Query (optional)   in Class  All Allele Author Colleague Collection Assembly Gene Gene Class Gene Product Germplasm Image Journal Keyword Library Locus Map Map Data Marker Pathology Polymorphism Probe Protein QTL Rearrangement Reference Sequence Species Trait Trait Study Two Point Data  

---

GrainGenes Reference Report: PPS-105-415

[Submit comment/correction]

Reference	PPS-105-415
Title	A metabolic control analysis of the glutamine synthetase/glutamate synthase cycle in isolated barley (Hordeum vulgare L.) chloroplasts
Journal	Plant Physiology
Year	1994
Volume	105
Pages	415-424
Author	Baron A Tobin T Wallsgrove R Tobin A
Abstract	Ammonia assimilation in chloroplasts occurs via the glutamine synthetase/glutamate synthase (GS/GOGAT) cycle To determine the extent to which these enzymes contribute to the control of ammonia assimilation, a metabolic control analysis was performed on isolated barley (Hordeum vulgare L.) leaf chloroplasts Pathway flux was measured polarographically as ammonium-plus-2-oxoglutarate-plus-glutamine-dependent evolution in illuminated chloroplasts Enzyme activity was modulated by titration with specific, irreversible inhibitors of GS (phosphinothricin) and GOGAT (azaserine) Flux control coefficients were determined (a) by differentiation of best-fit hyperbolic curves of the data sets flux versus enzyme activity), and (b) from estimates of the deviation indices (deviation index). Both analyses gave similar values for the coefficients. The control coefficient for GS was relatively high and the value did not change significantly with changes in 2-oxoglutarate concentration (flux control coefficient = 0.58 at 5 millimole 2-oxoglutarate and 0.40 at 20 millimole 2-oxoglutarate). The control coefficient for GOGAT decreased with decreasing glutamine concentrations, from 0.76 at 20 millimole glutamine to 0.19 at 10 millimole glutamine. Thus, at high concentrations of glutamine, GOGAT exerts a major control over flux with a significant contribution also from GS. At lower concentrations of glutamine, however, GOGAT exerts far less control over pathway flux.
Keyword	[ Hide all but 1 of 11 ] biochemical-pathways chemical-reactions chloroplasts enzyme activity equations glutamate-ammonia-ligase glutamate-synthase hordeum vulgare leaves metabolism regulation

GrainGenes is a product of the Agricultural Research Service of the US Department of Agriculture.