Thyroxine-Binding by Serum and Urine Proteins in Nephrosis. Qualitative Aspects1

Abstract

Sera from 11 patients with nephrotic syndrome were studied with regard to the nature of the proteins which interact with thyroxin. The proteins were labeled by the addition of radio-thyroxin in vitro or, in one patient, by intravenous injection. As in normal serum, thyroxin appeared to interact chiefly with 2 proteins: albumin and an alpha globulin (TBP). There was suggestive evidence that thyroxin interacted to a lesser degree with a 3d protein component having an electrophoretic mobility at pH 8.6 slightly faster than albumin, and possibly with a 4th component characterized by a rapid sedimentation rate. TBP in the nephrotic sera appeared to be identical with normal TBP with respect to electrophoretic mobility at pH 8.6 and pH 4.5, and sedimentation rate in the ultracentrifuge. At low thyroxin concentrations the thyroxin-TBP complex accounted for most of the serum thyroxin. At high thyroxin concentrations, TBP was saturated with thyroxin and the excess thyroxin became associated with albumin. In the presence of low serum albumin concentration, however, conventional zone electrophoresis in filter paper gave rise to an artifact due to adsorption of albumin-bound thyroxin in the globulin zones. The urine in one nephrotic patient contained thyroxine in chiefly combination with TBP, and excess thyroxin added to this urine became associated with albumin.