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Publisher Summary Compounds that inactivate cytochromes P450 in a selective manner require metabolism by the enzyme and are most commonly known as “mechanism-based inhibitors (MBIs)/inactivators,” but they may also be termed as “suicide inhibitors” or “time-dependent inhibitors (TDIs).” The metabolism of a substrate can lead to the inhibition of an enzyme in various ways. While it is theoretically possible for a cytochrome P450 substrate to be metabolized to a form that interacts more potently with the enzyme, there are no clear examples of such an agent. This is likely because the products of metabolism by a cytochrome P450 are generally less hydrophobic than the substrate, and therefore binds less strongly to the enzyme. In addition, recent advances in the understanding of MBIs of cytochromes P450 have provided a framework for the prediction of in vivo effects from in vitro data and have given insight into the biology of the turnover of the proteins. The potent, long-lasting effects of MBIs of enzymes such as CYP3A4 continue to be a liability for some drugs and a positive advantage for others, and therefore a thorough understanding of the mechanism and kinetics of inhibition is important.

Publisher Summary This chapter discusses the antipeptide antibodies in studies of cytochromes P450IA. Antipeptide antibodies directed to specific surface regions of cytochromes P450 provide a powerful means of studying both the structure and function of the members of this super family of proteins. Such antibodies are suitable for many immunological techniques, including enzyme-linked immunosorbent assay (ELISA), immunoblotting, immunocytochemistry, and immunoinhibition of enzyme activity. The generation of antipeptide antibodies is particularly suited to the analysis of cytochromes P450 because the primary structures of many of the members this large group of isoenzymes has been deduced by nucleotide sequencing. In contrast, comparatively few isoenzymes have been purified to homogeneity owing to technical difficulties caused by the hydrophobic nature of cytochrome P450 and the relatively low tissue levels of many of the isoenzymes.