Nitrogen fixation in extracts of Azotobacter vinelandii

When cells of Azotobacter vinelandii (O) strain grown for 18 h. at 30° were disrupted in the culture medium in which they were grown, either by lysozyme treatment or by the ultrasonic probe, they incorporated nitrogen‐15 in amounts that were comparable to those assimilated by whole cells. Even cell‐free extracts prepared by centrifuging the treated cells in the culture medium at 25,000 g for 30 min., showed a significant enrichment of the stable isotope, viz., between 0‐22 and 0‐54 atom‐% excess, which is more than 100 times the values recorded previously. This probably constitutes the first unequivocal demonstration of nitrogen fixation in cell‐free extracts of a nitrogen‐fixing organism.