OBSERVATIONS CONCERNING THE BINDING OF THYROID HORMONES BY HUMAN SERUM PREALBUMIN*

Abstract

Electrophoretic and dialysis techniques were employed with serum, cerebrospinal fluid, and a purified preparation. Thyroxine-binding by TBPA (thyroxine-binding pre-albumin) was observed in a variety of organic and inorganic buffers, and was inhibited by salicylates, barbital, and trypan blue. Such inhibition was associated with increased binding of thyroxine in the alpha-globulin zone. Deaminated derivatives of thyroxine and 3,5,3[image]-L-triiodothyroxine were bound by TBPA, but not by TBG (thyroxine binding globulin). The affinity of TBPA for these derivatives was greater for the tetraiodinated than the triiodinated, and for the acetic, rather than the propionic acid, analogues. Previous demonstrations of thyroxine-binding by TBPA during electrophoresis of serum in agar gels at pH 7.4 were confirmed. Evidence has been presented which suggests that thyroxine-binding by TBPA is not demonstrable during paper electrophoresis at pH 7.4 because of a decreased avidity of TBPA for thyroxine and an increase in the binding of thyroxine by filter paper.