Question

The nitrogenase of diazotrophs

• A. contains Cu-S center and uses 12 NADH to reduce one N$_2$
• B. contains one (4Fe–4S) cluster and uses 8 FADH$_2$ to reduce one N$_2$
• C. is a complex of Fe-protein and MoFe-protein and uses 16 ATPs to reduce one N$_2$
• D. is a MoFe protein and uses 4 ATP and 4 FMNH$_2$ to reduce one N$_2$

Hint:

Remember: Biological nitrogen fixation always requires 16 ATP per N$_2$ molecule reduced.

Answer 1

The Correct Option is C

Step 1: Understanding nitrogenase.
Nitrogenase is the enzyme complex responsible for biological nitrogen fixation in diazotrophic organisms. It consists of two components: Fe-protein (dinitrogenase reductase) and MoFe-protein (dinitrogenase).
Step 2: Energy requirement.
The reduction of atmospheric N$_2$ to ammonia (NH$_3$) is highly energy-intensive and requires 16 ATP molecules per N$_2$ reduced.
Step 3: Evaluating options.
(A) Incorrect — nitrogenase does not contain Cu-S centers.
(B) Incorrect — the (4Fe–4S) cluster is present but not the correct ATP/FADH$_2$ usage.
(C) Correct — Fe-protein + MoFe-protein complex and 16 ATP per N$_2$.
(D) Incorrect — wrong cofactor and ATP requirement.
Step 4: Conclusion.
Thus, option (C) correctly describes nitrogenase.