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 interaction of glycoproteins of rough and smooth microsomal and Golgi membranes with Sepharose-bound lectins has been studied. One of these lectins was a crude preparation from wheat germ lipase which was found to bind primarily to N-acetyl neuraminic acid. Rough microsomes, smooth microsomes and Golgi membranes contain glycoproteins which bind to Concanavalin A (Con A specific for mannose residues) in decreasing amounts in the order indicated (rough, smooth and Golgi) and to wheat germ agglutinin (WGA, glucosamine-specific) and to the crude lipase preparation in increasing amounts in the order indicated. The small amount of binding of rough microsomes and Golgi membranes to Crotalaria (galactose-specific) increases substantially after neuraminidase treatment. Three submicrosomal particle preparations enriched either in AMPase or in NADH- or NADPH-oxidizing electron-transport enzymes contain glycoproteins which bind Con A and wheat germ agglutinin. The latter binding is sensitive to neuraminidase treatment. Two other submicrosomal particle preparations, both enriched in glucose-6-phosphatase activity, bind preferentially to WGA. This binding is, however, not sensitive to neuraminidase. Prolonged incubation with Ervilia lectin (mannose-specific) inhibits NADH-ferricyanide reductase activity, while the electron-transport chain involving cytochrome b5 is also inhibited by Crotalaria, indicating that both the flavoprotein and the cytochrome b5 are glycoproteins whose oligosaccharide chains have terminal mannose or galactose residues.
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PMID:Interaction of lectins with proteins of the endoplasmic reticulum and Golgi system of rat liver. 52 77

We describe the successful isolation and maintenance of primary cultures of dog gallbladder epithelial cells. The surgically removed gallbladder was treated with trypsin/EDTA for 45 minutes and epithelial cells were collected and resuspended in Eagle's minimum essential medium with 10% fetal calf serum, and plated on Vitrogen-coated culture dishes. Each gallbladder yielded approximately 12 to 15 x 10(6) columnar epithelial cells, greater than 95% of which were viable by trypan blue exclusion. In culture, cells maintained their polarity. They were arranged and grew in small and tight clusters that coalesced at confluency. When examined using transmission electron microscopy, prominent and numerous microville were identified on the apical portion of the plasma membrane. Cells were connected by well-formed desmosomes. Scanning electron microscopy revealed clusters of polyhedral cells with numerous papillary projections. Immunohistochemical studies demonstrated uniform staining of cells to keratin 35BH11 and AE1. Histochemical studies were positive for gamma-glutamyl transpeptidase and negative for glucose-6-phosphatase and albumin. Cells incorporated [3H]uridine into intracellular proteins and [14C]glucosamine into tissue and secreted mucous glycoproteins linearly over 2 to 24 hours. Flow cytometry studies demonstrated a consistent and reproducible number of cells (10 to 12%) at S-phase. However, the number of cells at S-phase was dramatically reduced to almost negligible as cells reached confluency. This method of culturing primary dog gallbladder epithelial cells is highly reproducible and reliable. These cells preserve their state of differentiation, polarity, histochemical and immunohistochemical profile, morphologic, and metabolic integrity with repeated passaging or after being frozen. [3H]Thymidine uptake is well maintained, although doubling time shows a trend of decreased cell duplication with time. This technique offers the opportunity to study the electrophysiologic, metabolic, and immunologic properties of epithelial cells.
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PMID:Long-term culture and partial characterization of dog gallbladder epithelial cells. 170 26

Zonal centrifugation has been used to isolate a fraction from bovine liver which appears to be derived from the Golgi apparatus. Morphologically, the fraction consists mainly of sacs and tubular elements. Spherical inclusions, probably lipoproteins, are occasionally seen in negative stains of this material. The preparation is biochemically unique. UDP-galactose:N-acetyl glucosamine, galactosyl transferase activity is concentrated about 40-fold in this fraction compared to the homogenate. Rotenone- or antimycin-insensitive DPNH- or TPNH- cytochrome c reductase activities are 60-80% of the level of activities found in microsomes. Purified organelles from bovine liver such as plasma membranes, rough microsomes, mitochondria and nuclei have negligible levels of galactosyl transferase. Some activity is present in smooth microsomes but at a level compatible with the possible presence of Golgi membranes in this fraction. The Golgi fraction does not contain appreciable amounts of enzymes such as ATPase, 5'-nucleotidase, glycosidase, glucose-6-phosphatase, acid phosphatase, or succinate-cytochrome c reductase. Similar fractions isolated from bovine epididymis also have very high levels of galactosyl transferase. The fraction is heavily osmicated when incubated for long periods of time at elevated temperatures, a characteristic property of Golgi membranes.
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PMID:Isolation and characterization of Golgi membranes from bovine liver. 424 7

The three Golgi fractions isolated from rat liver homogenates by the procedure given in the companion paper account for 6-7% of the protein of the total microsomal fraction used as starting preparation. The lightest, most homogeneous Golgi fraction (GF(1)) lacks typical "microsomal" activities, e.g., glucose-6-phosphatase, NADPH-cytochrome c-reductase, and cytochrome P-450. The heaviest, most heterogeneous fraction (GF(3)) is contaminated by endoplasmic reticulum membranes to the extent of approximately 15% of its protein. The three fractions taken together account for nearly all the UDP-galactose: N-acetyl-glucosamine galactosyltransferase of the parent microsomal fraction, and for approximately 70% of the activity of the original homogenate. Omission of the ethanol treatment of the animals reduces the recovery by half. The transferase activity is associated with the membranes of the Golgi elements, not with their content. Galactose is transferred not only to N-acetyl-glucosamine but also to an unidentified lipid-soluble component.
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PMID:Golgi fractions prepared from rat liver homogenates. II. Biochemical characterization. 435 72

Crude microsomes from porcine endometrium and three subfractions obtained by a modification of Rothschild's technique were characterized by RNA/protein ratio, marker enzyme activities and morphological appearance. The microsomes were devoid of glucose-6-phosphatase activity. They contained approximately 10% of arylesterase-, approximately 30% of both NADPH-cytochrome reductase- and UDPgalactose-N-acetyl-glucosamine beta-D-galactosyltransferase- and approximately 60% of 5'-nucleotidase activities present in the homogenates. Subfraction I (smooth membranes) had twice the galactosyltransferase activity of Subfraction II (smooth and rough membranes + free ribosomes); both subfractions were rich in 5'-nucleotidase and cytochrome reductase activities. Subfraction III (rough membranes) had very low marker activities but exhibited the highest RNA/protein ratio, which was lowest in I.
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PMID:Characterization of microsomal subfractions from porcine endometrium cells. 619 68

To study the relationship between the dose of phenobarbital (PB) and the magnitude of its effects on microsomal enzymes, cytochrome P-450, UDP-glucuronyl transferase (UDPGT), and glucose-6-phosphatase (G6P) activities were determined in liver homogenate and microsome preparations from control rats and rats treated for 6 days with PB at doses ranging from 1 to 125 mg/kg/day. Both P-450 and UDPGT activities were enhanced by PB in a dose-related fashion. However, while the lowest dose of the drug to produce significant induction of both enzymes was the same (3 mg/kg), maximal induction of P-450 (214%) and UDPGT (285%) was obtained with different doses of PB, namely 75 and 125 mg/kg, respectively. UDPGT induction could equally be demonstrated regardless of whether "native" enzyme or enzyme activated by UDP-N-acetyl glucosamine, digitonin or deoxycholate was employed. In contrast to these inducing effects of the drug on P-450 and UDPGT, PB treatment resulted in a dose-related inhibition of G6P activity. The inhibitory effect was observed with both "native" and deoxycholate-activated enzymes, and could be demonstrated whether the data were expressed as enzyme specific activity (nanomoles per minute per milligram microsomal protein) or as total G6P activity (micromoles per minute per 100 g body weight). These results indicate that: (I) enzyme induction by PB is dose-related; (ii) induction of both P-450 and UDPGT is obtained in the rat with doses of the drug similar to those given to man; and (iii) observed inhibition of G6P activity by PB does not solely reflect an enzymatic dilution secondary to the proliferated endoplasmic reticulum.
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PMID:Dose-related effects of phenobarbital on hepatic microsomal enzymes. 631 41

Plasma membranes have been isolated from chicken liver and from Mc-29 virus induced transplantable hepatoma. The purity of membrane preparations has been checked by electron microscopy and by determination of the activity of some enzymes: 5'-nucleotidase, Na+, K+-ATP-ase, Mg2+-ATP-ase, alkaline beta-glycerophosphatase and glucose-6-phosphatase. In hepatoma membranes the activity of 5'-nucleotidase, Na+, K+-ATP-ase and Mg2+-ATP-ase was lower, that of alkaline phosphatase higher, than in liver membrane preparation. The incorporation rate of glucosamine-14C into UDP-N-acetylglucosamine and into plasma membrane glucosamine have been studied as well. The rate of synthesis of UDP-N-acetylglucosamine was faster in liver than in tumor cells. The labeling of hepatoma plasma membranes with glucosamine-14C occurred more slowly than that of liver ones. The rate of transfer of N-acetylglucosamine from UDP-N-acetylglucosamine to membrane-bound glucosamine is lower in hepatoma, than in liver cells.
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PMID:Isolation and partial characterization of plasma membranes from chicken liver and from Mc-29 virus induced transplantable hepatoma. 745 56

Glucosamine, a potent inhibitor of glucokinase (hexokinase IV or D), was used to estimate the contribution of this enzyme to glucose phosphorylation in freshly isolated rat hepatocytes and its sensitivity to fructose 6-phosphate in situ. Experiments with radiolabelled glucosamine indicated that this amino sugar, at concentrations of 5 or 40 mM, readily penetrated hepatocytes to reach in 1 min a total (i.e., glucosamine+metabolites) intracellular concentration equal to 0.8-1.2-fold its extracellular concentration. In marked contrast, N-acetylglucosamine barely penetrated the cells. The detritiation of [2-3H]glucose, used to estimate glucose phosphorylation in intact cells, was inhibited by glucosamine much more potently than by N-acetylglucosamine, half-maximal effects being reached at about 2.5 and 30 mM respectively. Extrapolation of the data indicated that about 12% of the detritiation was resistant to glucosamine. Dihydroxyacetone (10 mM), lactate (10 mM) + pyruvate (1 mM), and glucagon (1 microM) increased up to 8-fold the concentration of hexose 6-phosphates (glucose 6-phosphate+fructose 6-phosphate) and, against expectations, modestly decreased the detritiation rate measured in the absence of glucosamine. In the presence of 40 mM glucosamine, these agents increased the detritiation rate, which then positively correlated with the concentration of hexose 6-phosphates. This hexose 6-phosphates-dependent detritiation was sensitive to inhibition by vanadate, and was also catalysed by gel-filtered cell-free extracts, as well as by liver microsomes in the presence of phosphoglucoisomerase; it can be explained by an exchange reaction catalysed by glucose-6-phosphatase. When this exchange reaction is taken into account, it appears that the rate of glucose detritiation attributable to glucokinase decreases when the concentration of hexose 6-phosphates increases. This is in agreement with the known effect of fructose 6-phosphate to potentiate the inhibition of glucokinase by its regulatory protein.
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PMID:Glucosamine-sensitive and -insensitive detritiation of [2-3H]glucose in isolated rat hepatocytes: a study of the contributions of glucokinase and glucose-6-phosphatase. 775 69

With the aim of questioning the apparent loss of specificity of the microsomal glucose-6-phosphate phosphohydrolase after detergent-treatment, we performed competitive inhibition experiments among the four best substrates of the enzyme, i.e. the 6-phosphates of glucose (Glc6P), mannose-6 (Man6P), glucosamine (GlcN6P) and 2-deoxyglucose (dGlc6P). The Km and Vmax of glucose-6-phosphatase (Glc6Pase) and mannose-6-phosphatase (Man6Pase), assayed either by complex formation determination of P(i) produced or by radiometric determination of [U-14C]Glc or [U-14C]Man, were very close to 1 mM and 0.64 mumol.min-1.mg-1 microsomal protein, respectively. The Km of the enzyme for GlcN6P and for dGlc6P, determined by colorimetric assay of P(i), were equal to 1.53 +/- 0.07 mM and 2.35 +/- 0.15 mM, respectively, whilst the Vmax was not different from that of Glc6Pase and Man6Pase. Unexpectedly, the Ki of Man6P (1.61 +/- 0.22 mM), GlcN6P (2.24 +/- 0.17 mM) and dGlc6P (3.40 +/- 0.07 mM) for Glc6Pase, assayed by liberation of [U-14C]Glc, were significantly (50%) higher than their Km previously determined. The Ki of Glc6P (0.66 +/- 0.05 mM) for Man6Pase, assayed by liberation of [U-14C]Man, was significantly lower than its Km previously determined. In contrast, the Ki of GlcN6P (1.55 +/- 0.05 mM) for Man6Pase, assayed by the radiometric assay, was not different from its Km previously determined. It can be inferred from these data that Glc6P phosphohydrolase exhibits specific behaviour towards Glc6P after the detergent-treatment of the microsomal membrane.
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PMID:Glucose-6-phosphate phosphohydrolase of detergent-treated liver microsomal membranes exhibits a specific kinetic behaviour towards glucose 6-phosphate. 838 45

Hepatic gene expression of P-enolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (Glc-6-Pase) is regulated in response to changes in the availability of substrates, in particular glucose (Glc; Massillon, D., Barzilai, N., Chen, W., Hu, M., and Rossetti, L. (1996) J. Biol. Chem. 271, 9871-9874). We investigated the mechanism(s) in conscious rats. Hyperglycemia per se caused a rapid and marked increase in Glc-6-Pase mRNA abundance and protein levels. By contrast, hyperglycemia decreased the abundance of PEPCK mRNA. Importantly, inhibition of glucokinase activity by glucosamine infusion blunted both the stimulation of Glc-6-Pase and the inhibition of PEPCK gene expression by Glc, suggesting that an intrahepatic signal (metabolite) generated by the metabolism of glucose at or beyond Glc-6-P was responsible for the regulatory effect of Glc. The effect of Glc on the L-type pyruvate kinase gene is mediated by xylulose-5-P (Doiron, B., Cuif, M., Chen, R., and Kahn, A. (1996) J. Biol. Chem. 271, 5321-5324). Thus, we next investigated whether an isolated increase in the hepatic concentration of this metabolite can also reproduce the effects of Glc on Glc-6-Pase and PEPCK gene expression in vivo. Xylitol, which is directly converted to xylulose-5-P in the liver, was infused to raise the hepatic concentration of xylulose-5-P by approximately 3-fold. Xylitol infusion did not alter the levels of Glc-6-P and of fructose-2,6-biphosphate. However, it replicated the effects of hyperglycemia on Glc-6-Pase and PEPCK gene expression and resulted in a 75% increase in the in vivo flux through Glc-6-Pase (total glucose output).
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PMID:Carbon flux via the pentose phosphate pathway regulates the hepatic expression of the glucose-6-phosphatase and phosphoenolpyruvate carboxykinase genes in conscious rats. 941 69


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