Question

Which factors do show considerable influence on the activity of nitrogenase enzyme during $N_{2}$ fixation?
A. Molybdenum
B. Molecular $H_{2}$
C. Boron
D. Leghemoglobin
Choose the correct answer from the options given below:

• A. A, C and D only
• B. B, C and D only
• C. C, B and A only
• D. D, A and B only

Hint:

To remember Nitrogenase factors: Mo (Metal core), $H_2$ (The byproduct), and Leghemoglobin (The oxygen shield).

Answer 1

The Correct Option is D

Concept: The nitrogenase enzyme complex is the biological engine of nitrogen fixation. Its activity is governed by specific chemical components, environmental conditions, and protective proteins.

Step 1: The Structural Factor: Molybdenum (A).
Nitrogenase is a metalloenzyme. The active site of the larger protein component (the dinitrogenase) contains a unique Molybdenum-Iron (MoFe) cofactor. Without Molybdenum, the enzyme cannot catalyze the reduction of $N_2$ to $NH_3$.

Step 2: The Kinetic Factor: Molecular $H_2$ (B).
During the reduction process, nitrogenase inevitably produces $H_2$ gas. This is a competitive process; high levels of molecular $H_2$ can actually inhibit the enzyme's efficiency by acting as a product inhibitor or diverting reducing power away from nitrogen fixation.

Step 3: The Protective Factor: Leghemoglobin (D).
Nitrogenase is irreversibly poisoned by oxygen. In root nodules, Leghemoglobin acts as an oxygen scavenger, maintaining an extremely low oxygen tension (anaerobic environment) to protect the enzyme while still providing enough oxygen for the bacteria's respiration.

Step 4: Conclusion.
While Boron (C) is a plant micronutrient, it is not a direct co-factor or regulator of the nitrogenase enzyme's catalytic activity in the same way that A, B, and D are. Therefore, option (4) is the correct choice.