Physiochemical factors influencing the stability of solubilized liver nuclear receptor-3,5,3'-triiodothyronine complex in vitro.

Nuclear acidic protein fraction containing saturable receptors for thyroid hormones was prepared from purified rat liver nuclei by extraction with 0.3 mol l-1 KCl. The inhibitory effect of an increasing ionic strength on the 3,5,3'-triiodothyronine (T3) binding to receptors at pH 8.0 for 2 h and tested up to 2.0 mol l-1 KCl was confirmed. The nuclear receptor-T3 complex was found resistant to the effect of a higher ionic strength up to 1 mol l-1 KCl when subsequently incubated at pH 8.0 for 1 h. In addition, a rapid dissociation of the receptor-T3 complex at alkaline pH in the order of 10.5 greater than 10.0 greater than 9.0 greater than 8.0 was re-examined. The effect of ATP ranging from 0.05 mmol l-1 to 1.0 mmol l-1 on the stability of the receptor-T3 complex at pH 8.0 was also studied. The experiments were conducted in the presence of 25 mmol l-1 Na2HPO4 in order to suppress the effect of the phosphate groups of ATP molecule by inorganic phosphate. The data confirmed that the concentration of ATP starting from 0.05 mmol l-1 may cause the dissociation of nuclear receptor-T3 complex in vitro.