[A model for the adsorptive distribution of thyroid hormone in the cell (author's transl)]

Mitochondria from rat livers were suspended in solutions of cytoplasmic proteins ("cytosol") containing 0.5--4.7 g total protein per liter suspension. In these suspensions the adsorptive distribution of radioactive 3,5,3'-L-triiodothyronine was studied in the concentration range between 0.04 and 0.50 nmol/1. The experiments show that the distribution of the hormone between the liquid phase of the cytosol and the solid phase of the mitochondria depends mainly on the protein concentrations in both phases. The mathematical formulation of this distribution equilibria which is also applicable to thyroxine corresponded closely with the experimental findings. The processes of the adsorptive binding of thyroid hormones to cell proteins observed in vitro are thought to represent part of a transport chain that exists between different compartments in vivo. The consequences of these considerations on the transport of thyroid hormones within the cell are discussed.