Which two reactions of the urea cycle occur inside the mitochondrial matrix?

• A Argininosuccinate synthetase and lyase reactions
• B CPS-I reaction and ornithine transcarbamylase reaction ✓
• C Ornithine transcarbamylase and arginase reactions
• D CPS-I reaction and argininosuccinate synthetase reaction

Explanation

Carbamoyl phosphate synthetase I and ornithine transcarbamylase are mitochondrial matrix enzymes; carbamoyl phosphate then condenses with mitochondrial ornithine to form citrulline, which exits via the citrulline transporter. The remaining three reactions (synthetase, lyase, arginase) are cytosolic. This compartmentalization explains why OTC deficiency, a mitochondrial enzyme defect, produces elevated urinary orotic acid from cytosolic carbamoyl phosphate overflow into pyrimidine synthesis.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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