GLS (Glutaminase) is the K-type mitochondrial glutaminase, a phosphate-activated amidohydrolase that catalyzes the hydrolysis of glutamine to glutamate and ammonia. This protein is primarily expressed in axonal terminals of neurons in the brain and in periportal hepatocytes and renal tubules in the kidney. It plays a pivotal role in generating energy for metabolism, synthesizing the brain neurotransmitter glutamate and in maintaining acid-base balance in the kidney. As numerous cancers use glutamate for metabolic and proliferative processes, GLS inhibitors are of interest as potential cancer treatments. In immunohistochemistry, GLS has highest granular cytoplasmic positivity in the brain and kidney, and is also found in the thyroid, lung, gastrointestinal tract, liver, pancreas, reproductive tissues and muscle. References: International Journal of Molecular Sciences. 16 (9): 22830–55, PMID: 26402672; Kidney Cancer. 2019 Feb 5;3(1):15-29, PMID: 30854496;