Stabilization, accurate determination, and purification of rat liver nuclear thyroid hormone receptor

Rat liver nuclear thyroid hormone receptor lost 3.5.3'-tri-iodo-L-thyronine (T3)-binding activity with a half-life of 14 days, 4h, 139 min, 62 min, 16 min or 6 min at 0, 36, 38, 40, 43 or 45 degrees C respectively, when present in crude nuclear extracts. Glycerol increased the half-life of the receptor during heat inactivation. Protection was reversible by removing the glycerol. The receptor was unstable at a pH below 6.0 or above 10.0. We also found a loss of the receptor activity during the separation of bound and free hormone using the resin test. Of several conditions tested for the separation of bound and free hormone, the addition of heated nuclear extract gave the most accurate estimation of bound hormone when using the resin test. Using these characteristics of the receptor, we purified the receptor to 1220 pmol T3-binding capacity/mg protein with a final yield of 14.6 micrograms/4 kg rat liver.