Solubilization and characterization of a membrane 3, 3′, 5-triiodo-L-thyronine binding protein from rat pituitary tumor GH 3 cells

Abstract

To understand the mechanism by which T 3 enters cells and carries out its biological functions membrane binding sites for 3, 3′, 5-triiodo-L-thyronine were solubilized from rat pituitary tumor GH 3 cells by detergents. Among three detergents tested, CHAPS is the best in preserving hormonal binding affinity and specificity. Least square analysis of the binding data show one class of binding site with a Kd of (6.35±1.27)nM and Bmax of (0.84±0.056) pmoles/50 μg protein. Hormone binding activity is lost by heating, pronase digestion and in the absence of NaCl. The pH optimum for binding is 7.0 and the binding activity is enhanced by dithiothreitol. The solubilization of membrane-associated thyroid hormone binding proteins will facilitate further characterization and exploration of their biological functions.