The enzyme that links carbon and nitrogen metabolism is:
A. Glutamine synthetase.
B. Transketolase.
C. Glutamate dehydrogenase.
D. Enolase.

Uncovering the Enzyme That Connects Carbon and Nitrogen Metabolism

Introduction

In cellular metabolism, carbon and nitrogen are two fundamental elements that must be tightly coordinated. The link between carbon metabolism (like the TCA cycle) and nitrogen metabolism (like amino acid biosynthesis) is made by a single, crucial enzyme.

Question: Which enzyme connects carbon and nitrogen metabolism?

• A. Glutamine synthetase
• B. Transketolase
• C. Glutamate dehydrogenase
• D. Enolase

Let’s explore the answer and understand why it matters.

The Correct Answer: C. Glutamate Dehydrogenase

The enzyme glutamate dehydrogenase (GDH) plays a central role in bridging carbon and nitrogen metabolism.

What Does Glutamate Dehydrogenase Do?

GDH catalyzes the reversible reaction:

                 α-ketoglutarate  + NH4+    +NAD(P)H              ↔      glutamate+NAD(P)+

This means it:

• Takes a carbon intermediate from the TCA cycle (α-ketoglutarate)
• Combines it with ammonium (a nitrogen source)
• Produces glutamate, a key amino acid and nitrogen donor

Why Is This Important?

• Carbon metabolism produces energy and intermediates like α-ketoglutarate
• Nitrogen metabolism manages the synthesis and recycling of amino acids
• GDH acts as a metabolic hub, linking these two systems to maintain balance

Other Options Explained

• A. Glutamine synthetase: Important in nitrogen metabolism, but doesn’t directly link carbon cycle intermediates.
• B. Transketolase: Functions in the pentose phosphate pathway, a carbon pathway only.
• D. Enolase: Glycolytic enzyme, unrelated to nitrogen metabolism.

Conclusion

The enzyme glutamate dehydrogenase serves as the biochemical bridge between carbon and nitrogen metabolism. It connects the TCA cycle to amino acid biosynthesis and nitrogen assimilation, making it crucial for cellular homeostasis.

✅ Correct Answer: C. Glutamate dehydrogenase