Localization of 3,5,3'-L-triiodothyronine receptor in rat kidney mitochondrial membranes

Binding of triiodothyronine(T₃) to submitochondrial fractions from rat kidney was studied. Both inner and outer mitochondrial membranes were purified by sucrose gradient centrifugation. Both membranes had specific binding sites for T₃. Scatchard analysis of T₃ binding by membranes gave different affinity constants between inner and outer membranes. In studies with gel filtration of soluble T₃ receptors, four main T₃ binding activities in outer membranes and two main T₃ binding activities in inner membranes were isolated. The results indicate that both inner and outer mitochondrial membranes have specific binding sites for T₃ and that each membrane has a specific structure in T₃ receptor.