Effect of pH and guanidine hydrochloride on the conformation of 57 kDa rat liver nuclear thyroid hormone binding protein measured by fluorescence.

The denaturation of the 57 kilodalton (kDa) rat liver nuclear thyroid hormone binding protein (NTHB) by pH and guanidine hydrochloride (GdnHCl) has been investigated with the fluorescence method. The acid and alkaline fluorescence quenching suggests that the structure of NTHB is invariant in the relatively narrow pH region of approximately pH 7-9. A cooperative conformational transition occurred in GdnHCl concentrations of 1.5-2.5 m. The apparent free energy of unfolding of NTHB, delta G(appH2O) was evaluated as 6.31 (+/- 0.12) kcal.mol-1 at pH 7.7, 25 degrees C.