Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.3.9 (glucose-6-phosphatase)
 3,081 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The classical role of glucose-6-phosphatase in liver and kidney is the production of glucose for release into blood. In liver, glucose-6-phosphatase catalyses the terminal step of glycogenolysis and gluconeogenesis. Abnormally low hepatic glucose-6-phosphatase activity is found in human genetic deficiencies i.e. glycogen storage disease type I and in cases of developmental delay, found predominantly in preterm infants. In contrast, abnormally high liver glucose-6-phosphatase occurs in poorly controlled or untreated diabetes mellitus. Hepatic glucose-6-phosphatase is an integral endoplasmic reticulum (and nuclear membrane) protein and it is part of a multicomponent system. Its active site is situated inside the lumen of the endoplasmic reticulum and transport proteins are needed to allow its substrates glucose-6-phosphate (and pyrophosphate) and its products phosphate and glucose to cross the endoplasmic reticulum membrane. In addition, a calcium binding protein is also associated with the glucose-6-phosphatase enzyme. Immunohistochemical studies, in combination with image analysis, have shown that glucose-6-phosphatase is present in liver and kidney and also in specific cell types in a variety of human tissues, for example Leydig cells in the testis and some astrocytes in the brain. Where practicable, enzymatic analysis, direct transport assays and/or immunological detection of the endoplasmic reticulum glucose and phosphate transport proteins have been used to demonstrate the presence and activity of the whole glucose-6-phosphatase system. The distribution of the human glucose-6-phosphatase system changes dramatically during development with a different spatial and temporal pattern in each tissue. The most unexpected localization was in circulating, predominantly nucleated, embryonic and early fetal red blood cells.
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PMID:The glucose-6-phosphatase system in human development. 857 17

Overproduction of glucose by the liver is the major cause of fasting hyperglycemia in both insulin-dependent and non-insulin-dependent diabetes mellitus. The distal enzymatic step in the process of glucose output is catalyzed by the glucose-6-phosphatase complex. We show here that 90% partially pancreatectomized diabetic rats have a >5-fold increase in the messenger RNA and a 3-4-fold increase in the protein level of the catalytic subunit of glucose-6-phosphatase in the liver. Normalization of the plasma glucose concentration in diabetic rats with either insulin or the glycosuric agent phlorizin normalized the hepatic glucose-6-phosphatase messenger RNA and protein within approximately 8 h. Conversely, phlorizin failed to decrease hepatic glucose-6-phosphatase gene expression in diabetic rats when the fall in the plasma glucose concentration was prevented by glucose infusion. These data indicate that in vivo gene expression of glucose-6-phosphatase in the diabetic liver is regulated by glucose independently from insulin, and thus prolonged hyperglycemia may result in overproduction of glucose via increased expression of this protein.
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PMID:Glucose regulates in vivo glucose-6-phosphatase gene expression in the liver of diabetic rats. 862 17

Using Northern blot with a specific glucose-6-phosphatase (Glc6Pase) cDNA probe and enzymatic activity determination, we studied the effect of streptozotocin-induced diabetes on Glc6Pase in rat gluconeogenic tissues. The Glc6Pase mRNA abundance was increased four to five times in both the liver and kidney of diabetic rats. This was correlated with a concomitant 130% increase in Glc6Pase catalytic subunit in both tissues. The elevated level of Glc6Pase mRNA was significantly corrected in both the liver and kidney of diabetic rats after a 12-h insulin treatment. We also studied Glc6Pase mRNA and activity in gluconeogenic tissues during the fed-fasted and fasted-refed transitions in normal rats. In the liver, the abundance of Glc6Pase mRNA was sharply increased about four times after 24 or 48 h of fasting. In the kidney, the Glc6Pase mRNA level was gradually increased some three and five times after 24 and 48 h of fasting, respectively. The increase of Glc6Pase mRNA in both organs was matched with a doubling of the activity of Glc6Pase catalytic subunit: rapid in the liver and gradual in the kidney. The liver Glc6Pase mRNA abundance in 48-h fasted rats was acutely and importantly decreased upon refeeding. The kidney Glc6Pase mRNA level was also significantly lowered under these conditions, albeit less rapidly. These data demonstrate that efficient control of Glc6Pase takes place in both gluconeogenic organs at the pretranslational level and suggest that insulin might play an important role in this control. In addition, using reverse transcription-polymerase chain reaction and Northern blot, we report that Glc6Pase mRNA is not detectable in several other tissues previously assumed to express the enzyme.
Diabetes 1996 Jul
PMID:Glucose-6-phosphatase mRNA and activity are increased to the same extent in kidney and liver of diabetic rats. 866 39

The mRNA level of the catalytic subunit of rat liver glucose-6-phosphatase (Glu-6-Pase) was regulated by hormones commensurate with activity changes in vivo. Insulin exerts a dominant negative effect on the mRNA levels of Glu-6-Pase. Both mRNA levels and activities of the enzyme are low in the fed and refed state where insulin levels are elevated. Insulin administration to diabetic rats also decreases levels of mRNA and Glu-6-Pase activity. Insulin at a concentration of 1 nmol/l completely overcomes the stimulatory effect of glucocorticoids on Glu-6-Pase message levels in FAO hepatoma cells. The stimulatory response to glucocorticoid in FAO cells is biphasic, with maxima seen at 3 and 18 h after hormone addition (respectively 1.6- and 3.3-fold). 8-(4-chlorophenylthio)-cAMP (CPT-cAMP) causes a fourfold increase in Glu-6-Pase mRNA at 3 h in FAO cells. The gene of rat liver Glu-6-Pase is 13 kilobases in length and comprised of 5 exons. The exon-intron structure is completely conserved when compared with the mouse and human genes. A 0.5-kb 3'-untranslated region, which is present in rat and mouse liver Glu-6-Pase cDNA, is absent in the Glu-6-Pase gene reported here, indicating the possible duplication of either the terminal fifth exon or the entire gene. The promoter region contains a consensus core CCAAT element at position -207 and a TATAAA at position -31. Several possible response elements have been identified in the 5'-flanking region (from a HindIII site at position -1641). A consensus glucocorticoid response element is located at base pair -1552, a 9/10 match of the insulin response sequence is located at position -1449, and a 7/8 match of the cAMP response element is located at position -164.
Diabetes 1996 Nov
PMID:Regulation of rat liver glucose-6-phosphatase gene expression in different nutritional and hormonal states: gene structure and 5'-flanking sequence. 886 62

Crude extracts containing the enzymes obtained from mouse liver were incubated with 3-deoxyglucosone (3-DG), and then subjected to assay of the activities of enzymes responsible for glucose metabolism. Hexokinase and glucose-6-phosphate dehydrogenase activities were decreased by 3-DG and hexokinase activity was strongly inhibited time and concentration dependently, while glucokinase, glucose-6-phosphatase, and phosphofructokinase activities were scarcely affected. These results suggest that 3-DG inhibits the intake of glucose in the liver and a connection with development of diabetes.
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PMID:Effect of 3-deoxyglucosone on the activities of enzymes responsible for glucose metabolism in mouse liver. 887 29

The distal enzymatic step in the process of glucose output is catalyzed by the glucose-6-phosphatase (Glc-6-Pase) complex. The recently cloned catalytic unit of this complex has been shown to be regulated by insulin, dexamethasone, cAMP, and glucose. Using a combination of intralipid and/or nicotinic acid infusions and a pancreatic clamp technique, we maintained plasma free fatty acids (FFAs) at three different levels (0.26 +/- 0.07, 0.56 +/- 0.09, and 1.59 +/- 0.12 mmol/l) in the presence of well-controlled hormonal and metabolic conditions. An increase in the plasma FFA concentration within the physiological range caused a rapid, greater than threefold increase in the mRNA and protein levels of the catalytic subunit of Glc-6-Pase in the liver. These data indicate that the in vivo gene expression of Glc-6-Pase in the liver is regulated by circulating lipids independent of insulin and thus that prolonged hyperlipidemia may contribute to the increased production of glucose via increased expression of this protein.
Diabetes 1997 Jan
PMID:Induction of hepatic glucose-6-phosphatase gene expression by lipid infusion. 897 Oct 97

The enzyme system glucose-6-phosphatase (EC 3.1.3.9) plays a major role in the homeostatic regulation of blood glucose. It is responsible for the formation of endogenous glucose originating from gluconeogenesis and glycogenolysis. Recently, chlorogenic acid was identified as a specific inhibitor of the glucose-6-phosphate translocase component (Gl-6-P translocase) of this enzyme system in microsomes of rat liver. Glucose 6-phosphate hydrolysis was determined in the presence of chlorogenic acid or of new synthesized derivatives in intact rat liver microsomes in order to assess the inhibitory potency of the compounds on the translocase component. Variation in the 3-position of chlorogenic acid had only poor effects on inhibitory potency. Introduction of lipophilic side chain in the 1-position led to 100-fold more potent inhibitors. Functional assays on isolated perfused rat liver with compound 29i, a representative of the more potent derivatives, showed a dose-dependent inhibition of gluconeogenesis and glycogenolyosis, suggesting glucose-6-phosphatase as the locus of interference of the compound for inhibition of hepatic glucose production also in the isolated organ model. Gl-6-P translocase inhibitors may be useful for the reduction of inappropriately high rates of hepatic glucose output often found in non-insulin-dependent diabetes.
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PMID:Chlorogenic acid and synthetic chlorogenic acid derivatives: novel inhibitors of hepatic glucose-6-phosphate translocase. 900 13

Female albino rats were exposed to methadone over a 35-day period by addition of the drug in their drinking water. The final dose of the drug was 1.8 mg/kg body weight per day. After this period, the drug was withdrawn from some animals for 30 days (postexposure). Compared to unexposed controls, serum glucose levels rose during exposure and returned to control levels postexposure. Oral glucose tolerance tests showed impairment in 35-day drug-exposed animals compared to controls and postexposure. The activities of three key enzymes of glycolysis and three key enzymes of gluconeogenesis were measured in liver during and at the end of the exposure period, as well as postexposure. Compared to unexposed controls and postexposure, specific activities of two glycolytic enzymes in livers of exposed animals-hexokinase and phosphofructokinase 1-were significantly reduced, whereas the activity of a third glycolytic enzyme-pyruvate kinase-was unchanged. The specific activities of two gluconeogenic enzymes-glucose-6-phosphatase and fructose-1,6-biphosphatase-were significantly elevated in the drug-exposed animals compared to controls, whereas the activity of a third enzyme-phosphoenolpyruvate carboxykinase-was unchanged. These data indicate that methadone addiction produces a metabolic state similar to insulin-resistant diabetes.
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PMID:Effect of methadone addiction on glucose metabolism in rats. 911 73

To elucidate cellular mechanisms of insulin resistance induced by excess dietary fat, we studied conscious chronically high-fat-fed (HFF) and control chow diet-fed rats during euglycemic-hyperinsulinemic (560 pmol/l plasma insulin) clamps. Compared with chow diet feeding, fat feeding significantly impaired insulin action (reduced whole body glucose disposal rate, reduced skeletal muscle glucose metabolism, and decreased insulin suppressibility of hepatic glucose production [HGP]). In HFF rats, hyperinsulinemia significantly suppressed circulating free fatty acids but not the intracellular availability of fatty acid in skeletal muscle (long chain fatty acyl-CoA esters remained at 230% above control levels). In HFF animals, acute blockade of beta-oxidation using etomoxir increased insulin-stimulated muscle glucose uptake, via a selective increase in the component directed to glycolysis, but did not reverse the defect in net glycogen synthesis or glycogen synthase. In clamp HFF animals, etomoxir did not significantly alter the reduced ability of insulin to suppress HGP, but induced substantial depletion of hepatic glycogen content. This implied that gluconeogenesis was reduced by inhibition of hepatic fatty acid oxidation and that an alternative mechanism was involved in the elevated HGP in HFF rats. Evidence was then obtained suggesting that this involves a reduction in hepatic glucokinase (GK) activity and an inability of insulin to acutely lower glucose-6-phosphatase (G-6-Pase) activity. Overall, a 76% increase in the activity ratio G-6-Pase/GK was observed, which would favor net hepatic glucose release and elevated HGP in HFF rats. Thus in the insulin-resistant HFF rat 1) acute hyperinsulinemia fails to quench elevated muscle and liver lipid availability, 2) elevated lipid oxidation opposes insulin stimulation of muscle glucose oxidation (perhaps via the glucose-fatty acid cycle) and suppression of hepatic gluconeogenesis, and 3) mechanisms of impaired insulin-stimulated glucose storage and HGP suppressibility are not dependent on concomitant lipid oxidation; in the case of HGP we provide evidence for pivotal involvement of G-6-Pase and GK in the regulation of HGP by insulin, independent of the glucose source.
Diabetes 1997 Nov
PMID:Mechanisms of liver and muscle insulin resistance induced by chronic high-fat feeding. 935 24

The molecular mechanisms underlying increased hepatic phosphoenolpyruvate carboxykinase (PEPCK) gene transcription and gluconeogenesis in type II diabetes are largely unknown. To examine the involvement of glucocorticoids and the cis-acting insulin response sequence (IRS, -416/-407) in the genetically obese db/db mouse model, we generated crosses between C57BL/KsJ-db/+ mice and transgenic mice that express -460 or -2000 base pairs of the rat PEPCK gene promoter containing an intact or mutated IRS, linked to a reporter gene. Transgenic mice expressing the intact PEPCK(460)-CRP (C-reactive protein) transgene bred to near homozygosity at the db locus were obese, hyperinsulinemic, and developed fasting hyperglycemia (389 +/- 26 mg/100 ml) between 4 and 10 weeks of age. Levels of CRP reporter gene expression were increased 2-fold despite severe hyperinsulinemia compared with non-diabetic non-obese transgenic mice. Reporter gene expression was also increased 2-fold in transgenic obese diabetic db/db mice bearing a mutation in the IRS, -2000(IRS)-hGx, compared with non-obese non-diabetic transgenic 2000(IRS)-hGx mice. Treatment of obese diabetic db/db transgenic mice with the glucocorticoid receptor blocker RU 486 decreased plasma glucose by 50% and reduced PEPCK, GLUT2, glucose-6-phosphatase, tyrosine aminotransferase, CRP, and hGx reporter gene expression to levels similar to those of non-obese normoglycemic transgenic mice. Taken together, these results establish that -460 bp of 5'-flanking sequence is sufficient to mediate the induction of PEPCK gene transcription in genetically obese db/db mice during the development of hyperglycemia. The results further demonstrate that the mechanism underlying increased expression of gluconeogenic enzymes in the db/db mouse requires the action of glucocorticoids and occurs independently of factors acting through the PEPCK IRS (-416/-407) promoter binding site.
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PMID:Phosphoenolpyruvate carboxykinase (GTP) gene transcription and hyperglycemia are regulated by glucocorticoids in genetically obese db/db transgenic mice. 939 82


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