Rate limiting enzyme of purine nucleotide synthesis is :
**Core Concept**
The purine nucleotide synthesis pathway is a critical process in the body, allowing for the production of essential nucleotides for DNA and RNA synthesis. The rate-limiting enzyme in this pathway plays a crucial role in regulating the overall rate of purine nucleotide production. This enzyme is a key target for various regulatory mechanisms, ensuring that purine nucleotide synthesis occurs at the optimal rate.
**Why the Correct Answer is Right**
The correct answer is **Xanthosine Phosphoribosyltransferase (XPT)**, also known as Hypoxanthine-Guanine Phosphoribosyltransferase (HGPRT). This enzyme catalyzes the conversion of hypoxanthine and guanine to their respective monophosphate nucleotides, which are then further converted to diphosphate and triphosphate nucleotides. HGPRT is the rate-limiting step in purine nucleotide synthesis, as it allows for the regulation of the pathway's overall activity. This enzyme is also important in maintaining the balance between purine and pyrimidine nucleotide synthesis.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as it does not specify the correct enzyme responsible for the rate-limiting step in purine nucleotide synthesis.
* **Option B:** This option is incorrect as it refers to an enzyme involved in a different biochemical pathway.
* **Option D:** This option is incorrect as it refers to an enzyme involved in the breakdown of purine nucleotides, rather than their synthesis.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that defects in HGPRT can lead to Lesch-Nyhan syndrome, a rare genetic disorder characterized by excessive uric acid production, intellectual disability, and self-mutilating behaviors. This condition highlights the critical role of HGPRT in maintaining purine nucleotide balance and overall health.
**Correct Answer:** B. Xanthosine Phosphoribosyltransferase (XPT), also known as Hypoxanthine-Guanine Phosphoribosyltransferase (HGPRT).