This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Urea cycle, Subject name: Biochemistry
Which intermediate of citric acid cycle is used in detoxification of ammonia in brain? 
Select and explain. 
A. Citrate, B. Succinate, C. Alpha-ketoglutarate, D. Oxalo-acetate
C: Alpha-ketoglutarate
Answer: C: Alpha-ketoglutarate 
Explanation: When ammonia is present in body in large amount (hyperammonemia), then this alpha-ketoglutarate of TCA combines with one amino group to form glutamate Fuher glutamate combines with the second amino group to form glutamine Glutamine is a safe form of ammonia storage & transpo. Alpha-ketoglutarate is depleted, which affects TCA cycle. That's why brain is affected as the first organ (Brain is highly aerobic tissue).