Isothermal titration calorimetry investigation of the interactions between vitamin B6-derived hydrazones and bovine and human serum albumin

The binding of low molecular weight compounds with the transport proteins of blood is an essential step of their delivery into living cells and thus the accurate investigation of the interactions occurring in solution at physiological conditions is crucial for the development of efficient biologically active molecules. In this work, we report on the complex species, stability constants and thermodynamic parameters for the binding reactions of hydrazones derived from pyridoxal-5ʹ-phosphate (PLP) with bovine and human serum albumin (BSA and HSA) in neutral aqueous solution. The study has been carried out using isothermal titration calorimetry which allowed to directly obtain both binding constant and enthalpy change values for the systems investigated. The thermodynamic characterization in solution revealed that the PLP-hydrazone derivatives are able to effectively interact with both bovine and human serum albumin and enabled the determination of the driving forces for the molecular recognition process. The formation of the 1:1 complex was found to be always enthalpy favored and driven due to the insertion of the hydrazone moieties into the hydrophobic pockets of BSA or HSA.