A Report On Another Degradation Enzyme Is Glutamine Synthetase

After astrocytes remove glutamate from the ECS, glutamate must be isolated and degraded. Glutamate transporters are bidirectional, so intracellular elevations of glutamate levels will lead to an electrochemical gradient-mediated release if the molecule is not destroyed. If glutamate release is unregulated glutamate accumulates in the ECS and impairs the survival of neurons. Glutamate dehydrogenase (GDH) helps degrade glutamate into a-ketoglutarate, an intermediary in the tricarboxylic acid (TCA) cycle (Coulter and Steinhauser, 2015). Superfluous glutamate release depletes the TCA cycle of intermediates and impairs ATP synthesis (Coulter and Eid, 2012). Another degradation enzyme is glutamine synthetase (GS), found predominantly in astrocytes and catalyzes the conversion of glutamate into glutamine (Coulter and Steinhauser, 2015). Glutamine leaves astrocytes via the N transporter 1 system and is transferred to presynaptic terminals via the A type glutamine transporter SAT1 to be recycled back into glutamate. Healthy glial cells express abundant GDH and GS, but tissue sample from patients with MTLE-HS have shown a pronounced deficit in both enzymes. The downregulation of GS is particularly evident in hippocampal samples with astrogliosis. GS deficiency slows the cycling of glutamate to glutamine and impacts the synapse by elevating astroglial and extracellular concentrations of glutamate while decreasing the synthesis of GABA (Coulter and Eid, 2012).
Glutamine is transported…