33 by: Nicole Leighton
Student: Nicole Leighton
Enzyme Name: Glutamine Synthetase
Enzyme E.C Number: 6.3.1.2
Where is the enzyme found? Glutamine synthetase can be found in the brain, liver, muscle, adipose tissue and lungs (Castegna, A., 2018). As a specific example, in the glutamate-glutamine cycle, glutamine synthetase can be found in the brain in the astrocyte. (Andersen, J. V, 2021)
What does the enzyme do? In general, glutamine synthetase catalyses the reaction between glutamate and an ammonia ion to synthesise glutamine. It is ATP-dependent and it uses ions such as Mg2+ as cofactors during the reaction. A specific example of what this enzyme does can be found when observing the glutamine-glutamate cycle. Glutamine plays a role as one of the enzymes in the glutamate-glutamine cycle, which is a cycle that occurs in the brain. The glutamate-glutamine cycle starts in the pre synapse, where glutamine is converted to glutamate by the enzyme glutaminase. The synthesised glutamate is then packaged in vesicles for transport, but excess glutamate may build up in the synaptic cleft, in which case it can be uptaken by the astrocyte via transporters. In the astrocyte, the excess glutamate is converted back to glutamine by glutamine synthetase. The synthesised glutamine will travel from the astrocyte back to the pre synapse, where the cycle starts again. In short, glutamine synthetase converts glutamate to glutamine in the glutamate-glutamine cycle and thus helps regulate the amount of glutamate in the synaptic cleft. (Andersen, J. V, 2021)
Interesting facts about the enzyme – One interesting fact about glutamine synthetase is that it can be used for the early detection of tuberculosis. The bacteria that causes the disease, Mycobacterium tuberculosis, requires the synthesis of glutamate-glutamine chains for its cell wall. So, the enzyme is present in the early stages of the disease. (Group, T. (n.d.).)
References
Andersen, J. V., Markussen, K. H., Jakobsen, E., Schousboe, A., Waagepetersen, H. S., Rosenberg, P. A., & Aldana, B. I. (2021). Glutamate metabolism and recycling at the excitatory synapse in health and neurodegeneration. Neuropharmacology, 196, 108719. https://doi.org/10.1016/j.neuropharm.2021.108719
Castegna, A., & Menga, A. (2018). Glutamine synthetase: Localization dictates outcome. Genes, 9(2), 108. https://doi.org/10.3390/genes9020108
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Group, T. (n.d.). Mechanism and catalytic site Atlas. M-CSA Mechanism and Catalytic Site Atlas. https://www.ebi.ac.uk/thornton-srv/m-csa/entry/537/
