In this study, fluoride was used as a probe to understand how the molecular structure of hemoglobin (Hb), myoglobin (Mb) and horseradish peroxidase (HRP) change upon ligand binding. Through fluoride binding to the heme pocket, we were able to measure the enthalpy change and entropy change of the protein. Based on previous studies from our lab, we have found that the entropy change for fluoride binding to the heme pocket of Mb can vary from 12.5 J K–1mol–1 at pH 5 to +177 J K–1mol–1 at pH 8. Similarly, the entropy change for fluoride binding in Hb increases with an increase in pH. In the present study, we have examined how the presence of CaCl2 and PbCl2 affect the thermodynamic properties of fluoride binding in myoglobin. Based on the current results, the entropy change of fluoride binding in the presence of CaCl2 at pH 5 has been found to be –21 kJ mol–1, while the entropy change of fluoride binding in the presence of PbCl2 has been found to be –23 kJ mol–1. Even in the presence of heavy metals, the entropy change and enthalpy change of fluoride binding shows a strong correlation, known as the entropy-enthalpy compensation. These results contribute to the idea that the entropy-enthalpy compensation is a general behavior of proteins due to the solvation of the globin structure upon ligand binding.

Thermodynamics of fluoride binding in heme proteins in the presence of CaCl2 and PbCl2

2019 Spring National Meeting

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