Effect of nitrogen compounds on nitrogenase activity inAzospirillum brasilense

The effect of certain nitrogen compounds on nitrogenase activity was studied in cells of Azospirillum brasilense strain Sp6, grown under microaerophilic conditions with nitrogenase fully derepressed. 0.5 mM NH4Cl, 0.5 mM glutamine, 1.0 mM KNO3 and 0.1 mM KNO2 completely blocked nitrogenase activity. 1.0 mM asparagine, 1.0 mM aspartate, 1.0 mM histidine and 1.0 mM adenine did not caused no inhibition of nitrogenase; indeed asparagine, aspartate and histidine showed a slight stimulatory effect on N2 fixation. The addition of 10 mM dl-methionine-dl-sulphoximine prevented the inhibitory effect of NH4Cl and glutamine but did not counteract the effect of KNO2. Rifampicin and chloramphenicol did not prevent the inhibition of nitrogenase by NH4Cl.