title: Molybdenum independence of nitrogenase component synthesis in the non-heterocystous cyanobacterium Plectonema.
abstract: The cyanobacterium Plectonema boryanum (IU 594-UTEX 594) fixes N2 only in the absence of combined N and of O2. We induced nitrogenase by transfer to anaerobic N-free medium and studied the effect of Mo starvation on nitrogenase activity and synthesis. Activity was first detected within 3 h after transfer by the acetylene reduction assay in controls, increasing for at least 25 h. Cells grown on nitrate and Mo and then transferred to N-free, Mo-free medium produced 8% of the control nitrogenase activity. Addition of W to the Mo-free medium reduced the activity to 0.5%. Under both Mo starvation conditions, nitrogenase protein components were synthesized. Component II of the cyanobacterial enzyme was detected by in vitro complementation with Mo-containing component I from Klebsiella pneumoniae or Azotobacter vinelandii but not Clostridium pasteurianum. Component I activity was restored by addition of Mo to cultures in which new enzyme synthesis was blocked by chloramphenicol. Acidified extracts of Plectonema induced in Mo-containing medium contained the Fe-Mo cofactor required to activate extracts of the Azotobacter mutant UW45 in vitro, but they did not activate extracts of Mo-starved Plectonema. Analysis of 35SO4(2-)-labeled proteins by polyacrylamide gel electrophoresis suggested that Mo is required for the conversion of a high-molecular-weight precursor to component I in Plectonema.
mesh_terms: D000641:Ammonia / Q000494:pharmacology; D000458:Cyanobacteria / Q000201:enzymology*; D004789:Enzyme Activation; D004790:Enzyme Induction; D008717:Methionine Sulfoximine / Q000494:pharmacology; D008982:Molybdenum / Q000494:pharmacology*; D009566:Nitrates / Q000494:pharmacology; D009591:Nitrogenase / Q000096:biosynthesis* / Q000378:metabolism; D010100:Oxygen / Q000494:pharmacology; D010940:Plant Proteins / Q000096:biosynthesis
chemical_list: D009566:Nitrates; D010940:Plant Proteins; D008717:Methionine Sulfoximine; D000641:Ammonia; D008982:Molybdenum; D009591:Nitrogenase; D010100:Oxygen