Question

Which enzyme catalyzes the conversation of molecular $N_{2}$ to $NH_{3}$?

• A. Dehydrogenase
• B. Nitrogenase
• C. Oxygenase
• D. Desaturase

Hint:

Nitrogenase is the "Star" of the show. No other enzyme in nature can turn air into fertilizer!

Answer 1

The Correct Option is B

Concept: The conversion of atmospheric dinitrogen ($N_2$) into ammonia ($NH_3$) is the foundation of biological nitrogen fixation. This process is exclusively performed by certain prokaryotes.

Step 1: The Role of Nitrogenase.
The Nitrogenase enzyme complex is the only biological catalyst capable of breaking the exceptionally strong triple bond ($N \equiv N$) of atmospheric nitrogen. It consists of two protein components: the Fe-protein (reductase) and the MoFe-protein (dinitrogenase).

Step 2: Oxygen Sensitivity.
A unique feature of Nitrogenase is that it is highly sensitive to oxygen ($O_2$), which irreversibly inactivates it. Therefore, diazotrophs have evolved various strategies (like heterocysts in Nostoc or leghemoglobin in nodules) to protect the enzyme during catalysis.

Step 3: Eliminating Others.
Dehydrogenases (1) remove hydrogen. Oxygenases (3) add oxygen. Desaturases (4) create double bonds in fatty acids. None of these are involved in fixing nitrogen.