Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P01275 (glucagon)
 26,492 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. Glutaminase activity was measured in primary cultures of hepatocytes. 2. Enzyme activity decreased markedly after 24-40 h in culture, and this loss of activity was accompanied by loss of enzyme protein. 3. The loss of activity was delayed by high concentrations of glutamine, and was abolished by the continuous presence of NH4Cl in the culture medium. 4. In cells from rats fed on high-carbohydrate protein-free diet, glutaminase activity was increased by glucagon, but not by dexamethasone. This induction was observed only in the continuous presence of NH3 or high concentrations of glutamine. 5. It is concluded that NH3 and glutamine are essential for the stabilization and induction of glutaminase activity in hepatocytes. The inactivation of glutaminase in hepatocytes and in vivo under certain conditions may be due to lack of NH3 in the extracellular medium.
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PMID:Glucagon and ammonia influence the long-term regulation of phosphate-dependent glutaminase activity in primary cultures of rat hepatocytes. 200 Dec 24

1. Glutaminase and glutamine synthetase are simultaneously active in the intact liver, resulting in an energy consuming cycling of glutamine at a rate up to 0.2 mumol per g per min. 2. An increase in portal glutamine concentration was followed by an increased flux through glutaminase, but flux through glutamine synthetase remained unchanged. Glutaminase flux was also increased by ammonium ions or glucagon; these effects were additive. 3. Glutamine synthetase flux was increased by ammonium ions, but this activation was partly overcome by increasing portal glutamine concentrations. Glutamine synthetase flux was slightly increased by glucagon at portal glutamine concentrations of about 0.2-0.3 mM, but was strongly inhibited above 0.6 mMs. 4. During experimental metabolic acidosis there was an increased net release of glutamine by the liver, being due to opposing changes of flux through glutaminase and glutamine synthetase. Conversely, an increased glutamine uptake by the liver during metabolic alkalosis was observed due to an inhibition of glutamine synthetase and an activation of glutaminase. However, the two enzyme activities respond differently depending on whether glucagon or ammonium ions are present.
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PMID:Regulation of flux through glutaminase and glutamine synthetase in isolated perfused rat liver. 613 95

The liver of diabetic animals removes increased quantities of glutamine. We therefore examined factors that affect hepatic glutaminase activity in hepatocytes and mitochondria. Glutamine use, through glutaminase, was measured in isolated rat hepatocytes by monitoring the production of 14CO2 from [1-(14)C]glutamine. Hepatocytes from streptozotocin-induced diabetic rats use glutamine more rapidly than do hepatocytes from normal or insulin-maintained diabetic rats. Glutamine use in all of these hepatocytes was stimulated by glucagon and epinephrine. Glutaminase activity, assayed in broken mitochondrial membranes, was increased approximately 2.5-fold in diabetic rats. The sensitivity of glutaminase, measured in intact liver mitochondria, to phosphate was markedly left-shifted in mitochondria from diabetic rats compared with those from controls. In fact, glutaminase was increased 10-fold at 2.5 mmol/l phosphate compared with controls. This increased sensitivity of glutaminase to physiological concentrations of phosphate is characteristic of its hormonal activation. Therefore, activation of glutaminase plays a major role in diabetes and is as important as increases in its total enzyme amount in determining the increased glutamine uptake in diabetes.
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PMID:Regulation of hepatic glutaminase in the streptozotocin-induced diabetic rat. 939 78