RESUMO
2,3,7,8-Tetrachlorodibenzo-rho-dioxin (TCDD) binds to a specific, high-affinity, low-capacity protein in rat liver cytosol. The TCDD-receptor complex is a large molecule with a Stokes radius of 6.6 nm as determined by gel filtration on calibrated columns. The receptor complex sediments at 5.0 S on glycerol gradients. The calculated molecular weight from the physical parameters was 136 000 and the frictional ratio 1.79. The TCDD-receptor complex binds to DNA-cellulose without preceding heat activation or incubation at high ionic strength. The receptor must first bind TCDD before it can interact with DNA. The DNA-binding ability can be removed from the TCDD receptor by limited proteolysis with trypsin. This treatment does not affect the TCDD-binding site of the receptor. The proteolytic fragment of the TCDD-receptor complex containing the TCDD-binding site but not the ability to bind to DNA appears to be approximately the same size as the native receptor, as judged from chromatography of Sepharose CL-6B and glycerol gradient centrifugation.
Assuntos
DNA/metabolismo , Dioxinas/metabolismo , Fígado/metabolismo , Dibenzodioxinas Policloradas/metabolismo , Receptores de Droga/metabolismo , Animais , Sítios de Ligação/efeitos dos fármacos , Centrifugação com Gradiente de Concentração , Cromatografia em Gel , Citosol/metabolismo , Masculino , Peso Molecular , Ratos , Receptores de Hidrocarboneto Arílico , Tripsina/farmacologiaRESUMO
The ontogeny of the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) receptor was studied in Sprague-Dawley rats by quantitation of the receptor in liver cytosol using isoelectric focusing in polyacrylamide gel. No differences by sex in the receptor concentration were seen at any of the ages studied. Newborn, 21-day-old, and 42-day-old rats contained significantly more receptor in the liver cytosol than did 56-day-old rats. There was no significant difference in the receptor concentration in liver cytosol from 7-day-old rats compared to that from 56-day-old rats. The maximum receptor concentration was found in cytosol from 21-day-old rats [36.1 +/- 24.0 (S.D.) fmol/mg protein]. Adult rats (56 days old) contained the lowest concentration of receptor (13.3 +/- 6.3 fmol/mg protein). The level of TCDD receptor in liver cytosol from adult rats was not significantly changed by orchiectomy, ovariectomy, adrenalectomy, or hypophysectomy. The maximum for TCDD receptor concentration at puberty corresponds to the reported maximum for the induction of aryl hydrocarbon hydroxylase activity. However, no further conclusion can as yet be drawn concerning the regulation of the TCDD receptor.
