Photoproduction of ammonium ion from N2 in Rhodospirillum rubrum.
NH+4 excretion was undetectable in N2-fixing cultures of Rhodospirillum rubrum (S-1) and nitrogenase activity in these cultures was repressed by the addition of 10 mM NH+4 to the medium. The glutamate analog, L-methionine-DL-sulfoximine (MSX), derepressed N2 fixation even in the presence of 10 mM extracellular NH+4. When 10 mg MSX/ml was added to cultures just prior to nitrogenase induction they developed nitrogenase activity (20% of the control activities) and excreted most of their fixed N2 as NH+4. Nitrogenase activities and NH+4 production from fixed N2 were increased considerably when a combined nitrogen source, NH+4 (greater than 40 mumoles NH+4/mg cell protein in 6 days) or L-glutamate (greater than 60 mumoles NH+4/ mg cell protein in 6 days) was added to the cultures together with MSX. Biochemical analysis revealed that R. rubrum produced glutamine synthetase and glutamate synthase (NADP-dependent) but no detectable NADP-dependent glutamate dehydrogenase. The specific activity of glutamine synthetase was observed to be maximal when nitrogenase activity was also maximal. Nitrogenase and glutamine synthetase activities were repressed by NH+4 as well as by glutamate. The results demonstrate that utilization of solar energy to photoproduce large quantities of NH+4 from N2 is possible with photosynthetic bacteria by interfering with their regulatory control of N2 fixation.
D005969:Glutamate Dehydrogenase / Q000032:analysis; D005970:Glutamate Synthase / Q000032:analysis; D005974:Glutamate-Ammonia Ligase / Q000032:analysis; D008717:Methionine Sulfoximine / Q000494:pharmacology; D009586:Nitrogen Fixation; D009591:Nitrogenase / Q000378:metabolism; D010788:Photosynthesis; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D012247:Rhodospirillum rubrum / Q000378:metabolism*
D000644:Quaternary Ammonium Compounds; D008717:Methionine Sulfoximine; D009591:Nitrogenase; D005970:Glutamate Synthase; D005969:Glutamate Dehydrogenase; D005974:Glutamate-Ammonia Ligase