Question

Identify the pair of enzymes which plays an important role in the urinary buffer system in maintenance of acid-base balance.
A. Glutaminase and Adenyl Cyclase
B. Glutaminase and Transaminase
C. Carbonic Anhydrase and Transaminase
D. Carbonic Anhydrase and Glutaminase
Choose the correct answer from the options given below:

• A. B and C only
• B. A only
• C. D only
• D. A, B and D only

Hint:

Ammoniagenesis via renal glutaminase is the primary adaptive mechanism the kidneys use to increase acid excretion during chronic metabolic acidosis.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The kidneys maintain systemic acid-base balance by reabsorbing filtered bicarbonate (\(HCO_3^-\)) and excreting hydrogen ions (\(H^+\)) into the urine.
Because free hydrogen ions would lower urinary pH to damaging levels, excreted protons must be buffered in the tubular lumen, primarily by the phosphate and ammonia buffering systems.

Step 2: Detailed Explanation:
The maintenance of this renal buffering and acid-base regulation relies on two key enzymes:
Carbonic Anhydrase (CA): This enzyme catalyzes the reversible hydration of carbon dioxide to carbonic acid (\(H_2CO_3\)), which dissociates into \(H^+\) and \(HCO_3^-\).
In proximal tubule cells, this reaction provides the protons excreted into the lumen and generates the bicarbonate reabsorbed into the blood.
Glutaminase: This mitochondrial enzyme in renal tubular cells catalyzes the deamination of glutamine to glutamate and ammonium (\(NH_4^+\)).
The production of ammonium serves a dual purpose: it generates new bicarbonate ions for the systemic circulation, and the secreted ammonia (\(NH_3\)) acts as an luminal buffer by binding free protons to form ammonium (\(NH_4^+\)), which is then excreted in urine.
Together, Carbonic Anhydrase and Glutaminase are critical for renal acid excretion and bicarbonate regeneration.

Step 3: Final Answer:
The pair of enzymes that play an important role in the urinary buffer system is Carbonic Anhydrase and Glutaminase (D only).