[Metabolism of xenobiotics: beneficial and adverse effects].

The systems developed by living organisms for the metabolism of xenobiotics play a key role in the adaptation of living species to their chemical environment. Recent data about mammalian cytochrome P450 structures have led to a better understanding of the molecular basis for the adaptability of these enzymes to xenobiotics exhibiting highly variable structures. The action of these enzymes on xenobiotics leads to other beneficial effects such as the bioactivation of some drugs, but also to adverse effects with the formation of aggressive metabolites for the cell that are responsible for the appearance of many toxicities.