This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
How does hyperammonemia inhibit TCA cycle? 
Select and explain. 
A. By depleting alpha ketoglutarate, B. By depleting oxaloacetate, C. By increasing concentration of alpha ketoglutarate, D. By increasing concentration of oxaloacetate.
A: By depleting alpha ketoglutarate
Answer: A: By depleting alpha ketoglutarate 
Explanation: Build up of cummonemia which occurs in urea cycle disorder or advanced liver disease, inhibits TCA cycle by depleting alpha ketoglutarate.