Stability and ferrous iron content of the nitrogenase and its components from Azotobacter vinelandii

Summary Nitrogenase of Azotobacter vinelandii is sensitive to oxygen, and sensitivity develops during purification. Such inactivation is well prevented by 0.1% hydroquinone plus 0.01% ascorbate, which are also effective in preventing inactivation of enzyme on storage under H₂. Activity is proportional to ferrous iron content of crude sample of enzyme. On storage at 0°C, 0.3 M KCl inactivates the enzyme, while KCl stabilizes its components. Nitrogenase is not cold labile, while the components are cold labile; Fe, Mo-component is most stable at 22°C and Fe-component at 13.5°C. Nitrogenase substrates, except N₂, stabilize nitrogenase, but not the components.