M Shalbafan - Chemistry Department, Imam Khomeini International University, Qazvin, Iran
G Rezaei Behbehani - Chemistry Department, Imam Khomeini International University, Qazvin, Iran
N Gheibi - Department of Physiology and Medical Physics, Qazvin University of Medical Scienc
D Illghari - Department of Physiology and Medical Physics, Qazvin University of Medical Scienc

lanthanide ions(Ce3+,La3+,Er3+) induced Conformational changes of human serum albumin, HSA, in phosphate buffer 10mM at pH 7.4 are investigated using isothermal titration calorimetry, ITC, UV and fluorescence emission spectroscopic methods. The results indicate that Lanthanide ions induces irreversible denaturation of the HSA structure. These conformational alterations are accompanied by a significant alteration of secondary structures. The UV absorption intensity of theses complexes decreased and a slight blue shift was observed in the absorbance wavelength with increasing ligands concentration. The fluorescence intensity of HSA increased regularly and a slight red shift was observed for the emission wavelength with increasing ligands concentration, indicating that Lanthanides complex could quench the fluorescence of HSA and changes the microenvironment of tryptophan residue. The increasing of emission intensity of HSA indicates loss of the tertiary structure of HSA. The results obtained from ITC data are in satisfactory agreement with the spectroscopic methods. The strong negativecooperativity of ligand binding with HSA recovered from the extended solvation model, indicates that HSA denatured as a result of its interaction with Lanthanide ions.

Human serum albumin, Isothermal titration calorimetry, Fluorescence spectroscopy, UVspectroscopy, Lanthanide ions