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Cytochrome P450 3A4 (abbreviated CYP3A4) (), is an important enzyme in the body, mainly found in the liver and in the intestine. Its purpose is to oxidize small foreign organic molecules (xenobiotics), such as toxins or drugs, so that they can be removed from the body. While many drugs are deactivated by CYP3A4, there are also some drugs which are ''activated'' by the enzyme. Some substances, such as grapefruit juice and some drugs, interfere with the action of CYP3A4. These substances will therefore either amplify or weaken the action of those drugs that are modified by CYP3A4. CYP3A4 is a member of the cytochrome P450 family of oxidizing enzymes. Several other members of this family are also involved in drug metabolism, but CYP3A4 is the most common and the most versatile one. Like all members of this family, it is a hemoprotein, i.e. a protein containing a heme group with an iron atom. In humans, the CYP3A4 protein is encoded by the CYP3A4 gene. This gene is part of a cluster of cytochrome P450 genes on chromosome 7q21.1. == Function == CYP3A4 is a member of the cytochrome P450 superfamily of enzymes. The cytochrome P450 proteins are monooxygenases that catalyze many reactions involved in drug metabolism and synthesis of cholesterol, steroids, and other lipids components. The CYP3A4 protein localizes to the endoplasmic reticulum, and its expression is induced by glucocorticoids and some pharmacological agents. This enzyme is involved in the metabolism of approximately half the drugs that are used today, including acetaminophen, codeine, ciclosporin (cyclosporin), diazepam, and erythromycin. The enzyme also metabolizes some steroids and carcinogens. Most drugs undergo deactivation by CYP3A4, either directly or by facilitated excretion from the body. Also, many substances are bioactivated by CYP3A4 to form their active compounds, and many protoxins being toxicated into their toxic forms ''(for examples - see table below)''. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「CYP3A4」の詳細全文を読む スポンサード リンク
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