Effect of inorganic anions on the binding of thyroxine by bovine serum albumin.

The fluorescence method was used to investigate the effect of inorganic anions, SCN-, I-, ClO4- and Br- on the binding of thyroxine (T4) by bovine serum albumin (BSA). The apparent binding constants were evaluated in 0.1M sodium phosphate buffer, pH 7.4 at 25 degrees C containing various concentrations of the anions up to 0.15M. Their values decreased at high anion concentrations. The effectiveness of anions in reducing T4 binding was in the following order: SCN- > I= > ClO4- > Br-. Thermodynamic parameters determined in the presence of 0.1M SCN- suggested that the hydrophobic interaction between T4 and BSA could be reduced by these inorganic anions.