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Description

Glutamine synthetase (EC 4.1.1.15, EC 6.3.1.2, UniProt P09606, also known as Glutamate-ammonia ligase, Glutamate decarboxylase, GS) is encoded by the Glul (also known as Glns) gene (Gene ID 24957) in rat species. Glutamine synthetase (GS) plays an essential role in nitrogen metabolism by catalyzing ATP-dependent condensation of glutamate and ammonia to form glutamine. Three classes of GS exist, class I enzymes (GSI) are specific to prokaryotes and exist as oligomers of 12 identical subunits, class II enzymes (GSII) exist as decamer of identical subunits in eukaryotes and in some bacteria, while class III enzymes (GSIII) function as a double-ringed dodecamer of identical chains found in bacteroides fragilis and in butyrivibrio fibrisolvens. GS is present predominantly in the brain, kidneys, and liver in mammals. In the brain, GS is found primarily in astrocytes, where it participates in the the detoxification of ammonia via assimilation and termination of neurotransmitter signals via recyclization. c-Myc promotes glutamine usage by upregulating glutaminase (GLS), which converts glutamine to glutamate in the TCA cycle, while in some cancer cells Myc-mediated thymine DNA glycosylase (TDG) transcription leads to GS upregulation due to TDG-dependent demethylation of the GS promoter. GS upregulation promotes cancer cell survival under glutamine limitation, while GS silencing decreases cancer cell proliferation and xenograft tumor growth.