This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Proteins and Amino Acids, Subject name: Biochemistry
Ammonia is toxic to the brain because it leads to depletion of which substrate? 
Select and explain. 
A. Succinate, B. Alpha ketoglutarate, C. Isocitrate, D. Fumarate
B: Alpha ketoglutarate
Answer: B: Alpha ketoglutarate 
Explanation: Ans. B. Alpha ketoglutarateAmmonia reacts with Glutamate to form Glutamine. The Glutamate is formed from alpha keto glutarate an intermediate of TCA Cycle. So alpha ketoglutarate is depleted.