This is one of the most common enzymes found in the cytochrome P450 mixed-function oxidase system, called CYP3A4. The P450 family of proteins is responsible for the metabolism of various compounds within the body such as drugs.  CYP3A4 is a really good model enzyme for this system because it is abundant in the liver where almost all detoxification occurs, however it is also found in the brain and other organs as well. This picture clearly shows the complex form of this protein and also gives a good view of the heme prosthetic group in the middle. This enzyme is the foundation for why toxic compounds do not build up in the body when pharmaceuticals are introduced.