Ammonia in brain is trapped by
**Core Concept**
The question is testing the student's knowledge of ammonia metabolism in the brain. Ammonia is a toxic byproduct of amino acid catabolism and must be converted into a less toxic form to prevent neurotoxicity. The brain has a unique mechanism to trap ammonia, which is crucial for maintaining normal brain function.
**Why the Correct Answer is Right**
The brain traps ammonia by converting it into glutamine via the enzyme glutamine synthetase. This enzyme catalyzes the reaction between ammonia and glutamate to form glutamine, which is a non-toxic form of ammonia. This process is essential for maintaining the acid-base balance in the brain and preventing ammonia toxicity. The enzyme glutamine synthetase is present in astrocytes, a type of glial cell in the brain.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the correct enzyme involved in trapping ammonia in the brain. Glutamate dehydrogenase is an enzyme involved in the metabolism of glutamate, but it is not responsible for trapping ammonia.
**Option B:** This option is incorrect because it is not a specific enzyme or mechanism involved in ammonia trapping. Citrate synthase is an enzyme involved in the citric acid cycle, but it is not directly related to ammonia metabolism in the brain.
**Option C:** This option is incorrect because it refers to a type of glial cell, but it does not specify the correct enzyme involved in trapping ammonia. Astrocytes are indeed involved in ammonia metabolism, but the correct enzyme is glutamine synthetase.
**Clinical Pearl / High-Yield Fact**
It is essential for clinicians to understand the mechanism of ammonia trapping in the brain to diagnose and manage disorders such as hepatic encephalopathy, where ammonia levels are elevated.
**Correct Answer:** C. Glutamine synthetase