Use of Thyroxine-Displacing Drugs in Identifying Serum Thyroxine-Binding Proteins Separated by Starch Gel Electrophoresis. ∗

Summary

Serum containing small quantities of radioactive thyroxine (T4-I-131) was subjected to vertical starch gel electrophoresis. Three radioactive peaks were recognized: P1, corresponding to prealbumin 1 in the protein-stained pattern; P2 to the leading two-thirds of the stained albumin band; and P3 to the trailing one-third of albumin and the immediate unstained post-albumin area. Various drugs known to dislodge T4 from specific thyroxine-binding proteins as identified in paper electrophoresis were added to the serum before electrophoresis. Benzylpenicillin and 2,4 dinitrophenol, drugs which displace T4 from thyroxine-binding prealbumin (TBPA) effected a reduction in the radioactivity associated with P1. 5,5 diphenylhydantoin, which displaces T4 from thyroxine-binding globulin (TBG) brought about a reduction in P3. Thus, it was concluded that P1 corresponds qualitatively to TBPA and P3 to TBG.