The unfolding process of apo-human serum transferrin in the presence of cetylpyridinium chloride: an isothermal titration calorimetry study.

Isothermal titration calorimetry (ITC) was utilized at conditions close to physiological (50 mM HEPES buffer, pH 7.4 and 160 mM NaCl) and at various temperatures of 25, 30, 35 and 40 °C to evaluate the thermodynamic parameters, enthalpy and heat capacity changes, and subsequently the unfolding process of apo-human serum tarnsferrin (apo-hTf) in the presence of cetylpyridinium chloride (CPC) as a cationic surfactant. The precise thermograms and heat capacity curves obtained and interpreted in terms of molecular events such as specific and non-specific binding and the unfolding process. The analysis of obtained enthalpograms and heat capacity changes profile showed a distinct extreme region close to [CPC]/[apo-hTf] mole ratio of 20 indicated that predominant cooperative unfolding occurs at this mole ratio via a two states mechanism.