FIGURE 8-7 Steps involved in the synthesis and release of glutamate.
Regulation of glutamine synthetase in Streptomyces coelicolor.
GS is a highly controlled enzyme, subject to multiple forms of regulation (, ). A cascade of regulatory proteins and small molecule effectors, primarily glutamine and 2-oxoglutarate, control synthesis of GS. Each GS monomer in the 12-member holoenzyme is subject to rapid adenylylation and deadenylylation in response to the same effectors. The adenylylated form is much less active. Partial adenylylation of the holoenzyme sensitizes it to feedback inhibition by a variety of small molecules that may be construed as end products of GS activity.
Glutamate in plants: metabolism, regulation, and signalling.
The relative importance of each of the two glutamate pathways during glucose-limited growth varies (in opposite directions) as a function of phosphate and ammonium concentrations (). However, the levels of two of the three relevant enzymes, GDH and GOGAT, remain low during glucose-limited growth in continuous culture and do not change markedly with change in ammonium or phosphate level under conditions in which pathway choice appears to be controlled by these compounds (). In the work described in this report, I looked at the level and form (adenylylated or unadenylylated) of the third enzyme, glutamine synthetase, to see if either varied with conditions controlling choice of pathway for glutamate synthesis. The results show that regulation of the form or amount of GS is also insufficient to control the choice of pathway. Thus, concentration of substrates and/or modulation of enzyme activity is likely to be a major determinant of pathway choice in glutamate synthesis.
Effect of glucose on aspartate and glutamate synthesis …
4. Glutamine is transported out of the glia into the neuro-nal terminal via glutamine transporters located in the glial and neuronal terminal membranes.
Start studying Neurotransmitters 1: Glutamate, GABA, Acetylcholine
The present study was conducted to study this metabolic interaction in cultured GABAergic neurons exposed to different combinations of (13)C-labeled and unlabeled glucose and ß-hydroxybutyrate.