Patterns of [13N]ammonium uptake and assimilation by Frankia HFPArl3 |
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Authors: | Alison M Berry James R Thayer Carol S Enderlin A Daniel Jones |
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Institution: | (1) Department of Environmental Horticulture, University of California, 95616 Davis, CA, USA;(2) Crocker Nuclear Laboratory, University of California, 95616 Davis, CA, USA;(3) Facility for Advanced Instrumentation, University of California, 95616 Davis, CA, USA |
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Abstract: | Nitrogen-starved cells of Frankia strain HFPArl3 incorporated 13N]-labeled ammonium into glutamine serine (glutamate, alanine, aspartate), after five-minute radioisotope exposures. High initial endogenous pools of glutamate were reduced, while total glutamine increased, during short term NH
inf4
sup+
incubation. Preincubation of cells in methionine sulfoximine (MSX) resulted in 13N]glutamine reduced by more than 80%, while 13N]glutamate and 13N]alanine levels increased. The results suggest that glutamine synthetase is the primary enzyme of ammonium assimilation, and that glutamate dehydrogenase and alanine dehydrogenase may also function in ammonium assimilation at low levels. Efflux of 13N]serine and lesser amounts of 13N]glutamine was detected from the Frankia cells. The identity of both Ser and Gln in the extracellular compartment was confirmed with gas chromatography/mass spectrometry. Serine efflux may be of significance in nitrogen transfer in Frankia.Abbreviations Pthr
phosphothreonine
- Aad
-amino-adipate
- MSX
methionine sulfoximine |
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Keywords: | Frankia Nitrogen fixation Glutamine synthetase Ammonium assimilation Serine |
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