Etiocholanolone receptor in rat liver and novikoff rat hepatoma cell culture

The binding of tritiated etiocholanolone to rat liver and Novikoff hepatoma cells has been investigated. Cytosols obtained from rat liver and Novikoff hepatoma contain high affinity-low capacity binding macromolecules (K_d = 9.6 × 10^-10 M for rat liver and 1.1 × 10^-9 M for Novikoff hepatoma and the number of binding sites was 64 fmol/mg protein for rat liver and 76 fmol/mg protein for Novikoff hepatoma). Cytosols labelled with [³H]-etiocholanolone had a sedimentation coefficient of 4.6 under low and high salt concentration. Preincubation of rat liver slices and Novikoff hepatoma cells with unlabelled etiocholanolone followed by exchange of nuclear receptor complex with [³H]-etiocholanolone showed the presence of a single peak sedimenting at 4.6 S. Extraction of nuclear receptor peak sedimenting at 4.6 S and identification of the steroid showed that 86% of the radioactivity was associated with etiocholanolone and 14% with 5β-androstane-3α,17β-diol. Competition studies showed that steroids with 5β-H configuration were very effective in displacing etiocholanolone from cytoplasmic receptors while steroids with the 5α-configuration were not. These studies show that etiocholanolone receptor present in mammalian liver is essentially similar to that obtained from chick embryo liver.