title: Repression, derepression and activation of nitrogenase in Azotobacter vinelandii.
abstract: Ammonium ion repressed nitrogenase in cells fixing N2 gas. Immunological tests and electrophoresis in various gels show that components I (Fe-Mo-S protein) was completely repressed by ammonium, whereas component II (Fe-S protein) apoprotein was not markedly affected. Component II from ammonium-grown cells, however, was inactive since it did not cross react with component I to reduce C2H2 to C2H4. The inactive component II apoprotein is immunologically identical to its active counterpart from cells fixing N2. Identical protein patterns were also observed in various gel-electrophoresis systems. Oxygen-inactivated component II may be reactivated with FeSo4. This salt is preferable to ferrous ammonium sulphate which inactivated component I. Immunodiffusion under aerobic conditions shows that purified component I is composed of aggregated and non-aggregated forms which are antigenically distinct. The aggregate was dissociated by treatment with sodium dodecyl sulphate (SDS) into a single antigenic species which was further resolved into two subunits on SDS disc polyacrylamide gel electrophoresis.
mesh_terms: D000643:Ammonium Chloride; D001395:Azotobacter / Q000201:enzymology*; D004789:Enzyme Activation; D004794:Enzyme Repression; D007501:Iron; D007527:Isoenzymes / Q000302:isolation & purification; D009591:Nitrogenase / Q000302:isolation & purification
chemical_list: D007527:Isoenzymes; D000643:Ammonium Chloride; D007501:Iron; D009591:Nitrogenase