The interaction of thyroxine with plasma proteins: localization of thyroxine-binding protein in Cohn fractions of plasma.

Recently zone electrophoretic techniques have been employed to characterize the site of thyroxine-binding in plasma (1-7). In most reports, an association has been described between thyroxine and a protein moiety intermediate in electrophoretic mobility at pH 8.6 between the al and the a, globulins. A concentrated source of this thyroxine-binding protein (TBP) has not been available for further purification or for experimental evaluation of its physiological role. To meet these objectives, zone electrophoretic techniques have been employed to localize TBP in subfractions of plasma prepared by Method 6 of Cohn and his co-workers (8, 9).