Xenobiotic metabolizing enzymes in fish: diversity, regulation and biomarkers for pollutant exposure.

Cytochromes P450 play key roles in biotransformation of pollutant chemicals and in the activation or inactivation of many toxic or carcinogenic compounds. Multiple P450 isozymes have been purified from different fish species. Fish monooxygenase activity shows temperature compensation and sex-related variation. Several xenobiotics can induce cytochrome P450 monooxygenases altering toxicity of chemical contaminants. Polycyclic aromatic hydrocarbons can increase transcription of CYP1A gene in fish as it has been observed in mammals, but phenobarbital-type agents do not induce in fish at all. The presence of conjugation enzymes in fish has also been proved, although their induction by xenobiotics is poorly investigated. Since exposure of fish to environmental contaminants can result in the induction of specific cytochrome P450 enzymes, monitoring of their catalytic activities can identify polluted areas.