ON MECHANISM OF HORMONE ACTION .5. SUBCELLULAR DISTRIBUTION AND BINDING OF [1,2-H-3)CORTISOL IN RAT LIVER

1. 1. The subcellular distribution of radioactivity in rat liver was investigated 20 min after intraperitoneal injection of 20 and 200 μC of [3H]cortisol per 100 g body wt. The bulk of the liver radioactivity was found in the cytosol fraction and ony 0.2-0.4% was recovered in the purified nuclei. 2. 2. Only 10% of the radioactivity in the cytosol fraction shows RF values similar to that of cortisol in thin-layer chromatography. The major part of this untransformed radioactivity is tightly bound to a macromolecular fraction sedimenting at 4 S. The binding of cortisol to this macromolecule(s) was resistant to ribonuclease but sensitive to proteolytic enzymes and neuraminidase. 3. Virtually all the radioactivity recovered in the salt extracts of purified nuclei was indistinguishable from cortisol by thin-layer chromatography and was found to be weakly associated with a macromolecular fraction in a form resistant to nucleases but sensitive to pronase, trypsin and neuraminidase. At low salt concentrations, this macromolecule(s) shows a sedimentation constant between 8 and 10 S and tends to associate with DNA. AT 0.3 M NaCl the interaction with DNA is weakened and the macromolecule(s) dissociates to give a second component sedimenting at 4 S. 4. 4. The significance of these findings in connection with the initial effect of cortisol on the liver cell, in vivo and in vitro, is discussed. © 1969.