THE CYTOCHROME-P-450 SYSTEM IN FISH, AQUATIC TOXICOLOGY AND ENVIRONMENTAL MONITORING

Aquatic toxicology has been defined as the qualitative and quantitative study of adverse or toxic effects of chemicals and other anthropogenic materials on aquatic organisms. The subject also includes the study of transport, distribution, transformation and ultimate fate of chemicals in the aquatic environment. Within this multidisciplinary field of science, studies of the biochemistry and function of biotransformation enzymes in aquatic organisms hold a central role. Metabolism or biotransformation through the phase I (cytochrome P-450 monooxygenase enzymes) and phase II (conjugating enzymes) pathway is a requisite for detoxification and excretion of lipophilic chemicals. In addition, such a transformation is also responsible for the activation of foreign chemicals to the intermediates that ultimately result in toxicity, carcinogenicity, and other adverse effects. The dual role of many of these enzyme systems, being involved in both xenobiotic and endogenous metabolism, furthermore makes interactions between foreign chemicals and physiological processes possible. Lastly, the response of some of these enzyme systems, in particular the cytochrome P-450 IAI subfamily, to organic xenobiotics such as oil hydrocarbons, PCBs, dioxins and dibenzofurans, makes analysis of enzyme levels by catalytic or immunochemical methods a potent way to monitor pollution effects at the molecular level. Several of these aspects will be discussed with special reference to fish.