Beyond its primary role in reducing atmospheric nitrogen to ammonia during symbiotic nitrogen fixation, the nitrogenase enzyme complex is also capable of catalyzing other reactions. Listed below are some reactions:
A. Acetylene reduction (C₂H₂ → C₂H₄)
B. H₂ production (2H⁺ → H₂)
C. ATP hydrolysis (ATP → ADP + Pi)
D. Oxidized ferredoxin to reduced ferredoxin
E. NAD reduction (NAD⁺ + H⁺ → NADH)
Which one of the following options represents the combination of reactions that are NOT catalysed by the nitrogenase enzyme complex?

Correct option is B

Correct Answer:
(b) D and E
Explanation:
Nitrogenase can catalyze acetylene reduction (used experimentally to assay nitrogenase activity) and also produces molecular hydrogen (H₂) as a side reaction. ATP hydrolysis occurs within the nitrogenase complex to provide energy for electron transfer.
However, reduction of ferredoxin is carried out by other cellular enzymes upstream of nitrogenase, and NAD⁺ reduction to NADH is not a reaction catalyzed by nitrogenase.
Information Booster:
· Nitrogenase is a multi-component enzyme requiring ATP and low-potential electrons.
· Acetylene reduction is a standard proxy for nitrogenase activity.
· Hydrogen evolution is an obligate side reaction of nitrogen fixation.
· Electron donors like ferredoxin are reduced outside the nitrogenase complex.
Additional Information (Incorrect Options):
Option (a): Incorrect because both hydrogen production and ATP hydrolysis are part of nitrogenase function.
Option (c): Incorrect since acetylene reduction is a hallmark nitrogenase reaction.
Option (d): Incorrect because hydrogen production is catalysed by nitrogenase.