Re-evaluation of the proposed interrelationship between thyroxine-binding globulin (TBG) and alpha1-antitrypsin (PI)

Human plasma samples of known thyroxine-binding globulin (TBG) and alpha1-antitrypsin (PI) phenotypes have been radiolabelled with 125I-thyroxine and subjected to isoelectric focusing. The TBG phenotypes were identified by autoradiography which was followed by protein staining to identify the PI phenotypes. The variant banding patterns of both TBG and PI were clearly independent and failed to show any interrelationship on either agarose or polyacrylamide gels. However, autoradiography of agarose gels after fixing in sulphosalicylic acid and trichloracetic acid solution produced banding patterns identical to the PI phenotypes obtained by protein staining. This unexpected finding results from the binding of 125I-thyroxine to PI during the acid-fixing process in agarose gels.