THE ASSOCIATION OF I131-LABELLED THYROXINE AND TRIIODOTHYRONINE WITH SERUM PROTEINS AFTER STARCH GEL ELECTROPHORESIS

The binding of I131-labelled triiodothyronine (T3) and 1-thyroxine (T4) with the proteins of human serum has been investigated by means of vertical starch gel electrophoresis in borate buffer at pH 8.6. T3 was found to bind largely to thyroxine-binding globulin (TBG) with very little association with albumin, whereas T4 was associated with TBG, albumin, and thyroxine-binding prealbumin (TBPA). Sera from normal persons were shown to have binding capacities for added thyroxine of 25 μg T4 per 100 ml for TBG, and 40 μg T4 per 100 ml for TBPA.