Cytochrome P 450
A superfamily of hundreds of closely related Hemeproteins found throughout the phyloGenetic spectrum, from Animals, Plants, Fungi, to Bacteria. They include numerous complex Monooxygenases (Mixed Function Oxygenases). In Animals, these P-450 Enzymes serve two major functions: (1) biosynthesis of Steroids, Fatty Acids, and Bile Acids; (2) Metabolism of endogenous and a wide variety of exogenous substrates, such as toxins and Drugs (Biotransformation). They are classified, according to their sequence similarities rather than functions, into CYP Gene Families (>40% homology) and subFamilies (>59% homology). For example, Enzymes from the CYP1, CYP2, and CYP3 Gene Families are responsible for most drug Metabolism.