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)

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

In order to study the characteristics of the intracellular Ca store of mast cells, organelles of rat peritoneal mast cells were fractionated. The binding of 45Ca was at its peak in the fractions where the highest activity of glucose-6-phosphatase, the marker enzyme for the endoplasmic reticulum (ER), was measured. The ER-rich fraction exhibited an ATP-dependent uptake of 45Ca and this uptake was inhibited by pretreatment with ATPase inhibitors such as LaCl3 or Na3VO4. When inositol 1,4,5-trisphosphate (IP3) was added to a medium containing the 45Ca-loaded ER fraction, it caused a dose-dependent release of 45Ca at concentrations higher than 0.5 microM, while inositol 1-monophosphate and inositol 1,4-bisphosphate were not effective even at higher concentrations. The results of a binding assay using 3H-labeled IP3 indicated that there exist two kinds of IP3 binding site in the ER: one is of high affinity but low capacity while the other is of low affinity and high capacity. IP3-induced 45Ca release was dose-dependently inhibited by pretreatment with c-AMP. The present study supports the assumption that the intracellular Ca store associated with histamine release from the mast cell is the ER.
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PMID:Ca uptake and Ca releasing properties of the endoplasmic reticulum in rat peritoneal mast cells. 246 54

In order to find the markers of the toxicity of the autoxidized lipids in the liver, rats were given a lethal amount of secondary autoxidation products of linoleic acid (400 mg/rat/day for 3 days) and then changes in the hepatic metabolic functions were analyzed. A decrease in acetyl-CoA level to half caused by the depletion of CoASH was reported in an associated paper (J. Nutr. Sci. Vitaminol., 35, 11-23, 1989). Citrate, isocitrate, and 2-oxoglutarate also decreased to half the level of those of the control group. Reduction in isocitrate dehydrogenase activity was only 25%, while NADH2 and ATP levels remained unchanged. Thus, the reduction in the citrate cycle activity was due to the decrease in acetyl-CoA. The activity of mitochondrial succinate dehydrogenase was decreased to 1/5. Other appreciable changes were depletion of glucose 6-phosphate and fructose 6-phosphate, accumulation of glucose 1-phosphate, reductions in hexokinase, phosphofructokinase, glucose-6-phosphatase, phosphoglucomutase, and phosphogluconate dehydrogenase activities, and decrease in the NADPH2 level. It was considered that these changes were caused by the depletion of glucose 6-phosphate whose synthetic pathways were abnormal. Therefore, the markers of the hepatotoxicity of secondary products were the changes in the CoASH level and the activities of succinate dehydrogenase and synthetic pathways for glucose 6-phosphate.
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PMID:Succinate dehydrogenase and synthetic pathways of glucose 6-phosphate are also the markers of the toxicity of orally administered secondary autoxidation products of linoleic acid in rat liver. 254 8

Inclusion bodies containing glycogen-enzymes were found in 30 to 60% of type 2 fibres of tenotomized calf muscles (m. gastrocnemius, m. soleus, m. plantaris) in rats, using histochemical reactions. The bodies appeared within 1 week after the tenotomy and were localized both in the central and the subsarcolemmal regions and rarely extruded into the extracellular space. These aggregates are 3 to 15 microns in length and 2 to 11 microns in diameter. In addition to glycogen, these bodies also contained various enzymes of the glycogen metabolism such as phosphorylase, a branching enzyme, and glucose-6-phosphatase, but showed no NADH-reductase, lactate dehydrogenase, or myofibrillar ATP-ase activity. The results indicate that glycogen-enzymes containing bodies are a degenerative phenomenon, which occurs only in type 2 fibres of the tenotomized muscles.
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PMID:Glycogen-enzymes containing bodies in type 2 fibres of tenotomized muscles in the rat. 255 27

Histochemical methods were used to study the localization and activity of acid and alkaline phosphatases, ATP-ase, 5-nucleotidase, and glucose-6-phosphatase in tissues of the mature form of Hymenolepis nana. Considerable differences in activity and localization of particular enzymes were observed in the organs of the parasite. The results obtained permit the statement that the integument is the most active enzymatically; in connection with the literature data, this gives grounds for the thesis that the integument of the cestodes functions as an absorbent-digestive organ.
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PMID:The activity of some phosphatases in tissues of adult Hymenolepis nana Siebold (Csetoda). 255 20

In this paper we show that hepatocytes that have been depleted of K+ secrete albumin, alpha-1-anti-trypsin and transferrin at a slower rate than cells to which K+ has been returned. K+ depletion has no effect on the intracellular nucleotide pools, and we provide evidence that the inhibitions of secretion caused by depletion of K+ and depletion of ATP are independent. Studies of the processing of alpha-1-anti-trypsin show that K+ depletion inhibits the formation of the mature form of the protein, but that immature forms are never secreted. In cells to which K+ was returned, secretion of the mature form was restored. This implies that transport is blocked at a point before the proteins reach the processing enzymes. Proteins delayed by K+ depletion are not removed from the secretory pathway, but are free to mix with protein synthesized subsequently. These data are supported by subcellular fractionation experiments, which show that the secretory proteins are delayed before reaching the Golgi complex, and by immunoelectron microscopic studies. These show that in K+-deficient cells the morphology of both the endoplasmic reticulum and the Golgi complex is normal. The secretory proteins are trapped in smooth vesicles that contain reaction product when incubated for glucose-6-phosphatase, a marker for the endoplasmic reticulum.
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PMID:Potassium depletion inhibits the intracellular transport of secretory proteins between the endoplasmic reticulum and the Golgi complex. 278 29

Glucose and lipid metabolism in the brain, liver and in a transplanted tumour were found to be variously altered within 2 to 3 h of administering single doses of the radiosensitizer Ro-03-8799 to normal and tumour-bearing mice. Hepatic lactate and glycerol-3-phosphate (G3P) levels were decreased but those of the ketone body beta-hydroxybutyrate (beta-HOBu) were raised. However, in the tumour, these levels were all enhanced. The lactate levels in brain remained relatively constant but both beta-HOBu and G3P levels were altered in a manner similar to that in the liver. The levels of glucose were approximately doubled in blood, brain and tumour, but whereas tumour G6P levels increased, those in the brain were lowered to below the limits of detection. Hepatic glucose levels were significantly decreased after 1 h but G6P levels were not affected. These changes could neither be related to inhibitory effects on hepatic glucokinase or brain hexokinase activity nor to limiting amounts of ATP in both tissues. However, the activity of glucose-6-phosphatase (G6P'ase) was distinctly raised in the liver and the hepatic glycogen stores were also rapidly lowered. Overall, the results suggest that Ro-03-8799 exerts a stimulatory effect on glucose production in the liver. In both liver and brain the levels of free fatty acids and phospholipids were increased whereas those of esterified fatty acids were lowered. Most importantly, the changes in metabolite levels affect the cellular redox couples; those of the cytosol (lactate/pyruvate; G3P/dihydroxyacetone phosphate (DAP] are directed towards the oxidised state in the liver but to a more reduced state in the tumour. The mitochondrial couple (beta-HOBu/acetoacetate (AcAc)) in both tissues is shifted towards the reduced state. These metabolic changes may result in an increase in the degree of hypoxia in the tumour and may well play an important role in the development of neuropathies.
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PMID:Effects on intermediary metabolism in mouse tissues by Ro-03-8799. 282 72

The distribution of hepatic binding sites for the calcium-mobilizing second messenger, inositol 1,4,5-trisphosphate (IP3), was analyzed in subcellular fractions of the rat liver by binding studies with [32P]IP3 and compared with the Ca2+ release elicited by IP3 in each fraction. Three major subcellular fractions enriched in plasma membrane, mitochondria, and endoplasmic reticulum were characterized for their 5'-nucleotidase, glucose-6-phosphatase, succinate reductase, and angiotensin II binding activities. The fraction enriched in plasma membrane showed 7- and 20-fold increases in IP3 binding capacity over those enriched in endoplasmic reticulum and mitochondria, respectively, and contained a single class of high-affinity binding sites with Kd of 1.7 +/- 1.0 nM and concentration of 239 +/- 91 fmol/mg protein. IP3 binding reached equilibrium in 30 min at 0 degrees C, and the half-time of dissociation was about 15 min. The specificity of the IP3 binding sites was indicated by their markedly lower affinities for inositol 1-phosphate, phytic acid, fructose 1,6-bisphosphate, 2,3-bisphosphoglycerate, and inositol 1,3,4,5-tetrakisphosphate. The Ca2+-releasing activity of IP3 in the subcellular fractions was monitored with the fluorescent indicator, Fura-2. All three fractions showed ATP-dependent Ca2+ uptake and rapidly released Ca2+ in response in IP3. The fraction enriched in plasma membrane was the most active in this regard, releasing 174 +/- 67 pmol Ca2+/mg of protein compared to 45 +/- 10 and 48 +/- 7 pmol/mg protein for the fractions enriched in endoplasmic reticulum and mitochondria, respectively. These data suggest that the [32P]IP3 binding sites represent specific intracellular receptors through which IP3 mobilizes Ca2+ from a storage site associated (or co-purifying) with the plasma membrane of the rat liver. It is likely that a specialized vesicular system (to which IP3 can bind and trigger the release of Ca2+) is located in close proximity with the plasma membrane and is thus adjacent to the site at which IP3 is produced during stimulation of the hepatocyte by Ca2+-mobilizing hormones.
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PMID:Characterization of inositol 1,4,5-trisphosphate receptors and calcium mobilization in a hepatic plasma membrane fraction. 283 98

We present a method to determine glucose 6-phosphate activity. This assay measures the rate of glucose released in the glucose-6-phosphatase reaction. The glucose is oxidized to beta-D-gluconolactone by glucose dehydrogenase in a coupled reaction that uses NAD(P)+. The determination is rapid, reproducible, and does not require withdrawal, precipitation, centrifugation, or neutralization steps. This method provides a simple resolution to the problem of the nonspecific appearance of Pi, which is especially important in studies of regulation of glucose-6-phosphatase performed in the presence of ATP.
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PMID:Determination of glucose-6-phosphatase activity using the glucose dehydrogenase-coupled reaction. 284 88

Studies were performed to determine whether hypoglycemia or the glucagon response to hypoglycemia increases uric acid production in glycogen storage disease type I (glucose-6-phosphatase deficiency). Three adults with this disease had hyperuricemia (serum urate, 11.3-12.4 mg/dl) and reduced renal clearance of urate (renal urate clearance, 1.1-3.1 ml/min). These abnormalities were improved in one patient by intravenous glucose infusion for 1 mo, suggesting a role for hypoglycemia and its attendant effects on urate metabolism and excretion. A pharmacologic dose of glucagon caused a rise in serum urate from 11.4 to 13.0 mg/dl, a ninefold increase in urinary excretion of oxypurines, a 65% increase in urinary radioactivity derived from radioactively labeled adenine nucleotides, and a 90% increase in urinary uric acid excretion. These changes indicate that intravenous glucagon increases ATP breakdown to its degradation products and thereby stimulates uric acid production. To observe whether physiologic changes in serum glucagon modulate ATP degradation, uric acid production was compared during saline and somatostatin infusions. Serum urate, urinary oxypurine, radioactivity, and uric acid excretion increased during saline infusion as patients became hypoglycemic. Infusion of somatostatin suppressed these increases despite hypoglycemia and decreased the elevated plasma glucagon levels from a mean of 81.3 to 52.2 pg/ml. These data suggest that hypoglycemia can stimulate uric acid synthesis in glucose-6-phosphatase deficiency. Glucagon contributes to this response by activating ATP degradation to uric acid.
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PMID:Hyperuricemia in glycogen storage disease type I. Contributions by hypoglycemia and hyperglucagonemia to increased urate production. 285 25


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