Purification of the mitochondrial triiodothyronine (T3) receptor from rat liver

The thyroid hormone receptor of the inner membrane of rat liver mitochondria was purified by osmotic and freeze-thaw lyses followed by partial purification on Sephadex G-200, and then by affinity chromatography with T3-Sepharose 4B. A single predominant protein band demonstrable on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was present in the first 4 mM NaOH elution peak of affinity chromatography. This was collected from affinity peaks from about 30 rat livers followed by preparative PAGE. A single absorbance peak was observed by high pressure liquid chromatography. The purified protein was analyzed for binding constants, amino acid composition, and characterized by analytical ultracentrifuge. The association constant (KA) exceeded 10(11) M-1. The sedimentation coefficient (S20,w) was 2.2 S, the partial specific volume (v) was 0.72, the frictional coefficient [(f/f0)sM] was 1.68, and the molecular weight was estimated at 28,000. The amino acid composition was obtained.