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)

Glycoprotein processing in Dictyostelium discoideum is characterized by enzyme catalyzed steps not reported in other organisms. One of these is the formation of a beta 1 --> 4 linkage between GlcNAc and the mannose linked to the core mannose in the alpha 1 --> 6 position of N-glycosides. A simple and sensitive assay for this GlcNAc transferase activity, using a tri-mannose acceptor and a low concentration of UDP-GlcNAc, was developed. Homogenates of the organism were subjected to sub-cellular fractionation by centrifugation in discontinuous sucrose gradients. The specific activity was enriched 4-5-fold in a crude membrane fraction. The transferase was purified 10-12-fold in a membrane fraction that bands on top of 1.1 M sucrose. This fraction was also enriched in nucleotidyldiphosphatase. The enriched fraction was deficient in glucose-6-phosphatase, an endoplasmic reticulum marker. Approx. 80% of the transferase activity was latent, and unavailable to protease. Purified membranes were either subjected to phase separation in Triton X-114, or sodium carbonate extraction or sonication. In each case, the transferase behaved as an intrinsic membrane protein. Several secreted and lysosomal proteins are modified by the enzyme. These data support the idea that the GlcNAc transferase is present as an integral Golgi membrane protein and that at least the catalytic center of the transferase is on the lumenal side of the vesicles.
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PMID:Subcellular distribution of "intersecting' beta-N-acetylglucosaminyltransferase in Dictyostelium discoideum. A likely marker for the Golgi apparatus. 865 99

We have studied the effects of fatty-acyl-CoA esters on the activity of glucose-6-phosphatase (Glc6Pase) in untreated and detergent-treated liver microsomes. Fatty-acyl-CoA esters with chain lengths less than or equal to nine carbons do not inhibit Glc6Pase. Medium-chain fatty-acyl-CoA esters (10-14 carbons) inhibit Glc6Pase of untreated microsomes in a dose-dependent manner in the range 1-20 microM. The inhibitory effect is also dependent on the acyl-chain length. The higher the chain length, the stronger the inhibitory effect. It is also dependent on the microsomal protein concentration. The higher the protein concentration, the lower the inhibitory effect. Fatty-acyl-CoA esters with longer chain length (equal to or higher than 16 carbons) inhibit Glc6Pase of untreated microsomes within the range 1-2 microM. However, the inhibitory effect is either partially or totally cancelled, or even changed into an activation effect at higher concentrations. This is due to the release of mannose-6-phosphatase latency. The inhibition is fully reversible in the presence of bovine serum albumin. The mechanism of the Glc6Pase inhibition in untreated microsomes is uncompetitive (Ki for myristoyl-CoA = 1.2 +/- 0.3 microM, mean +/- SD, n = 3). Glc6Pase of detergent-treated microsomes is also inhibited by fatty-acyl-CoA esters, albeit less efficiently. In this case, the mechanism is non-competitive (Ki for myristoyl-CoA = 29 +/- 3 microM).
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PMID:Mechanisms by which fatty-acyl-CoA esters inhibit or activate glucose-6-phosphatase in intact and detergent-treated rat liver microsomes. 865 31

Glycogen storage disease type Ia (GSD Ia, von Gierke disease) is an autosomal recessive inborn error of metabolism caused by the deficiency of D-glucose-6-phosphatase (G6Pase). Since this enzyme is expressed primarily in hepatocytes, couples at risk for GSD type Ia relied on fetal liver biopsy for prenatal diagnosis. The recent isolation of the G6Pase gene and identification of several disease-causing mutations have permitted molecular prenatal diagnosis using amniocytes or chorionic villi. Chorionic villus sampling (CVS) was performed in an Ashkenazi Jewish family in whom a previous child was homoallelic and both parents were heterozygous for the R83C mutation. Molecular analysis revealed that the fetus was not affected. The prenatal diagnosis was confirmed postnatally by biochemical and molecular studies. Thus, the molecular prenatal diagnosis of GSD type Ia can be safely and accurately made in the first trimester.
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PMID:Molecular prenatal diagnosis of glycogen storage disease type Ia. 873 7

We investigated the kinetics of 2-deoxy-D-glucose (DG) uptake and metabolism in Caco-2 cells, because this human cell line may represent a valid enterocyte model to assess the dynamics between sugar transport and metabolism and hence to obtain insights into the factors involved during the intracellular phase of glucose absorption. When studied in 14-day-old monolayers, DG uptake is characterized by a lag phase with a time course matching the decrease in intracellular glucose concentrations, and no intracellular glucose 6-phosphate (G-6-P) can be detected at any time during incubation. After 1 h of preincubation of Caco-2 cells in substrate-free transport medium, however, steady-state DG uptake matches 2-deoxy-D-glucose 6-phosphate (DG-6-P) accumulation with undetectable levels of free DG. This complex behavior in DG uptake is linked to high hexokinase activity in Caco-2 cells, and the enzyme has a Michaelis-Menten constant K(m) for glucose that is typical of hexokinase type II (0.120 +/- 0.003 mM). Caco-2 cells also contain low-level glucose-6-phosphatase (G-6-Pase) activity, which may account for the leveling off in DG uptake, and the kinetics of DG transport may be attributed to the existence of a predominant pathway with a K(m) of 1.7 +/- 0.2 mM. Finally, analysis of the growth-related expression of DG transport and hexokinase activity clearly shows that DG uptake is lowest in postconfluent cells when hexokinase is at its highest levels. We thus conclude that 1) transport is the rate-limiting step during DG accumulation, 2) G-6-P is a potent inhibitor of hexokinase activity compared with DG-6-P, so that enzyme inhibition may have physiological relevance in diverting glucose from metabolism during its active reabsorption in the small intestine, and 3) low levels of G-6-Pase activity seem to exclude this enzyme, and hence the endoplasmic reticulum, as important factors during the intracellular phase of glucose transport.
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PMID:2-Deoxyglucose transport and metabolism in Caco-2 cells. 877 13

The development of new diagnostic/therapeutic modalities for cancer requires a specific understanding of how tumors differ from normal tissues. Though the key components involved in the selective accumulation of 2-deoxy-D-glucose (2-DG) analogs in tumors are known, the relative importance of each is controversial. For this reason glucose transport protein (GLUT) density, hexokinase/glucose-6-phosphatase (GP) activity, and 2-DG biodistribution were measured together in four tumor models and normal murine tissues. Direct binding studies with 3H-cytochalasin B showed that GLUT density was elevated 20-fold in LX-1 tumors. Immunohistochemically in all tumors, the expression of GLUT-1 was highest in the necrotic/ perinecrotic foci and similar in cells not adjacent to necrotic foci. As the retention of 3H-2-DG was similar in all tumors, these data suggest that the GLUT-1 in perinecrotic tumor cells were not rate limiting for 3H-2-DG uptake. Kidney, liver, and lung had high GP activity and rapid clearance of 3H-2-DG. Sodium orthovanadate (5 mumol), a GP inhibitor, increased the concentration of 3H-2-DG in these tissues, suggesting that GP is a rate-limiting enzyme for 3H-2-DG clearance. All tumor homogenates had low GP activity, and hexokinase activity was not elevated compared to normal tissues. Thus, in the tumors studied, the selective accumulation of 3H-2-DG consistently occurred in the absence of significant GP activity without the marked overexpression of hexokinase or GLUT.
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PMID:The interaction among glucose transport, hexokinase, and glucose-6-phosphatase with respect to 3H-2-deoxyglucose retention in murine tumor models. 883 12

The effect of 2-deoxy-D-glucose (2DG) and vitamin E on the alterations in glucose metabolism induced by perchloroethylene (PER) was studied in mice. Oral administration of PER (3 g kg-1 body wt. day-1) in sesame oil for 15 days caused a significant increase in liver weight, degeneration/necrosis of hepatocytes and increase in kidney weight, glomerular nephrosis and degeneration. These changes occurred concurrently with a significant decrease in blood glucose level, elevated activities of hexokinase, aldolase and phosphoglucoisomerase and decreased activity of gluconeogenic enzymes (glucose-6-phosphatase and fructose-1,6-diphosphatase), indicating the sensitivity of liver and kidney as target tissues in PER toxicity. Evidence is presented that both 2DG (500 mg kg-1 body wt. day-1 i.p.) and vitamin E (400 mg kg-1 body wt. day-1 by oral gavage) during concomitant administration prevented most of the above PER-induced biochemical and pathological alterations. These results suggest that early metabolic and pathological perturbations following exposure of PER in mice can provide the basis for its documented potential for chronic effects like cytotoxicity and may be involved in modulation of carcinogenicity.
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PMID:Perchloroethylene-induced alterations in glucose metabolism and their prevention by 2-deoxy-D-glucose and vitamin E in mice. 885 21

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

Cultured astroglial cells are able to utilize the monosaccharides glucose, mannose, or fructose as well as the sugar alcohol sorbitol as energy fuel. Astroglial uptake of the aldoses is carrier-mediated, whereas a non-saturable transport mechanism is operating for fructose and sorbitol. The first metabolic step for all sugars, including fructose being generated by enzymatic oxidation of sorbitol, is phosphorylation by hexokinase. Besides glucose only mannose may serve as substrate for build-up of astroglial glycogen. Whereas glycogen synthase appears to be present in astrocytes as well as neurons, the exclusive localization of glycogen phosphorylase in astrocytes and ependymal cells of central nervous tissue correlates well with the occurrence of glycogen in these cells. The identification of lactic acid rather than glucose as degradation product of astroglial glycogen appears to render the presence of glucose-6-phosphatase in cultured astrocytes an enigma. The colocalization of pyruvate carboxylase, phosphenolpyruvate carboxykinase and fructose-1,6-bisphosphatase points to astrocytes as being the gluconeogenic cell type of the CNS.
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PMID:Metabolic pathways for glucose in astrocytes. 929 44

Measurement of hepatic glucose production (HGP) by standard isotope dilution reveals only the net release of glucose from the liver, not the flux across glucose-6-phosphatase ([G6Pase] or total hepatic glucose output), hepatic glucose cycling (HGC), irreversible glucose disposal into glycogen in the liver (hepatic Rd), or net hepatic glucose balance. We describe two independent isotopic techniques for measuring these parameters in vivo, both of which use secreted glucuronate (GlcUA). HGC can be quantified by measuring a correction factor for glucose label retained in hepatic glucose-6-phosphate (G6P), sampled as GlcUA. A complementary technique for measuring total hepatic glucose output is also described (reverse dilution), requiring administration of no labeled glucose but instead a labeled gluconeogenic precursor and unlabeled glucose. Hepatic Rd is calculated by multiplying the rate of appearance (Ra) of hepatic UDP-glucose ([UDP-glc] based on dilution of labeled galactose in GlcUA) times the direct entry of glucose into hepatic UDP-glc and the fraction of labeled UDP-glc retained in the liver. The sum of hepatic Rd plus HGC represents the total hepatic glucose phosphorylation rate. Rats received intravenous (i.v.) glucose infusions at a rate of 15 to 30 mg/kg/min after a 24-hour fast. Despite a suppression of net HGP more than 50%, total hepatic glucose output was not significantly decreased, because of increased HGC. Total hepatic glucose output calculated by reverse dilution yielded similar results during i.v. glucose infusions at 15 mg/kg/min, although values were higher than obtained by the correction-factor method at 30 mg/kg/min. The fraction of labeled UDP-glc released into blood glucose, representing a hepatic glycogen cycle, decreased from 35% (fasted) to nearly 0% (i.v. glucose 30 mg/kg/min). Hepatic Rd was 1.4, 4.6, and 7.5 mg/kg/min (fasted and i.v. glucose 15 and 30 mg/kg/min, respectively); total hepatic glucose phosphorylation increased substantially (from 4.2 to 8.5 to 12.7 mg/kg/min) and net hepatic glucose balance changed from negative to positive during i.v. glucose. In conclusion, hepatic G6Pase flux, glucose phosphorylation, HGC, disposal of glucose into glycogen, and net glucose balance can be measured noninvasively in vivo under various metabolic conditions by techniques involving the GlcUA probe.
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PMID:Hepatic glucose-6-phosphatase flux and glucose phosphorylation, cycling, irreversible disposal, and net balance in vivo in rats. Measurement using the secreted glucuronate technique. 943 32

S 5627 is a synthetic analogue of chlorogenic acid. S 5627 is a potent linear competitive inhibitor of glucose 6-phosphate (Glc-6-P) hydrolysis by intact microsomes (Ki = 41 nM) but is without effect on the enzyme in detergent- or NH4OH-disrupted microsomes. 3H-S 5627 was synthesized and used as a ligand in binding studies directed at characterizing T1, the Glc-6-P transporter. Binding was evaluated using Ca2+-aggregated microsomes, which can be sedimented at low g forces. Aside from a modest reduction in K values for both substrate and S 5627, Ca2+ aggregation had no effect on glucose-6-phosphatase (Glc-6-Pase). Scatchard plots of binding data are readily fit to a simple "two-site" model, with Kd = 21 nM for the high affinity site and Kd = 2 microM for the low affinity site. Binding to the high affinity site was competitively blocked by Glc-6-P (Ki = 9 microM), whereas binding was unaffected by mannose-6-phosphate, Pi, and PPi and only modestly depressed by 2-deoxy-D-glucose 6-phosphate, a poor substrate for Glc-6-Pase in intact microsomes. Thus the high affinity 3H-S 5627 binding site fits the criteria for T1. Permeabilization of the membrane with 0.3% (3-[(chloramidopropyl)-dimethylammonio]-1-propanesulfonate) activated Glc-6-Pase and broadened its substrate specificity, but it did not significantly alter the binding of 3H-S 5627 to the high affinity sites or the ability of Glc-6-P to block binding. These data demonstrate unequivocally that two independent Glc-6-P binding sites are involved in the hydrolysis of Glc-6-P by intact microsomes. The present findings are the strongest and most direct evidence to date against the notion that the substrate specificity and the intrinsic activity of Glc-6-Pase in native membranes are determined by specific conformational constraints imposed on the enzyme protein. These data constitute compelling evidence for the role of T1 in Glc-6-Pase activity.
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PMID:Direct evidence for the involvement of two glucose 6-phosphate-binding sites in the glucose-6-phosphatase activity of intact liver microsomes. Characterization of T1, the microsomal glucose 6-phosphate transport protein by a direct binding assay. 949 46


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