Most common microsomal enzyme involved in metabolism of xenobiotics is
**Core Concept**
The metabolism of xenobiotics, or foreign substances, in the liver involves a complex interplay of enzymes, including those found in the endoplasmic reticulum. The microsomal enzyme system, specifically the cytochrome P450 family, plays a crucial role in this process.
**Why the Correct Answer is Right**
The correct answer involves the enzyme CYP3A4, a member of the cytochrome P450 family. CYP3A4 is responsible for the metabolism of approximately 50% of all clinically used drugs, making it the most abundant and significant enzyme in the human liver. This enzyme is involved in the phase I metabolism of xenobiotics, where it catalyzes the oxidation of lipophilic substances to more hydrophilic compounds, facilitating their excretion.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specify a particular enzyme involved in xenobiotic metabolism.
* **Option B:** This option is incorrect because, although it refers to a cytochrome P450 enzyme, it is not the most common enzyme involved in xenobiotic metabolism.
* **Option D:** This option is incorrect because it refers to a different class of enzymes, the flavin-containing monooxygenases, which are involved in phase I metabolism but are not as significant as CYP3A4 in xenobiotic metabolism.
**Clinical Pearl / High-Yield Fact**
The cytochrome P450 enzymes, particularly CYP3A4, are known to be induced by certain substances, such as rifampicin and phenobarbital, which can increase the metabolism of co-administered drugs, potentially leading to reduced efficacy.
**Correct Answer: C. CYP3A4**