Kinetic commitment in the catalysis of glutamine synthesis by GS1 from Arabidopsis using 14N/15N and solvent isotope effects
Copyright © 2016 Elsevier Masson SAS. All rights reserved.
| Veröffentlicht in: | Plant physiology and biochemistry : PPB. - 1991. - 108(2016) vom: 22. Nov., Seite 203-211 |
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| 1. Verfasser: | |
| Weitere Verfasser: | , , , , |
| Format: | Online-Aufsatz |
| Sprache: | English |
| Veröffentlicht: |
2016
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| Zugriff auf das übergeordnete Werk: | Plant physiology and biochemistry : PPB |
| Schlagworte: | Journal Article Amidation Catalysis Glutamine Isotope effect Kinetic commitment Arabidopsis Proteins Carbon Isotopes Nitrogen Isotopes Solvents mehr... |
| Zusammenfassung: | Copyright © 2016 Elsevier Masson SAS. All rights reserved. Glutamine synthetase (GS, EC 6.3.1.2) catalyzes the production of glutamine from glutamate, ammonium and ATP. Although being essential in plants for N assimilation and recycling, kinetic commitments and transition states of the reaction have not been clearly established yet. Here, we examined 12C/13C, 14N/15N and H2O/D2O isotope effects in Arabidopsis GS1 catalysis and compared to the prokaryotic (Escherichia coli) enzyme. A14N/15N isotope effect (15V/K ≈ 1.015, with respect to substrate NH4+) was observed in the prokaryotic enzyme, indicating that ammonium utilization (deprotonation and/or amidation) was partially rate-limiting. In the plant enzyme, the isotope effect was inverse (15V/K = 0.965), suggesting that the reaction intermediate is involved in an amidation-deamidation equilibrium favoring 15N. There was no 12C/13C kinetic isotope effect (13V/K = 1.000), suggesting that the amidation step of the catalytic cycle involves a transition state with minimal alteration of overall force constants at the C-5 carbon. Surprisingly, the solvent isotope effect was found to be inverse, that is, with a higher turn-over rate in heavy water (DV ≈ 0.5), showing that restructuration of the active site due to displacement of H2O by D2O facilitates the processing of intermediates |
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| Beschreibung: | Date Completed 07.04.2017 Date Revised 30.09.2020 published: Print-Electronic Citation Status MEDLINE |
| ISSN: | 1873-2690 |
| DOI: | 10.1016/j.plaphy.2016.07.015 |