Purification of cytosolic 3,5,3′-triiodo-L-thyronine(T 3)-binding protein(CTBP) which regulates nuclear T 3 translocation

Abstract

The NADPH-dependent cytosolic 3,5,3′-triiodo-L-thyronine(T 3)-binding protein(CTBP) was purified from rat kidney using Mono Q-Sepharose, Red sepharose and T 3 affinity chromatography. CTBP which was partially purified by Red Sepharose column chromatography was adsorbed to T 3 affinity column in the presence of 50 uM NADPH. The CTBP was eluted from the gel with the buffer which did not contain NADPH. One molecule of the purified CTBP(58 kDa) bound one molecule of T 3 with 2.44×10 9M −1 of affinity constant. The purified CTBP was activated not only by NADPH but also by NADP in the presence of dithiothreitol. The NADPH-activated form did not transfer T 3 to nuclei, whereas NADP transformed the NADPH-activated CTBP to active form which was able to transfer T 3 to nuclei. These results suggested that CTBP-dependent transport of T 3 to nucleus is controlled by NADPH and NADP.