Comparative analysis of chemical and thermal denatured 13-lactoglobu1in A in the presence of sugar osmolytes

Chemical denaturation and thermal denaturation of13-lactoglobulin A (f3 — lgA) in the absenceand presence of various concentrations sugar osmolytes and polyols were measured bymonitoring changes in the absorption coefficients at pH 2.0. It has been observed that AGD°(H20), (Gibbs free energy change in absence of denaturant at 25 °C) of f3-1gA in the presenceof 10% (w/v) Trehalose, Sucrose, Sorbitol and Mannitol is increased. We report that thefunctional dependence of AGD°, (Gibbs free energy change at 25 °C) of protein in the absenceand the presence of sugar osmolytes on denaturant concentration is linear. Trehalose is foundto induce remarkable stability of 13-1gA against chemical denaturation. The values of Tm(midpoint of denaturation), AHm (enthalpy change at Tm), and ACp (constant-pressure heatcapacity change) under a given solvent condition were measured. It has been observed thateach sugar stabilizes the protein in terms of Tm and AGD°.