Physicochemical properties of 57 kDa thyroid hormone binding protein from rat liver nuclei

The nuclear thyroid hormone binding protein (NTHB) with the molecular weight of 57 kDa was obtained from rat liver nuclear extracts by using HPLC and DEAE-Sephadex A-25 ion exchange chromatography methods. Fluorescein isothiocyanate-labeled 3,5,3'-triiodo-L-thyronine (F-T3) was used as a fluorescent probe to identify the hormone binding protein. Purified NTHB has a single binding site for T3 with the apparent binding constant of (3.3 +/- 0.7) X 10(8) M-1. NTHB is an acidic protein with a pI of 5.0. The secondary structure of NTHB is characterized by about 42% helical and 18% beta-structure from CD measurements.