Physicochemical properties of the triiodothyronine nuclear receptor from tadpole liver, intestine and tail fin

Abstract

The binding of triiodothyronine (T 3) to tadpole liver, intestine, and tail fin nuclei was consistent with a single class of binding sites. The K D for the binding of T 3 to isolated nuclei from the liver (1.02 nM), intestine (1.40 nM), and tail fin (0.831 nM) nuclei were not significantly different. The number of binding sites for T 3 in the nuclei isolated from each tissue were also not significantly different. Sucrose gradient centrifugation of the salt-extracted nuclear T 3-receptor complex revealed that the s 20,w was not significantly different for the complex from the liver (3.7 S), intestine (3.9 S), or tail fin (3.9 S). Similarly, the Stokes radii of the complex from the liver (3.65 nm), intestine (3.84 nm), and tail fin (3.99 nm) were not significantly different. Molecular weights of 57000, 64000, and 67000 were calculated from the sedimentation coefficients and Stokes radii for the T 3-receptor complex from the liver, intestine, and tail fin, respectively. The similarity of the physicochemical properties of the T 3-receptor complex from each of the tissues studied is consistent with the hypothesis that the same receptor is capable of inducing tissue-specific biochemical changes.