIZATION OF 2 NEARLY SIMULTANEOUS PROTEIN DENATURATIONS

Near-UV circular dichroism and differential scanning calorimetry were used to analyse the thermal denaturation of bovine alpha-lactalbumin a t pH 7.5 and various Ca2+ concentrations. Both analyses revealed that the denaturated protein consists of two fractions, a Ca2+-loaded and a Ca2+-free fraction. Despite this agreement, the two methods afforded significantly different values for the thermodynamic parameters of the denaturations. It was demonstrated that the ellipticity changes were more appropriate than the excess heat capacities for analysis of the t wo types of denaturation. The values of the thermodynamic parameters o btained with the former method are therefore more reliable.