Glutamine synthetase of Chlamydomonas: its role in the control of nitrate assimilation |
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Authors: | Julie V. Cullimore Anthony P. Sims |
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Affiliation: | (1) School of Biological Sciences, University of East Anglia, NR4 7TJ Norwich, UK;(2) Present address: Biochemistry Department, Rothmsted Experimental Station, AL5 2JQ Harpenden, Herts, UK |
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Abstract: | Work is described which suggests that glutamine synthetase (GS) could play an important and direct regulatory role in the control of NO3 assimilation by the alga. In both steady-state cells and ones disturbed physiologically by changes in light or nitrogen supply the assimilation of NO3 appears to be limited by the activity of GS. Moreover although in normal cells NH3 can completely inhibit NO3 uptake, promote the deactivation of nitrate reductase (NR) and repress the synthesis of NR and nitrite reductase (NIR), these controls are relaxed in cells in which GS is deactivated by treatment with L-methionine-DL-sulfoximine (MSO). It is proposed that the reversible deactivation of GS may play an important part in the regulation of NO3 assimilation although it is still not clear whether the enzyme itself or products of its metabolism are responsible.Abbreviations GS glutamine synthetase - GSs glutamine synthetase, synthetase activity - GSt glutamine synthetase, transferase activity - NR nitrate reductase - NIR nitrite reductase - GDH glutamate dehydrogenase - CHX cycloheximide - MSO L-methionine-DL-sulfoximine - FAD flavine adenine dinucleotide |
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Keywords: | Chlamydomonas Glutamine synthetase Nitrate assimilation (regulation) Nitrale reductase |
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