The human cytochrome P-450 superfamily is comprised of 57 genes. Cytochrome P-450s use electrons from nicotinamide adenine dinucleotide (NADH) and oxy¬gen to oxidize their substrates. These genes code for enzy¬mes that have a role in many metabolic processes including:
• Metabolism of drugs and foreign chemicals including plant metabolites and environmental contaminants Metabolism of arachidonic acid and eicosanoids Cholesterol metabolism and bile acid biosynthesis Steroid synthesis and metabolism Vitamin D3 synthesis and metabolism Retinoic acid hydroxylation Saturated and unsaturated fatty acids
The cytochrome P-450 acts on many endogenous substrates introducing oxidative, peroxidative, and reduc¬tive changes into small molecules. Cytochrome P-450s metabolize various drugs and natural plant products; environmental chemicals and pollutants are successfully detoxified. These important enzymes are the primary interface between humans and the chemical environment. The actions of these enzymes may produce toxic meta¬bolites, however, that may increase risks of cancer, birth defects, and other toxic effects.
Several P-450s are involved in the metabolism of foreign compounds (xenobiotics) such as drugs, plant-derived or fungal-derived secondary metabolites consumed with food, and thousands of environmental pollutants that include arylamines, halogenated hydrocarbons, herbicides, indus¬trial complex mixtures, ingredients of combustion, pesti¬cides, and polycylic aromatic hydrocarbons.

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