Microcalorimetric studies on the interactions of lanthanide ions with bovine serum albumin

The interactions of lanthanide ions (Ln(3+)) with bovine serum albumin (BSA) under mimetic physiological conditions (310.15 K, pH 6.7, 0.1 M NaCl) were studied by microcalorimetry. For the first time, based on Two Sets of Independent Sites Model, molar enthalpies (Delta(r) H-m1, Delta(r) H-m2) and coordination number (n(1), n(2)) of the two sets of binding sites with different affinity were obtained directly from the microcalorimetric results. It was shown that the interactions are endothermic and entropy-driving processes. By combining with fluorescence spectroscopy, other thermodynamic parameters (Delta(r)G(m1), Delta S-r(m1)) were determined for high-affinity specific sites.