This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Urea Cycle and Disorders, Subject name: Biochemistry
Source of ammonia in urine - 
Select and explain. 
A. Glutaminase, B. Urease, C. Glutamate dehydrogenase, D. Arginase
A: Glutaminase
Answer: A: Glutaminase 
Explanation: Ans. is 'a' i.e., Glutaminase o In many tissues like liver, kidney and brain, ammonia combines with glutamate to yield glutamine, by the action of glutamine synthase. The brain is a rich source of glutamine synthase and it predominantly detoxifies ammonia by this route.o Glutamine is a nontoxic major transport form of ammonia. The glutamine is transported by blood to liver where deamination (removal of amino group) of glutamine takes place. Glutaminase cleaves glutamine to yield glutamate and free ammonia (ammonium ion). The ammonia is converted by liver to urea.# Formation and secretion ammonia by renal tubular cells maintain acid base balance. Ammonia is formed from glutamine by glutaminase. Excretion of ammonia increases in metabolic acidosis and decreases in metabolic alkalosis.