Purification of azotophore membranes containing the nitrogenase from Azotobacter vinelandii

Azotophore membranes containing nitrogenase have been purified in high yield from $\text{A. vinelandii}$ by differential and sucrose density gradient sedimentation. The purified preparations appeared as uniform vesicular membranes of 40–75 nm diameter containing the majority of the nitrogenase activity from these cells and were readily separated from the intracytoplasmic membranes containing the cytochromes of the respiratory electron transfer system. The yield and specific activity of azotophores from cells broken by mechanical or osmotic treatment were similar.