Allopurinol specifically inhibits which enzyme?
**Core Concept**
Allopurinol is a xanthine oxidase inhibitor used in the management of gout and hyperuricemia. Xanthine oxidase is an enzyme involved in the catabolism of purines, converting hypoxanthine to xanthine and xanthine to uric acid.
**Why the Correct Answer is Right**
Allopurinol specifically inhibits xanthine oxidase by competing with hypoxanthine and xanthine for the active site of the enzyme. This inhibition results in decreased production of uric acid and, subsequently, reduced serum urate levels. The enzyme xanthine oxidase is a flavoprotein that contains molybdenum and iron-sulfur clusters, which are essential for its catalytic activity.
**Why Each Wrong Option is Incorrect**
* **Option A:** Allopurinol does not inhibit xanthine dehydrogenase, a related enzyme that is also involved in purine catabolism but is not the primary target of allopurinol.
* **Option B:** Allopurinol is not a uricase inhibitor, as uricase is an enzyme involved in the breakdown of uric acid to allantoin, which is not the primary target of allopurinol.
* **Option C:** Allopurinol does not inhibit glucose-6-phosphatase, an enzyme involved in glucose metabolism that is not related to purine catabolism.
**Clinical Pearl / High-Yield Fact**
It's essential to note that allopurinol can cause a rare but potentially severe hypersensitivity reaction, requiring prompt recognition and discontinuation of the medication.
**Correct Answer: C. Allopurinol specifically inhibits xanthine oxidase.**