Question

An intermediate of TCA cycle found in the reaction of Urea cycle is

• A. Succinate
• B. Succinyl CoA
• C. Fumarate
• D. Arginine

Hint:

Krebs Bicycle Linkage: Fumarate is produced by Argininosuccinate Lyase in the Urea Cycle and directly integrates into the TCA Cycle.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The 'Krebs Bicycle' (Aspartate-Argininosuccinate Shunt) metabolically interconnects the cytoplasmic Urea Cycle with the mitochondrial TCA Cycle.
Key Formula or Approach:
\[ \text{Argininosuccinate} \xrightarrow{\text{Argininosuccinase (Argininosuccinate Lyase)}} \text{L-Arginine} + \text{Fumarate (Enters TCA Cycle)} \]

Step 2: Detailed Explanation:
In nitrogen metabolism and the Krebs bicycle:
- In Step 4 of the Urea Cycle, cytosolic argininosuccinate lyase cleaves argininosuccinate into L-Arginine (which continues in the urea cycle to form urea and ornithine) and Fumarate.
- Fumarate is hydrated to malate by cytosolic fumarase, transported into the mitochondrial matrix via the malate-aspartate shuttle, and enters the TCA Cycle to yield oxaloacetate, which is transaminated back into aspartate to feed the next round of the urea cycle.

Step 3: Final Answer:
Therefore, the intermediate found in both cycles is Fumarate, corresponding to option (C).