The tissue distribution of the receptor protein for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in adult male Sprague-Dawley rats was determined by isoelectric focusing in polyacrylamide gel of cytosol labeled with [3H]TCDD. In order that the TCDD receptor focuses as a single sharp peak at pl 5.2, partial proteolysis of the receptor must first be carried out. The radioactivity bound to this peak was completely displaced when labeling of the cytosol was carried out in the presence of 100-fold unlabeled 2,3,7,8-tetrachlorodibenzofuran.

The highest concentration of the TCDD receptor was found in thymus (25.2 fmol/mg protein; n = 10) and lung cytosol (20.8 fmol/mg protein). No significant difference was seen between the concentration of the receptor in liver (13.9 fmol/mg protein) and kidney cytosol (12.5 fmol/mg protein). Low concentrations of the receptor were found in testis (3.5 fmol/mg protein), brain (2.8 fmol/mg protein), and skeletal muscle cytosol (0.3 fmol/mg protein). No receptor could be detected in the cytosol from pancreas, the adrenal glands, or ventral prostate.

Ventral prostate was found to contain a different binding species for [3H]TCDD than the receptor. This binder focused at pl 4.7. It was not affected by incubation with the same concentration of trypsin used to partially degrade the TCDD receptor. Neither could the prostatic TCDD-binding protein be saturated by incubation in the presence of 100-fold unlabeled 2,3,7,8-tetrachlorodibenzofuran.

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This investigation was supported by grants from LEO Research Foundation and Riksföreningen mot Cancer.

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