This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of protein and amino acid, Subject name: Biochemistry
The major source of ammonia in kidney 
Select and explain. 
A. Glutamate, B. Glutamine, C. a-ketoglutarate, D. Alanine
B: Glutamine
Answer: B: Glutamine 
Explanation: Glutamic acid acts as a link between amino acids and ammonia.Ammonia, which is highly toxic, arises in humans primarily from the a-amino nitrogen of amino acids. Tissues, therefore, conve ammonia to the amide nitrogen of the nontoxic amino acid glutamine. Subsequently, in kidney cells, ammonia generated on purpose from glutamine with the help of Glutaminase.Ref: Harper&;s biochemistry; 30th edition; Chapter 28 Catabolism of Proteins & of Amino Acid Nitrogen