Which two enzymes of the urea cycle are located inside the mitochondrial matrix?

• A Carbamoyl phosphate synthetase-II and ornithine transcarbamylase
• B Argininosuccinate synthetase and argininosuccinate lyase
• C Ornithine transcarbamylase and arginase
• D Carbamoyl phosphate synthetase-I and ornithine transcarbamylase ✓

Explanation

The first two steps, catalyzed by carbamoyl phosphate synthetase-I and ornithine transcarbamylase, occur in the mitochondrial matrix using ammonia delivered from glutaminase and glutamate dehydrogenase. The remaining three steps proceed in the cytosol. Option A is the trap because carbamoyl phosphate synthetase-II is a cytosolic pyrimidine-pathway enzyme that uses glutamine, not free ammonia, as its nitrogen donor.

Reference: Lippincott's Illustrated Reviews: Biochemistry, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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