Metabolic bioactivation reactions potentially related to drug toxicities.

The majority of metabolic transformations that xenobiotics undergo in mammalian systems leads to more polar and, in general, less pharmaco-logically and toxicologically potent products. This generalization has led to the proposal that evolutionary factors influencing the emergence of the principal enzymes responsible for the biotransformations of xenobiotics have a link to the improved survival potential of those individuals equipped with enzyme systems capable of converting otherwise toxic substances produced by plantand animal-based food sources to nontoxic metabolites (Jakoby and Ziegler 1990).