Cytochromes P450 (CYPs) comprise a large superfamily of proteins that are of central
importance in the detoxi fi cation or activation of a tremendous number of natural and syn￾thetic hydrophobic xenobiotics, including many therapeutic drugs, chemical carcinogens,
and environmental pollutants. Some CYPs catalyze the metabolism of endogenous com￾pounds, particularly the ones involved in signaling. CYPs, therefore, are important in medi￾ating interactions between an organism and its chemical environment and in the regulation
of physiological processes. Many CYPs are inducible by the compounds they metabolize. In
addition, genetic polymorphisms of CYP genes affect expression or activity of the enzymes,
which can result in adverse drug reactions or genetic diseases. Consequently, CYPs are
among the most extensively studied groups of proteins, being investigated by researchers in
fi elds as diverse as biochemistry, molecular biology, pharmacology, toxicology, environmen￾tal biology, and genetics. The wide range of techniques that have been applied to the CYPs
re fl ects the diverse backgrounds of the many researchers active in this fi eld.