Thyroxine Binding Properties of Glycosylated Human Serum Albumin as Measured by Fluorescence

Abstract

Thyroid hormone, thyroxine (T₄) binding to glycosylated human serum albumin (G-HSA), and native human serum albumin (HSA) were studied as a function of pH using the fluorescence method. T₄ binding affinity for G-HSA was remarkably reduced in an alkaline pH as compared with the native HSA. The thermodynamic parameters for binding are estimated at pH 7.5 : (a) for G-HSA, ΔG=-8.50±0.04 kcal mol^-1 (30°C), ΔH=-5.2 kcal mol^-1, ΔS=+11 e. u. ; (b) for HSA, ΔG=-8.89±0.04 kcal mol^-1 (30°C), ΔH=-3.5 kcal mol^-1, ΔS=+18 e. u. These results suggest that the glycosylation of HSA causes a variation in the electrostatic interaction between T₄ and HSA.