117. Which one of the following is a Mo-Fe containing protein?
(1) Nitrate reductase
(2) Nitrogenase
(3) Nitrite reductase
(4) Leghemoglobin

Detailed Explanation:

Question:
Which one of the following is a Mo-Fe containing protein?

✅ Correct Answer: (2) Nitrogenase

What is a Mo-Fe Protein?

Mo-Fe proteins contain molybdenum (Mo) and iron (Fe) cofactors that are crucial for their enzymatic activity. These cofactors often participate in redox reactions, especially those involved in nitrogen metabolism in plants and microorganisms.

Nitrogenase – The Mo-Fe Protein

Nitrogenase is an enzyme complex that plays a critical role in biological nitrogen fixation, converting atmospheric nitrogen (N₂) into ammonia (NH₃), which plants can use.

🔬 Key Features of Nitrogenase:

• Composed of two main protein components:

  • Fe protein (iron-containing)

  • MoFe protein (molybdenum-iron containing)

• The MoFe cofactor (FeMo-co) is where nitrogen reduction occurs.

• Functions under anaerobic conditions, as oxygen can inactivate it.

• Requires ATP and electrons to drive the conversion of N₂ to NH₃.

Why Nitrogenase is the Correct Answer:

Among the listed options:

• (1) Nitrate reductase – contains Mo, but not Fe-Mo cofactor as in nitrogenase.

• (2) Nitrogenase – contains the MoFe cofactor, making it a true Mo-Fe protein.

• (3) Nitrite reductase – does not contain MoFe; often contains siroheme or Fe-S clusters.

• (4) Leghemoglobin – is an iron-containing heme protein, but does not contain molybdenum.

Biological Importance of Nitrogenase:

• Found in diazotrophs (nitrogen-fixing bacteria), including Rhizobium species in legume root nodules.

• Crucial for agriculture and ecosystem nitrogen cycles.

• Works in symbiosis with legumes to enrich the soil with usable nitrogen.

Conclusion:

The MoFe-containing protein among the listed options is clearly Nitrogenase, which plays a vital role in nitrogen fixation and is central to soil fertility and plant growth.

✅ Correct Answer: (2) Nitrogenase