Effect of carbon monoxide on biological nitrogen fixation: What happens to nitrogenase activity in the presence of CO?

Introduction / Context:
Nitrogenase catalyzes the ATP-dependent reduction of atmospheric nitrogen (N2) to ammonia (NH3). Certain gases interfere with the enzyme’s metal centers. Understanding inhibitors helps interpret ecological and laboratory observations.

Given Data / Assumptions:

• Nitrogenase contains complex metal cofactors (Fe protein and MoFe protein).
• Carbon monoxide (CO) is known to bind to metal centers.
• Question asks for the qualitative effect of CO on nitrogen fixation.

Concept / Approach:
CO binds at or near catalytic metal clusters, blocking electron transfer and inactivating nitrogenase. Therefore, the enzyme cannot reduce N2 to NH3 when exposed to CO.

Step-by-Step Solution:

Verification / Alternative check:
Classic biochemical studies show rapid loss of nitrogenase activity upon CO exposure; removal of CO restores activity if no irreversible damage occurred.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing O2 sensitivity (which also inactivates nitrogenase) with CO inhibition; both impair the enzyme but by different mechanisms.

Final Answer:
Nitrogen fixation is inhibited (CO acts as a specific inhibitor).