Which enzyme mediates the reduction of nitrate to nitric oxide in bacteria?

Which enzyme mediates the reduction of nitrate to nitric oxide in bacteria?

• A. Nitrate reductase
• B. Nitrite reductase
• C. Ammonia monooxygenase
• D. Urease

Answer: (A)

In bacteria that perform denitrification, nitrate is reduced stepwise to nitrite and then to nitric oxide. The first step, reducing nitrate (NO3−) to nitrite (NO2−), is carried out by nitrate reductase. The next step, converting nitrite to nitric oxide (NO), is done by nitrite reductase. So, when focusing on the reduction of nitrate toward nitric oxide, the enzyme that directly mediates the initial reduction is nitrate reductase, initiating the pathway toward NO production. The other enzymes listed don’t perform this nitrate-to-nitrite step: ammonia monooxygenase is involved in ammonia oxidation, and urease breaks down urea into ammonia, not part of this denitrification sequence.

In bacteria that perform denitrification, nitrate is reduced stepwise to nitrite and then to nitric oxide. The first step, reducing nitrate (NO3−) to nitrite (NO2−), is carried out by nitrate reductase. The next step, converting nitrite to nitric oxide (NO), is done by nitrite reductase. So, when focusing on the reduction of nitrate toward nitric oxide, the enzyme that directly mediates the initial reduction is nitrate reductase, initiating the pathway toward NO production. The other enzymes listed don’t perform this nitrate-to-nitrite step: ammonia monooxygenase is involved in ammonia oxidation, and urease breaks down urea into ammonia, not part of this denitrification sequence.