Characterization of thyroxine-albumin binding using high-performance affinity chromatography. II. Comparison of the binding of thyroxine, triiodothyronines and related compounds at the warfarin and indole sites of human serum albumin.

High-performance affinity chromatography was used to examine the binding of thyroid hormones and related compounds at the warfarin and indole sites of human serum albumin (HSA). This was studied by continuously applying L-triiodothyronine (L-T3), L-reverse triiodothyronine (L-rT3) or structural analogs of these compounds to an immobilized HSA column while making injections of site-specific probe molecules (i.e. R-warfarin and L-tryptophan). The results were compared with those obtained previously for L-thyroxine (L-T4). Equilibrium association constants and thermodynamic parameters measured by this approach showed good agreement with previous models reported for L-T4 and L-T3 at their high-affinity sites on HSA. This data confirmed that the phenol groups of L-T4 and L-T3 played a significant role in the binding of these compounds at the indole site. Work performed at the warfarin site and with other solutes (e.g. L-rT3) indicated that additional factors, such as interactions through the thyronine backbone or terminal amine and carboxyl groups of these compounds, could also be involved in the binding of thyroid hormones to HSA.