MEMBRANE RECEPTION OF THYROID-HORMONES

A comparative investigation was made of the parameter of binding of thyroid hormones - thyroxine (T4) and triiodothyronine (T3) - to highly purified plasma membranes of rat liver, brain, and lung cells. The time, temperature, and concentration dependences of the binding of the hormones were studied, competitive analysis was conducted, and the influence of trypsin and partial delipidation on the parameters of the binding of thyroid hormones was investigated. The presence of two binding sites for thyroid hormones on the plasma membranes of cells of all the investigated tissues was established. Maximum binding of T4 by liver membranes and maximum binding of T3 by rat brain membranes were noted; higher affinity for triiodothyronine in comparison with thyroxine was observed in all the experiments. An important role is suggested both for the protein and for the lipid components of the plasma membranes in the membrane reception of thyroid hormones.