{"type":"root","children":[{"type":"paragraph","children":[{"type":"text","value":"Glutamine synthetase (GS) is an ATP dependent enzyme that plays an essential role in the metabolism of nitrogen by catalyzing the condensation of glutamate and ammonia to form glutamine. GS is present predominantly in the brain, kidneys, and liver. In the brain, GS is predominantly expressed in astrocytes, where it participates in the astrocytic-neuronal glutamate-glutamine cycle, helping to maintain low levels of extracellular glutamate and prevent excitotoxicity. In the liver, GS is expressed in hepatocytes and plays a role in the detoxification of ammonia generated from amino acid metabolism. Aberrant GS expression or activity in the liver may be associated with hepatic dysfunction and metabolic disorders, including hepatic encephalopathy and liver cirrhosis. Loss of GS expression or aberrant cytoplasmic localization may be observed in hepatocellular carcinoma (HCC) and confirm the hepatic origin of tumor. Glutamine metabolism, including GS activity, is often dysregulated in cancer cells, leading to increased glutamine consumption and dependence on glutamine for proliferation and survival. Therefore, high levels of GS expression or activity may be observed in certain types of cancer characterized by glutamine addiction, such as glioblastoma, melanoma, and certain subtypes of breast cancer."}]}]}