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
The amino acid producing (a major source of) ammonia in the kidney is 
Select and explain. 
A. Glutamine, B. Alanine, Aspartate, C. Methionine, D. Glycine
A: Glutamine
Answer: A: Glutamine 
Explanation: Formation and secretion ammonia by renal tubular cells maintain acid-base balance. Ammonia is formed from glutamine by glutaminase.