Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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 purpose of the present study was to develop a technique to identify, isolate and partially purify these membrane bound compartments for further characterizations of their Ca2+ transport and storage mechanisms. We 45Ca(2+)-loaded the agonist-sensitive Ca2+ stores in rat pancreatic acini. The loading was accomplished by first depleting the stores with carbachol stimulation followed by the addition of 45Ca2+ and atropine to the extracellular media. After homogenization of the 45Ca(2+)-loaded acini, subcellular fractions were resolved on sucrose and Nycodenz gradients. 45Ca2+ fluxes were minimized during these procedures by inclusion in the media of LaCl3. Five subcellular fractions were identified that specifically accumulated 45Ca2+ after carbachol stimulation. Electron microscopic observations of the fractions demonstrated that three of the fractions consisted of rough membrane vesicles; that one consisted of a mixture of rough and smooth membrane vesicles; and that one consisted of smooth membrane vesicles. All fractions were enriched in glucose-6-phosphatase. All 5 fractions demonstrated ATP dependent 45Ca2+ uptake. By Western blot analysis, all fractions contained calnexin, p58, sarcoplasmic reticulum type Ca(2+)-ATPase, and IP3 receptor. These results demonstrated that the 45Ca(2+)-loading technique can be used to isolate and characterize distinct compartments of the agonist-sensitive Ca2+ store in the pancreatic acinar cell.
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PMID:Isolation of subcellular agonist-sensitive calcium stores from the pancreatic acinar cell. 858 65

In rats injected with bacterial lipopolysaccharide (LPS; 5 gamma mg/g body weight [BWT]), the toxin provokes death within 24 h in 23% of the animals and, in surviving rats, causes a decrease in BWT, hyperlactacidemia, hyperlipacidemia, and hyperketonemia, as well as depletion of both liver and muscle glycogen content. In the liver, LPS severely lowers the ATP and total adenine nucleotide content, ATP/ADP ratio, and adenylate charge. In hepatocytes from LPS-injected rats, the oxidation of D-glucose is first increased 2 h after administration of the toxin, despite close-to-normal phosphorylation of the hexose. In hepatocytes prepared from rats killed 24 h after injection of LPS, the phosphorylation of D-glucose, its incorporation into glycogen, and its oxidation are all severely impaired. This sequence of changes, which coincides with a decreased ratio between pyruvate and lactate production from exogenous D-glucose, is comparable to that found with agents that uncouple oxidative phosphorylation. The injection of LPS also alters the metabolic response of hepatocytes to the dimethyl ester of succinic acid (SAD), in terms, for instance, of the sparing action of the ester upon both the production of 14CO2 by hepatocytes prelabeled with L-[U-14C] glutamine and the output of NH4+, and its inhibitory action on glycogenolysis and futile cycling in the reactions catalyzed by glucokinase and glucose-6-phosphatase. Nevertheless, the infusion of SAD protects the rats against the deleterious effect of LPS upon such variables as the plasma concentration of free fatty acids and beta-hydroxybutyrate, the liver ATP content, and the oxidation of D-glucose, as well as the pyruvate/lactate ratio, in hepatocytes prepared from the LPS-injected rats. The infusion of SAD also virtually suppresses lethality in the LPS-injected animals. It is proposed, therefore, that the infusion of succinic acid esters may represent a novel therapeutic approach in endotoxemia and multiple-organ failure.
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PMID:Protective effects of succinic acid dimethyl ester infusion in experimental endotoxemia. 917 84

Microsomes prepared from three rat tissues were examined for their ability to import glucose-6-phosphate (G-6-P). Microsomes from liver, which possess a high level of glucose-6-phosphatase activity, were compared with those from cerebral cortex and cardiac muscle, which are not involved in the export of glucose and in which glucose-6-phosphatase activity is relatively low. In all three, a selective permeability to G-6-P was detected by light scattering. However, the sugar-phosphate specificity of the transport process differed. G-6-P was able to enhance ATP-dependent Ca2+ sequestration in all three types of microsomes. In addition, enzymatic detection of G-6-P after the rapid filtration of microsomes determined that, in the absence of Ca2+ and ATP, a level of intramicrosomal G-6-P approaching a passive equilibrium with the extramicrosomal G-6-P concentration was rapidly achieved in all three tissues. However, under conditions in which Ca2+ was being actively accumulated, the intramicrosomal levels of G-6-P exceeded the equilibrium value by three- to fourfold. This enhanced sequestration was not observed in the presence of Ca2+ or ATP alone or in the presence of a Ca2+ ionophore or an inhibitor of the microsomal Ca2+ ATPase. These data are consistent with a selective import pathway into the endoplasmic/sarcoplasmic reticulum for G-6-P independent of glucose-6-phosphatase activity. In addition, they suggest an alternate explanation for the enhanced sequestration of Ca2+ by the endoplasmic/sarcoplasmic reticulum of intact cells seen when extracellular glucose is increased.
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PMID:Glucose-6-phosphate and Ca2+ sequestration are mutually enhanced in microsomes from liver, brain, and heart. 960 62

When tested in the presence of an inhibitor of sorbitol dehydrogenase, both mannitol and sorbitol caused a progressive inhibition of the detritiation of [2-3H]glucose in isolated rat hepatocytes. The purpose of the present work was to investigate the possibility that this effect was mediated by the regulatory protein of glucokinase. When added to hepatocytes, mannitol decreased the apparent affinity of glucokinase for glucose and increased the concentration of fructose required to stimulate detritiation, without affecting the concentration of fructose 1-phosphate. Its effect could be attributed to the formation of mannitol 1-phosphate, a potent agonist of the regulatory protein, which, similarly to fructose 6-phosphate, reinforces its inhibitory action. Formation of mannitol 1-phosphate in hepatocytes was dependent on the presence of mannitol and was stimulated by compounds that increase the concentration of glucose 6-phosphate. Liver extracts catalysed the conversion of mannitol to mannitol 1-phosphate about 7 times more rapidly in the presence of glucose 6-phosphate than of ATP. The glucose 6-phosphate-dependent formation was entirely accounted for by a microsomal enzyme, glucose-6-phosphatase and was not due to a loss of latency of this enzyme. In hepatocytes in primary culture, mannitol decreased the detritiation rate and counteracted the effect of fructose to stimulate glucokinase translocation. Taken together, these results strongly support a central role played by the regulatory protein in the control of glucokinase activity and translocation in the liver, as well as a feedback control exerted by fructose 6-phosphate on this enzyme.
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PMID:Mannitol 1-phosphate mediates an inhibitory effect of mannitol on the activity and the translocation of glucokinase in isolated rat hepatocytes. 972 98

The inhibitory effects of the traditional herbal medicine Jindangwon (JDW) on streptozotocin (ST)-induced diabetic mellitus were studied using the ST-treated diabetic model. Glucokinase activity of pancreatic islets was severely impaired by ST treatment. However, when ST-treated islets were treated with 1 mg/ml of JDW, the enzyme activities of glucokinase and hexokinase were protected, glucose-6-phosphatase was not. When the effects of JDW on ST-induced ATP/ADP ratio of islets were assayed, JDW was effective in restoring of ATP/ADP ratio. In addition, ST decreased the enzyme activities of PDH, while JDW had a protective effect on the enzyme. ST-induced cGMP accumulation was significantly inhibited by JDW treatment. Furthermore, ST-induced nitrite formation was significantly inhibited by JDW treatment. JDW also showed the suppressed nitrite production in ST-treated pancreatic islet cells. When the islets (200/condition) were treated with ST (5 mM for 30 min), and then JDW was added to the ST-treated cells, 1.0 mg/ml of JDW showed the activated and recovered aconitase activity in pancreatic islet cells. When the effect of ST on the gene expression of pancreatic GLUT2 and glucokinase were examined, the level of GLUT2 and glucokinase mRNA in pancreatic islets was significantly decreased. However, JDW protected and improved the expression of protein and genes, indicating that JDW is effective on ST-induced inhibition of gene expression of GLUT2, glucokinase and proinsulin in islets. These results suggested that JDW is effective in this model to treat ST-induced diabetes.
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PMID:Effect of Jindangwon on streptozotocin-induced diabetes. 1097 94

In models of type 2 diabetes the expression of beta-cell genes is altered, but these changes have not fully explained the impairment in beta-cell function. We hypothesized that changes in beta-cell phenotype and global alterations in both carbohydrate and lipid pathways are likely to contribute to secretory abnormalities. Therefore, expression of genes involved in carbohydrate and lipid metabolism were analyzed in islets 4 weeks after 85-95% partial pancreatectomy (Px) when beta-cells have impaired glucose-induced insulin secretion and ATP synthesis. Px rats after 1 week developed mild to severe hyperglycemia that was stable for the next 3 weeks, whereas neither plasma triglyceride, non-esterified fatty acid, or islet triglyceride levels were altered. Expression of peroxisome proliferator-activated receptors (PPARs), with several target genes, were reciprocally regulated; PPARalpha was markedly reduced even at low level hyperglycemia, whereas PPARgamma was progressively increased with increasing hyperglycemia. Uncoupling protein 2 (UCP-2) was increased as were other genes barely expressed in sham islets including lactate dehydrogenase-A (LDH-A), lactate (monocarboxylate) transporters, glucose-6-phosphatase, fructose-1,6-bisphosphatase, 12-lipoxygenase, and cyclooxygenase 2. On the other hand, the expression of beta-cell-associated genes, insulin, and GLUT2 were decreased. Treating Px rats with phlorizin normalized hyperglycemia without effecting plasma fatty acids and reversed the changes in gene expression implicating the importance of hyperglycemia per se in the loss of beta-cell phenotype. In addition, parallel changes were observed in beta-cell-enriched tissue dissected by laser capture microdissection from the central core of islets. In conclusion, chronic hyperglycemia leads to a critical loss of beta-cell differentiation with altered expression of genes involved in multiple metabolic pathways diversionary to normal beta-cell glucose metabolism. This global maladaptation in gene expression at the time of increased secretory demand may contribute to the beta-cell dysfunction found in diabetes.
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PMID:Genetic regulation of metabolic pathways in beta-cells disrupted by hyperglycemia. 1178 87

Using insulin-secreting cells, we previously demonstrated that specific proteins associated with the cytosolic, secretory granule, and mitochondrial fractions undergo a novel type of phosphorylation on their histidine residues. Subsequently, we identified these proteins as the nucleoside diphosphate kinase (NDPK) [Kowluru and Metz, Biochemistry 1994;33:12495-503], the beta subunit of trimeric GTP-binding proteins [Kowluru et al., Biochem J 1996;313:97-107], and the alpha subunit of succinyl-CoA synthetase [Kowluru, Diabetologia 2001;44:89-94], respectively. Since several other enzymes of intermediary metabolism (e.g. ATP-citrate lyase and glucose-6-phosphatase) also undergo histidine phosphorylation, these initial findings may have a more generalized significance to beta cells. Herein, we characterized a novel protein histidine kinase in pancreatic beta cells, and determined it to be acid- and heat-labile as well as alkali-resistant in its phosphorylation of histone 4. Such an activity was detected in normal rat islets, human islets, and clonal beta (HIT-T15 and INS-1) cells, and could utilize either ATP or GTP as a phosphoryl donor (with K(m) values in the range of 60-100 microM). On a size-exclusion column, its molecular mass was estimated to be in the range of 60-70 kDa. It was stimulated by divalent cations (Mg(2+)>Mn(2+)>control=Ca(2+)=Zn(2+)=Co(2+)), but was resistant to polyamines. It was inactivated by known in vitro inhibitors of protein histidine phosphorylation (e.g. UDP or cromoglycate). Mastoparan, a global activator of G-proteins and insulin secretion from isolated beta cells, but not mastoparan-17, its inactive analog, stimulated histidine kinase activity and histidine phosphorylation of G(beta) subunit and insulin secretion from isolated rat islets. These studies identify, for the first time, a protein kinase activity in the pancreatic beta cell that does not act on traditional -Ser, -Tyr, or -Thr residues. They also establish a possible link between histidine kinase activity and G(beta) phosphorylation in isolated beta cells.
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PMID:Identification and characterization of a novel protein histidine kinase in the islet beta cell: evidence for its regulation by mastoparan, an activator of G-proteins and insulin secretion. 1211 Mar 68

The effects of benfluorex and two of its metabolites (S 422-1 and S 1475-1) on fatty acid and glucose metabolic fluxes and specific gene expression were studied in hepatocytes isolated from 24-h fasted rats. Both benfluorex and S 422-1 (0.1 or 1 mmol/l) reduced beta-oxidation rates and ketogenesis, whereas S 1475-1 had no effect. At the same concentration, benfluorex and S 422-1 were more efficient in reducing gluconeogenesis from lactate/pyruvate than S 1475-1. Benfluorex inhibited gluconeogenesis at the level of pyruvate carboxylase (45% fall in acetyl-CoA concentration) and of glyceraldehyde-3-phosphate dehydrogenase (decrease in ATP/ADP and NAD(+)/NADH ratios). Accordingly, neither benfluorex nor S 422-1 inhibited gluconeogenesis from dihydroxyacetone, but both stimulated gluconeogenesis from glycerol. In hepatocytes cultured in the presence of benfluorex or S 422-1 (10 or 100 micromol/l), the expression of genes encoding enzymes of fatty acid oxidation (carnitine palmitoyltransferase [CPT] I), ketogenesis (hydroxymethylglutaryl-CoA synthase), and gluconeogenesis (glucose-6-phosphatase, PEPCK) was decreased, whereas mRNAs encoding glucokinase and pyruvate kinase were increased. By contrast, Glut-2, acyl-CoA synthetase, and CPT II gene expression was not affected by benfluorex or S 422-1. In conclusion, this work suggests that benfluorex mainly via S 422-1 reduces gluconeogenesis by affecting gene expression and metabolic status of hepatocytes.
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PMID:Effects of benfluorex on fatty acid and glucose metabolism in isolated rat hepatocytes: from metabolic fluxes to gene expression. 1214 46

beta cell dysfunction is an important component of type 2 diabetes, but the molecular basis for this defect is poorly understood. The transcriptional coactivator PGC-1alpha mRNA and protein levels are significantly elevated in islets from multiple animal models of diabetes; adenovirus-mediated expression of PGC-1alpha to levels similar to those present in diabetic rodents produces a marked inhibition of glucose-stimulated insulin secretion from islets in culture and in live mice. This inhibition coincides with changes in metabolic gene expression associated with impaired beta cell function, including the induction of glucose-6-phosphatase and suppression of GLUT2, glucokinase, and glycerol-3-phosphate dehydrogenase. These changes result in blunting of the glucose-induced rise in cellular ATP levels and membrane electrical activity responsible for Ca(2+) influx and insulin exocytosis. These results strongly suggest that PGC-1alpha plays a key functional role in the beta cell and is involved in the pathogenesis of the diabetic phenotype.
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PMID:Suppression of beta cell energy metabolism and insulin release by PGC-1alpha. 1285 53

Substrate (futile) cycling involving carbohydrate turnover has been widely reported in plant tissues, although its extent, mechanisms, and functions are not well known. In this study, two complementary approaches, short and steady-state labeling experiments, were used to analyze glucose metabolism in maize (Zea mays) root tips. Unidirectional rates of synthesis for storage compounds (starch, Suc, and cell wall polysaccharides) were determined by short labeling experiments using [U-14C]glucose and compared with net synthesis fluxes to determine the rate of glucose production from these storage compounds. Steady-state labeling with [1-(13)C]glucose and [U-13C]glucose showed that the redistribution of label between carbon C-1 and C-6 in glucose is close to that in cytosolic hexose-P. These results indicate a high resynthesis flux of glucose from hexose-P that is not accounted for by glucose recycling from storage compounds, thus suggesting the occurrence of a direct glucose-P-to-glucose conversion. An enzyme assay confirmed the presence of substantial glucose-6-phosphatase activity in maize root tips. This new glucose-P-to-glucose cycle was shown to consume around 40% of the ATP generated in the cell, whereas Suc cycling consumes at most 3% to 6% of the ATP produced. The rate of glucose-P cycling differs by a factor of 3 between a maize W22 line and the hybrid maize cv Dea, and is significantly decreased by a carbohydrate starvation pretreatment.
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PMID:A new substrate cycle in plants. Evidence for a high glucose-phosphate-to-glucose turnover from in vivo steady-state and pulse-labeling experiments with [13C]glucose and [14C]glucose. 1602 83


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