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)

Oral administration of embelin (75 mg/kg per day, daily for 15 and 30 days) to male rats caused significant elevation in the uptake of D-glucose, L-alanine, L-leucine and calcium in small intestinal segments. Embelin also produced significant increases in intestinal brush border membrane-associated enzymes (sucrase, lactase, maltase, alkaline phosphatase and leucine aminopeptidase) in both intestinal homogenates and partially purified brush border membrane preparations. Significant increases were also noted for microsomal glucose-6-phosphatase and cytosolic lactate dehydrogenase. Increase in brush border membrane-associated total lipids, phospholipids, cholesterol, triacylglycerol, unesterified fatty acids and ganglioside sialic acid were seen but not in the cholesterol/phospholipid molar ratio. All these changes returned to control or near control levels following withdrawal of the drug.
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PMID:Effects of embelin, a male antifertility agent, on absorptive and digestive functions of rat intestine. 192 15

Administration of Embelin, an experimental antifertility agent, to male rats (20 mg/kg body wt/day, daily for 15 and 30 days), caused an elevation in the uptake of D-glucose, L-alanine, L-leucine, and calcium in the small intestinal segments. An increase was also noted in the intestinal brush border membrane (BBM)-associated enzymes, sucrase, lactase, maltase, alkaline phosphatase, and leucine aminopeptidase in both the intestinal homogenates and partially purified BBM preparations, particularly after 30-day administration of the drug. Embelin treatment also caused a significant increase in the microsomal glucose-6-phosphatase and the cytosolic enzyme, lactate dehydrogenase. In the Embelin-treated animals BBM-associated total lipids, phospholipids, cholesterol, triacylglycerol, unesterified fatty acids, ganglioside-sialic acids as well as the cholesterol/phospholipids molar ratio showed a considerable increase. All these changes in the Embelin-treated animals were restored back to the normal or near normal biochemical makeup when the drug therapy was withdrawn and the animals were allowed to recover for another 15 and 30 days, respectively.
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PMID:Changes in glucose/amino acid/calcium uptake and brush-border membrane-associated enzymes in rat small intestine after the administration of embelin (plant benzoquinone), an antifertility agent. 211 47

It has recently been reported that free Ca2+, a second hormonal messenger in the liver, can modulate the activity of liver glucose-6-phosphatase by inhibition (van de Werve, G. (1989) J. Biol. Chem. 264, 6033-6036) or activation (Yamagushi, M., Mori, S., and Suketa, Y. (1989) Chem. Pharm. Bull. (Tokyo) 37, 388-390). Such a controversial role for Ca2+ is reinvestigated by comparing the effect of the addition of free Ca2+ (10(-10) to 20.10(-3) M) under the form of CaCl2 or of Ca-EGTA buffers. We show that the glucose-6-phosphatase activity is: 1) increased in the presence of CaCl2 at concentrations higher than 10(-4) M and unaffected in the presence of CaCl2 at lower concentrations; 2) decreased in the presence of Ca-EGTA buffers yielding free Ca2+ concentrations higher than 10(-8) M; 3) the latter effect is not depending on free Ca2+ or free EGTA concentrations, but on Ca.EGTA complex concentration. In addition, these effects can be reproduced in the same concentration ranges by MgCl2 and Mg-EDTA buffers, respectively. It is concluded that a physiological role for free Ca2+ on the activity of liver glucose-6-phosphatase remains to be established.
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PMID:Reappraisal of the effect of Ca2+ on the activity of liver microsomal glucose-6-phosphatase. 215 96

The effects of Ca2+ on the microsomal glucose-6-phosphatase activity were investigated. Evidence is provided that increases by Ca2+ in both the pyrophosphatase and the glucose-6-phosphate-hydrolysing activities are due to an increase in microsomal transport capacity of T2, the phosphate/pyrophosphate-transport protein.
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PMID:Calcium activates glucose-6-phosphatase in intact rat hepatic microsomes. 217 54

It was known in the 1950s that hepatic microsomal glucose-6-phosphatase plays an important role in the regulation of blood glucose levels. All attempts since then to purify a single polypeptide with glucose-6-phosphatase activity have failed. Until recently, virtually nothing was known about the molecular basis of glucose-6-phosphatase or its regulation. Recent studies of the type 1 glycogen storage diseases, which are human genetic deficiencies that result in impaired glucose-6-phosphatase activity, have greatly increased our understanding of glucose-6-phosphatase. Glucose-6-phosphatase has been shown to comprise at least five different polypeptides, the catalytic subunit of glucose-6-phosphatase with its active site situated in the lumen of the endoplasmic reticulum; a regulatory Ca2+ binding protein; and three transport proteins, T1, T2, and T3, which respectively allow glucose-6-phosphate, phosphate, and glucose to cross the endoplasmic reticulum membrane. Purified glucose-6-phosphatase proteins, immunospecific antibodies, and improved assay techniques have led to the diagnosis of a variety of new type 1 glycogen storage diseases. Recent studies of the type 1 glycogen storage diseases have led to a much greater understanding of the role and regulation of each of the glucose-6-phosphatase proteins.
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PMID:Molecular pathology of glucose-6-phosphatase. 216 25

We have recently shown that the Ca.EGTA and Mg.EDTA complexes, but not free Ca2+ or Mg2+, inhibit the liver glucose-6-phosphatase (Mithieux, G., Vega, F. V., Beylot, M., and Riou, J. P. (1990) J. Biol. Chem. 265, 7257-7259). In this work, we report that, when complexed with Mg2+, two endogenous dicarboxylic keto acids (alpha-ketoglutarate (alpha-KG) and oxaloacetate (OAA] inhibit the glucose-6-phosphatase activity at low concentrations of substrate. This phenomenon is specific for complexes of Mg2+ with alpha-KG and OAA since 1) the complexes of Mg2+ with a number of other di- or tricarboxylic acids having high structural analogy with alpha-KG and OAA (oxalate, malate, succinate, citrate, aspartate, and glutamate) do not inhibit the glucose-6-phosphatase activity and 2) the Ca.alpha-KG and Ca.OAA chelates do not inhibit the glucose-6-phosphatase activity. In the presence of Mg.alpha-KG or Mg.OAA chelates, the enzyme displays sigmoid kinetics; the Hanes plots deviate from linearity, indicating the positive cooperative dependence of the velocity upon the substrate concentration. Hill coefficients (equal to 1 in the absence of the chelates) of 1.23 and 1.33 have been determined in the presence of Mg.alpha-KG and Mg.OAA complexes, respectively. The disruption of microsomal integrity by detergents abolishes the effect of Mg.alpha-KG and Mg.OAA, suggesting that the magnesium chelates inhibit the translocase component of the glucose-6-phosphatase system.
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PMID:The liver glucose-6-phosphatase of intact microsomes is inhibited and displays sigmoid kinetics in the presence of alpha-ketoglutarate-magnesium and oxaloacetate-magnesium chelates. 217 3

Carbon tetrachloride (CCl4) brings about a rise in cytosolic free calcium which may lead to glycogen mobilization. Therefore, glycogen and glucose-6-phosphatase (G-6-pase) levels in the liver of parathyroidectomized (PTX) rats following CCl4 treatment have been estimated. CCl4 depletes both glycogen and G-6-pase levels in the liver. PTX followed by CCl4 administration, however, fails to restore liver glycogen and G-6-pase levels. The results suggest that neither cytosolic Ca2+ nor phospholipase A2 mediation is needed for glycogen mobilization, however, glucocorticoid intervention might have a role in such mechanisms.
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PMID:Influence of parathyroidectomy on liver glycogen in rats treated with carbon tetrachloride. 225 76

(1) The features of MgATP-dependent Ca2+ accumulation under stimulation with glucose 6-phosphate were studied in rat kidney microsomes. (2) Ca2+ accumulated in the presence of MgATP alone does not exceed approx. 2 nmol/mg protein. (3) Glucose 6-phosphate markedly stimulates Ca2+ accumulation, up to steady-state levels approx. 15-fold higher than in its absence. (4) The hydrolysis of glucose 6-phosphate by glucose-6-phosphatase is essential for the stimulation, as shown by inhibiting the glucose 6-phosphate hydrolysis with adequate concentrations of vanadate. Inorganic phosphate is accumulated in microsomal vesicles during glucose 6-phosphate-stimulated Ca2+ uptake in equimolar amounts with respects to Ca2+. (5) Increasing concentrations of glucose 6-phosphate result in increasing stimulations of Ca2+ uptake, until a maximal Ca2(+)-loading capacity of approx. 27 nmol/mg microsomal protein is reached. It is suggested that the enlargement of the kidney microsomal Ca2+ pool induced by glucose 6-phosphate (an important metabolite in kidney) might play a role in the regulation of Ca2+ homeostasis in kidney tubular cells.
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PMID:Glucose 6-phosphate stimulation of MgATP-dependent Ca2+ uptake by rat kidney microsomes. 230 99

Inositol 1,4,5-trisphosphate [Ins(1,4,5)P3], arising from hydrolysis of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2], is proposed as the link between membrane-receptor activation and mobilization of Ca2+ from intracellular sites in hormone-secreting cells. The location of Ins(1,4,5)P3-sensitive membranes was investigated in cultured neonatal beta-cells. Membranes were obtained after lysis of cells attached to positively charged Sephadex. After lysis the presence of the enzyme markers 5'-nucleotidase, glucose-6-phosphatase, NADH-cytochrome c reductase, UDP-galactosyltransferase and succinate dehydrogenase indicated the mixed nature of the preparation. After sonication, however, UDP-galactosyltransferase and succinate dehydrogenase activities were undetectable, but 4.8% of total cellular glucose-6-phosphatase and 3.4% of total cellular NADH-cytochrome c reductase remained with 5'-nucleotidase in the preparation, indicating endoplasmic-reticulum association. ATP-dependent 45Ca2+ accumulation was shown in this preparation (410 +/- 24 pmol/mg of protein at 150 nM free Ca2+) and was inhibited by vanadate (100 microM). Ca2+ release was effected by Ins(1,4,5)P3, with half-maximal release at 0.5 +/- 0.14 microM-Ins(1,4,5)P3, t1/2 11.2 +/- 1.1 s. GTP- and guanosine 5'-[beta gamma-imido]triphosphate (p[NH]ppG)-promoted release of 45Ca2+ was demonstrated in this preparation, but the kinetics of release (half-maximal Ca2+ release at 5.4 +/- 0.7 microM, with t1/2 77.3 +/- 6.9 s, and at 51.1 +/- 4.2 microM, with t1/2 19.0 +/- 2.2 s, for GTP and p[NH]ppG respectively), and the ability of neomycin sulphate to block p[NH]ppG-induced release only, are indicative of separate release mechanisms after treatment with these agents. A close association between plasma membrane and elements of the endoplasmic reticulum is indicated in this model, providing a possible mechanism for local alterations in free Ca2+ in the sub-plasma-membrane region.
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PMID:GTP- and inositol 1,4,5-trisphosphate-induced release of 45Ca2+ from a membrane store co-localized with pancreatic-islet-cell plasma membrane. 245 19

The glucose analogue 1-deoxynojirimycin (dNOJ) and some of its N-substituted derivatives have recently been described as potent inhibitors of the hepatic glycogenolysis induced by glucagon, Ca2+ ionophores or anoxia. The inhibition increased with time, in spite of a persistently high level of phosphorylase a [Bollen, M., Vandebroeck, A. & Stalmans, W. (1988) Biochem. Pharmacol. 37, 905-909]. dNOJ equilibrates within 1 min across the plasma membrane of hepatocytes. It is not phosphorylated or oxidized in the cell. The observation that dNOJ did not affect gluconeogenesis excludes the possibility that glucose-6-phosphatase is the target for the inhibition of glucose production from glycogen. Neither were the catalytic activities of phosphoglucomutase and phosphorylase a affected by the compound. dNOJ and two N-substituted derivatives inhibited instantaneously and completely the alpha-1,6-glucosidase activity of the debranching enzyme, with I50 values in the mumolar range. In contrast, the glucanotransferase activity of the latter enzyme was not inhibited by the compounds at 0.2 mM. The effect of dNOJ was further studied in an in vitro model system of glycogenolysis. The results were compatible with a block of glycogenolysis at the time when phosphorylase has removed the available glucosyl residues from the outer chains of the glycogen particles. This mechanism appears to account for the lag in the response of glycogenolysis to dNOJ.
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PMID:The antiglycogenolytic action of 1-deoxynojirimycin results from a specific inhibition of the alpha-1,6-glucosidase activity of the debranching enzyme. 252 91


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