Glutamate-glutamine cycle
- Glutamate-glutamine cycle
In biochemistry, the glutamate-glutamine cycle is a sequence of events by which an adequate supply of the neurotransmitter glutamate is maintained in the central nervous system.[cite book | author = Purves, Dale, George J. Augustine, David Fitzpatrick, William C. Hall, Anthony-Samuel LaMantia, James O. McNamara, and Leonard E. White | title = Neuroscience. 4th ed. | publisher = Sinauer Associates | pages = 128-9 | year = 2008 | id = ISBN 978-0-87893-697-7] ]Initially, glial cells release glutamine, which is then taken up into presynaptic terminals and metabolized into glutamate by glutaminase (a mitochondrial enzyme). Glutamate can also be produced by transamination of 2-oxoglutarate, an intermediate in the Citric acid cycle.
The glutamate that is synthesized in the presynaptic terminal is packaged into synaptic vesicles by the transporter VGLUT. Once the vesicle is released, glutamate is removed from the synaptic cleft by excitatory amino acid transporters (EAATs), of which there are five types. Glutamate taken up by glial cells is then converted into glutamine by glutamine synthetase, and transported out of the cells into the nerve terminal. This allows synaptic terminals and glial cells to work together in order to maintain a proper supply of glutamate.
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