Binding of fluoride, bromide and iodide to bovine serum albumin, studied with ion-selective electrodes

The interactions of halide ions, F−, Br− and I−, with bovine serum albumin (BSA) in neutral aqueous solutions (pH=7.1) were investigated by the use of ion selective electrodes. The number of ions bound to BSA was determined from the difference in the amount of ion added to BSA solution and the amount of ion remaining free after equilibration. These data were treated according to the Klotz equation to find the number of binding sites, their equivalency and the binding constants. It was found that BSA has one binding site each for Br− and I−, and two equivalent binding sites for F− in neutral solutions. The rather small number of binding sites for the halides studied was attributed to a net charge of −18 reported in the literature for BSA. The binding constants for Br− and I− and the two stepwise binding constants for F− were also determined.