RESUMO
Polycyclic aromatic hydrocarbons (PAHs) are abundant pollutants, and many PAHs are carcinogenic, but only after metabolic activation. Benzo[a]pyrene (BaP) is among the most carcinogenic PAHs. The dose and time response of two enzymes involved in BaP metabolism and the amounts of BaP metabolites excreted into the bile were evaluated in an experiment with dab (Limanda limanda). Ninety dab were exposed orally to one of five doses of BaP (0, 0.08, 0.4, 2, or 10 mg/kg) and sampled at 3, 6, or 12 d after exposure. None of the doses studied caused significant induction of either microsomal ethoxyresorufin-O-deethylase (EROD). which reflects cytochrome P450 1A (CYP1A) activity, or cytosolic glutathione-S-transferase activity (GST). Concentrations of biliary BaP metabolites significantly increased with dose and significantly decreased with time after exposure. It is concluded that biliary BaP metabolites provide a much more sensitive method than EROD (CYP1A) or GST activity to monitor recent exposure to PAHs in dab.
Assuntos
Benzo(a)pireno/metabolismo , Carcinógenos/metabolismo , Linguados/fisiologia , Administração Oral , Animais , Benzo(a)pireno/química , Benzo(a)pireno/farmacocinética , Bile/química , Biomarcadores/análise , Carcinógenos/química , Carcinógenos/farmacocinética , Citocromo P-450 CYP1A1/análise , Citocromo P-450 CYP1A1/farmacologia , Relação Dose-Resposta a Droga , Exposição Ambiental , Monitoramento Ambiental , Glutationa Transferase/análise , Glutationa Transferase/farmacologia , Cinética , Sensibilidade e EspecificidadeRESUMO
The mutant Escherichia coli strain, N4316, has a temperature-sensitive defect in a protein factor required for translation in vitro of bacteriophage f2 RNA. We have purified the normal counterpart of this factor from a wild-type strain, using as an assay its ability to restore the activity of mutant extracts at non-permissive temperature. Our final preparation is free of known initiation, propagation, and release factors, proving that the factor is a new component required for translation. The new factor has a molecular weight of 95000 with preliminary data suggesting a subunit structure. 70% of this protein is found in the soluble-cell fraction, the rest being associated with 70-S ribosomes. Kinetic analyses indicate that the factor acts early in translation. Expression of the defect is highly dependent on the Mg2+ concentration, no temperature-sensitivity being apparent at 15 mM Mg2+. At lower Mg2+ concentrations, the defect is expressed only with natural mRNAs such as f2 RNA, and not with artifical polymers such as poly(U). This specificity suggests that the factor may function in events coded by special sequences in the natural messengers