The binding of mixtures of iodoamino acids and of inorganic iodide by various serum proteins

Abstract

1. 1. Human serum was treated with a thyroid digest prepared from rat thyroids 72 hr. after the animals received a dose of NaI 131. 2. 2. The dialyzed I 131-containing serum proteins were fractionated by diethylaminoethylcellulose ion-exchange chromatography. 3. 3. The composition of the protein fractions was characterized by means of paper electrophoresis. 4. 4. The protein-bound iodo compounds were removed from the proteins and tentatively identified by means of paper chromatography. 5. 5. Thyroxine (T 4), triiodothyronine (T 3), diiodothyronine (T 2), iodide (I −), diiodotyrosine (DIT), monoiodotyrosine (MIT), and diiodohistidine (DIH) were found to be bound to the serum proteins. 6. 6. These iodo compounds were present in many or all of the 16 fractions obtained; however, specific binding sites for T 4 occurred in the α 1-globulins, for T 2 and T 3 in the α 1-globulins and albumins, for iodide in the α-globulins and albumins, for DIT in the fast-moving γ-globulins, for MIT in the basic, slow-moving γ-globulins, and for DIH in the proteins most strongly retained by the cellulose exchanger.