In this work, the influence of the hydrophobic effect on protein stability was studied, specifically using hen egg-white lysozyme (HEWL) as a model protein. Two experimental techniques were employed: circular dichroism (CD) and differential scanning calorimetry (DSC), which were used to analyze the thermal stability of lysozyme under various conditions – in regular water (H₂O), deuterated water (D₂O), and in the presence of different salts (NaBr, CaCl₂, and Na₂CO₃).
The results are consistent with the Hofmeister series and the thermodynamic principles of protein unfolding. CD and DSC measurements showed that changes in secondary structure and thermodynamic parameters (enthalpy, entropy, free energy) are largely influenced by the solvent and the ions present. The presence of deuterated water consistently increased the thermal stability of the protein, confirming the greater strength of hydrophobic interactions compared to regular water. The influence of ions, on the other hand, depends on their hydration capacity.
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