Isothermal Titration Calorimetric Studies on the Interactions between Casein Phosphopeptide Monomers and Different Calcium Salts
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Abstract:
In this study, the interactions between β-casein phosphopeptides (1-25) (CPP) and different calcium salts were investigated in the simulated small intestine terminal environment were investigated. Isothermal titration calorimetry (ITC) was used as the analysis method, and thermodynamic parameters, stoichiometric number and affinity constants were used as indicators to evaluate the interactions between different calcium salts and CPP. The results showed that CPP could interact with different calcium salts, and both were spontaneous reactions driven by entropy (pH 8.0, 37 ℃). The main driving force of this reaction was ionic interactive forces. When different calcium salts reacted with CPP, there was no obvious difference in enthalpy change, entropy change and free energy (p>0.05), but there were significant differences in stoichiometric number and affinity constants (p<0.05). The stoichiometric number was higher (3~4) when CPP interacted with calcium gluconate, calcium lactate or calcium chloride, whilst the stoichiometric number was lower (2~3) when CPP interacted with calcium aspartate. In addition, compared with other calcium salts, calcium lactate had the lowest affinity constant for its binding to CPP. A higher number of calcium salt binding to the peptide and a lower binding affinity were beneficial to the absorption of calcium in the small intestine. Therefore, compared with other calcium salts, the binding of CPP with calcium lactate may be more conducive to the absorption of calcium in the small intestine. This study lays a solid foundation for better understanding of the thermodynamic changes and interactions of CPP with different calcium salts in the environment simulating that of the small intestine.
