Characterization and control of cytosolic binding proteins for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the rat...

The presence of a high-affinity, low-capacity 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) binding complex was demonstrated in cytosol from rat lung. When analyzed by sucrose density gradient centrifugation, the 3H-TCDD binding complex sedimented at 8-9 S and 6.5 S in low and high ionic media, respectively. The apparent dissociation constant (Kd) of the 3H-TCDD binding complex was determined to be 2.9 nM and the number of binding sites (Bmax) was approximately equal to 69 fmol/mg of cytosolic protein. The entity was sensitive to heat and to proteases but not to DNAse or RNAse, indicating that it was a protein. An excess of unlabeled TCDD, benzo[a]pyrene, 3-methylcholanthrene, 7,12-dimethylbenzo[a]anthracene and 9-hydroxy ellipticine all competed with 3H-TCDD for binding. A single injection of either benzo[a]pyrene (20 mg/kg body weight) or 9-hydroxy ellipticine (20 mg/kg body weight) had different effects on the concentrations of 3H-TCDD binding proteins in the lung but none of the chemicals had a significant effect on the synthesis of surfactant as assayed by total phospholipid content, 72 h after the injection.