Electrophoretic Method for Characterizing Thyroid Function

VIRTUALLY all the thyroxine (T4) in plasma circulates in association with various carrier proteins.1 2 3 4 The electrophoretic identity of these proteins depends upon experimental conditions, however, and herein lay the basis of a controversy that has surrounded efforts to characterize the "physiologic" carrier proteins. An inter-alpha globulin (the thyroxine-binding globulin, or TBG) is generally conceded to be the major thyroxine carrier; the albumin fraction shows a lesser but consistent role in thyroxine transport. The demonstration of a prealbumin carrier by Ingbar5 (thyroxine-binding prealbumin, or TBPA) has generated some discussion3 , 6 , 7 since this fraction shows no affinity for thyroxine when a . . .