In the urea cycle, fumarate is produced as a byproduct. This fumarate connects the urea cycle to the TCA cycle. Which urea cycle enzyme generates fumarate?
- A Argininosuccinate synthetase
- B Argininosuccinate lyase ✓
- C Arginase
- D Ornithine transcarbamylase
Correct answer: B. Argininosuccinate lyase
Explanation
Argininosuccinate lyase cleaves argininosuccinate into arginine and fumarate. This fumarate can enter the TCA cycle (the 'Krebs bicycle' linking urea and TCA cycles). Argininosuccinate synthetase consumes ATP to form argininosuccinate. Arginase releases urea from arginine. OTC catalyzes the condensation of carbamoyl phosphate with ornithine.
Reference: Lehninger Principles of Biochemistry, 8th ed.
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