Binding equilibrium of I− to serum albumin with resonance Rayleigh scattering

The binding equilibrium between I - and human serum albumin (HSA) or bovine serum albumin (BSA) has been studied by means of the resonance Rayleigh scattering (RRS) and equilibrium dialysis. It has been found for the first time that RRS and multiple frequency scattering (MFS) are enhanced as the I - binding to the HSA and BSA, but fluorescence quenches. The equilibrium dialysis results suggest that the binding of I - to HSA and BSA fits a phase-distribution model other than Scatchard model, and that the order of magnitude of its phase-distribution constant was found to be 104. It is most probable that Cl - or other anion ions influence the binding of I - by changing the ionic strength in the solution. The dialysis at different pH indicates that the binding mechanism is due to the electrostatic forces between the I - and protonated basic amino-acid residues.