N-acetylglutamate (NAG) is an essential allosteric activator of carbamoyl phosphate synthetase-I (CPS-I), the first committed step of the urea cycle. Which amino acid's catabolism generates acetyl-CoA that is used by NAG synthase to produce NAG?

• A Glutamine
• B Arginine
• C Alanine
• D Glutamate, which directly provides both the acetyl (from acetyl-CoA) and glutamate moieties for NAG synthesis ✓

Explanation

N-acetylglutamate synthase (NAGS) catalyzes the condensation of acetyl-CoA and glutamate to produce N-acetylglutamate (NAG). Arginine allosterically activates NAGS, creating a positive feedback loop: as amino acid catabolism increases, arginine (the direct precursor of urea) rises and stimulates NAG production, which then activates CPS-I to increase urea cycle flux. Inherited NAGS deficiency is a rare urea cycle disorder that responds to N-carbamylglutamate (carglumic acid) treatment, which mimics NAG and directly activates CPS-I.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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