ON THE PARTIAL REVERSIBILITY OF THE BETA-LACTOGLOBULIN HEAT DENATURATION

The thermal behavior of beta-lactoglobulin (beta-lg) dispersed in distilled water (pH = 3.2) is studied by differential scanning calorimetry (DSC) in the temperature range 20-degrees-C-120-degrees-C and within a concentration region of 3.5% to 24%. Recently [1] we have determined by DSC the kinetic parameters for the heat-denaturation of beta-lg. The effect of the protein concentration and of the thermal treatment on transition temperature (T(trs)), half-widths of the peak (DELTA-T1/2), of apparent enthalpy changes (DELTA-appH) and of Van't Hoff enthalpies (DELTA-VHH) have been examined for the concentrations of 8.8% and 24%. In this study we have undertaken complementary experiments for the concentrations 3.5% and 10.8%. The half-widths of the peaks, which depend on the cooperativity of the denaturation process [2], decrease with increasing concentration. The ratio DELTA-appH/DELTA-VHH tends to 1, with low values of the protein concentration and with high scanning rates. This implies the hypothesis of a reversible step for the denaturation process of beta-lg.