Regulation of human carbamoyl phosphate synthetase II differs fundamentally from the bacterial enzyme aspartate transcarbamoylase. Which pattern is correct for mammalian CPS II?
- A Inhibited by UTP, activated by PRPP ✓
- B Inhibited by CTP, activated by ATP
- C Inhibited by arginine, activated by N-acetylglutamate
- D Inhibited by PRPP, activated by UTP
Correct answer: A. Inhibited by UTP, activated by PRPP
Explanation
Mammalian CPS II, located in the cytosol as part of the CAD complex, is inhibited by the pathway end product UTP and activated by PRPP, linking pyrimidine synthesis to purine availability. Option B describes the classic E. coli ATCase control system. Option C describes mitochondrial CPS I of the urea cycle, which requires N-acetylglutamate as an obligate activator. Confusing CPS I with CPS II is the single most tested error in this area.
Reference: Lippincott's Illustrated Reviews: Biochemistry, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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