Photoproduction of ammonium ion from N2 inRhodospirillum rubrum |
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Authors: | N M Weare K T Shanmugam |
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Institution: | (1) Department of Chemistry, University of California, San Diego, 92037 La Jolla, California, USA;(2) Plant Growth Laboratory/Department of Agronomy and Range Science, University of California, 95616 Davis, California, USA |
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Abstract: | NH
4
+
excretion was undetectable in N2-fixing cultures ofRhodospirillum 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
+
(>40 moles NH
4
+
/mg cell protein in 6 days) orl-glutamate (>60 moles NH
4
+
/mg cell protein in 6 days) was added to the cultures together with MSX.Biochemical analysis revealed thatR. 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. |
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Keywords: | Nitrogen fixation NH
4
+ excretion Photosynthesis Rhodospirillum rubrum Photosynthetic bacteria Enzymes of ammonia assimilation |
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