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If a Azotobacter is free living nitrogen fixer it will also require ATP through cellular respiration. I am confused here: if Nitrogenase is highly sensitive to oxygen molecule how will Azotobacter be able to fix N2 and carry out cellular respiration at the same time?

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https://en.wikipedia.org/wiki/Azotobacter#Nitrogen_fixation

Nitrogen fixation is highly sensitive to the presence of oxygen, so Azotobacter developed a special defensive mechanism against oxygen, namely a significant intensification of metabolism that reduces the concentration of oxygen in the cells.[40]

From that cite "Respiratory Protection nitrogenase complex in Azotobacter vinelandii"(google translated)

The second strategy, dubbed "breath protection ", is based on a significant increase in the rate of the rate of respiration, resulting in the concentration of oxygen in the cytoplasm decreases to a level at which nitrogenase no longer experiences damaging action О2 .

https://en.wikipedia.org/wiki/Azotobacter#Nitrogen_fixation

Also, a special nitrogenase-protective protein protects nitrogenase and is involved in protecting the cells from oxygen. Mutants not producing this protein are killed by oxygen during nitrogen fixation in the absence of a nitrogen source in the medium.[41]

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