This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of carbohydrate, Subject name: Biochemistry
Hyperammonemia impairs Citric acid cycle by depleting 
Select and explain. 
A. Pyruvate, B. a-ketoglutarate, C. Oxaloacetate, D. Succinate
B: a-ketoglutarate
Answer: B: a-ketoglutarate 
Explanation: Hyperammonemia, as occurs in advanced liver disease, leads to loss of consciousness, coma, and convulsions as a result of the impaired activity of the citric acid cycle, leading to reduced formation of ATP. Ammonia both depletes citric acid cycle intermediates (by withdrawing a-ketoglutarate for the formation of glutamate and glutamine) and also inhibits the oxidative decarboxylation of a-ketoglutarate. Reference: Harper; 30th edition; Page no: 161