Detection and characterization of a novel hepatic 8 S binding protein for benzo[a]pyrene distinct from the Ah receptor.
Using fractionation procedures such as sucrose gradient sedimentation and gel permeation chromatography, a novel cytosolic binding protein for benzo[a]pyrene has been detected in liver of nonmammalian and mammalian species including human. This protein, called 8 S protein, cosediments with the Ah receptor after centrifugation in sucrose density gradient but can be separated from the Ah receptor and 4 S protein by gel permeation chromatography. Owing to its binding characteristics, the 8 S protein is clearly distinct from the Ah receptor. The [3H]BP binding parameters have been determined by saturation experiments. According to Scatchard and Woolf plots the Kd are 268 nM and 138 nM for DBA/2 mouse and guinea pig 8 S proteins, respectively. Bmax are 248 and 840 pmol/mg for DBA/2 mouse and guinea pig 8 S proteins, respectively. Apparent molecular mass of 8 S protein, according to Stokes radius (5 +/- 0.2 nm) and sedimentation coefficient, was estimated approximately 170,000 +/- 6000. After in vitro incubation of 8 S proteins with [3H]BP the charcoal, as well as the 4 S protein, exerts potent stripping effects on the [3H]BP binding. In contrast, after administration of [3H]BP to DBA/2 mice the 8 S protein-[3H]BP complex formed in vivo is more resistant to the stripping effects of charcoal and 4 S protein. Competition studies demonstrate that polycyclic aromatic hydrocarbons (PAHs) (BP > 1-aminopyrene > pyrene > 7,12-dimethylbenz[a]anthracene > 3-methylcholanthrene > benzo[e]pyrene > benzo[g, h, i,]perylene) are the best ligands of the 8 S protein. In contrast, the 2,3,7,8-tetrachlorodibenzo-p-dioxin is a poor ligand of this protein. Phenobarbital, steroid hormones, and omeprazole don't bind the 8 S protein. The at present unknown function of the 8 S protein and its role in the toxicology of PAHs are currently under investigation.
Laboratoire de Pharmacologie et Toxicologie, Institut National de la Recherche Agronomique, Toulouse, France.
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Lesca
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Peryt
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Soues
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Maurel
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Cravedi
D000818:Animals; D001564:Benzo(a)pyrene / Q000378:metabolism*; D001667:Binding, Competitive; D002499:Centrifugation, Density Gradient; D003600:Cytosol / Q000737:chemistry; D006168:Guinea Pigs; D006801:Humans; D008099:Liver / Q000737:chemistry*; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D011485:Protein Binding; D018336:Receptors, Aryl Hydrocarbon; D011955:Receptors, Drug / Q000737:chemistry / Q000378:metabolism*; D013045:Species Specificity
D018336:Receptors, Aryl Hydrocarbon; D011955:Receptors, Drug; D001564:Benzo(a)pyrene