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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)

Carbamyl phosphate : glucose phosphotransferase and glucose-6-phosphate (Glc-6-P) phosphohydrolase activities have beeh demonstrated in pancreas, adrenals, brain, testes, spleen, and lung. Catalysis of these activities by classical multifunctional glucose-6-phosphatase (D-glucose-6-phosphate phosphohydrolase; EC 3.1.3.9) has been firmly established for the first four of these tissues on the basis of characteristic catalytic properties of the transferase pH-activity profiles, apparent Km values for carbamyl phosphate and glucose, substrate specificity, susceptibility to inhibition by molybdate, and activation by deoxycholate. Additional such activity due to non-specific acid (and alkaline) phosphatase action also is indicated at very high glucose concentrations. The possible physiological significance of the newly-elucidated presence of glucose-6-phosphatase-phosphotransferase in these various tissues, in addition to previously extensively studied liver, kidney, and mucosa of small intestine, is discussed briefly.
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PMID:Mammalian carbamyl phosphate : glucose phosphotransferase and glucose-6-phosphate phosphohydrolase: extended tissue distribution. 16 20

DNA-, RNA-, and lipidsynthesis, glucose-6-phosphate-dehydrogenase, glucose-6-phosphatase and succinate-dehydrogenase were studied in the different morphologic stages of blood schizogony of Plasmodium vinckei. For the separation of these stages of the maturation cycle a discontinuous Ficoll-density gradient was developed. By this method the morphologic stages were separated and obtained in sufficient amounts. DNA-, RNA- and lipidsynthesis was not continuous in the intraerythrocytic cycle of the parasite. The glucose-6-phosphate dehydrogenase activity of the infected erythrocytes decreases whereas that of the glucose-6-phosphatase increases in the maturation cycle of P. vinckei.
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PMID:[DNA-, RNA-, lipidsynthesis and the specific activity of the glucose-6-phosphate dehydrogenase and glucose-6-phosphatase in the different morphologic stages of Plasmodium vinckei]. 16 81

The activities of liver microsomal enzymes were studied in preparations from unanesthetized rats and rats anesthetized for one hour with nitrous oxide, diethyl ether, halothane or chloroform. Most of the enzymes studied were cytochrome P-450-dependent oxygenases that hydroxylate endogenous substrates. The other microsomal enzymes, assayed for comparison, included the cytochrome P-450-dependent aminopyrine demethylase, glucose-6-phosphatase, a dehydrogenase, and NADPH-cytochrome P-450 reductase. No anesthetic was associated with a significant change in activity of any enzyme studied. In rats pretreated with phenobarbital no anesthetic except chloroform changed enzymic activity. All hydroxylations were inhibited markedly by chloroform, as were a microsomal dehydrogenation, hydrolysis of glucose-6-phosphate, and NADPH-cytochrome P-450 reductase activity. Administration of alpha-tocopherol did not prevent the inhibition associated with chloroform in phenobarbital-induced animals. It is concluded that cytochrome P-450-dependent hydroxylations involved in metabolic processes normally proceeding in the endoplasmic reticulum of the liver are not permanently affected by the anesthetics used in this study. The inhibitory effect of chloroform after pretreatment with phenobarbital is unspecific and affects a large number of different microsomal enzymes. Evidence that mechanisms other than lipid peroxidation may be responsible for the toxic effects of chloroform in the liver is presented.
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PMID:Inhalation anesthetics and cytochrome P-450-dependent reactions in rat liver microsomes. 16 17

The effect of gamma irradiation on alkaline phosphatase and glucose-6-phosphate has been studied in three anatomically different regions of the small intestine at a surface dose of 400 R. Both the enzymatic activities were shown to be enhanced in duodenum, jejunum and ileum 24 hours after irradiation. The activity of alkaline phosphatase on day 3 tendeed to be low as compared to day 1 post irradiation, but glucose-6-phosphatase continued to rise even after day 3. Maximum rise of glucose-6-phosphatase was observed in the jejunum. On day 9, alkaline phosphatase was diminished below the controls in the whole of intestine, but appeared to be normal on day 10. Glucose-6-phosphatase in duodenum and jejunum on the other hand was comparable to that of control mice; but in ileum, the activity of this enzyme was below the normal values. Physiological significances of these enzymes in intestine has been discussed.
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PMID:Radiation effects on alkaline phosphatase and glucose-6-phosphatase in anatomically different regions of mouse intestine. 17 4

Inhibition by saccharin of rat liver glucose-6-phosphatase (EC 3.1.3.9) generally decreased as the pH increased in the range pH 4-8. This pattern was exhibited by homogenates from control and alloxan-treated animals assayed each in the absence and presence of 0.2% (w/v) deoxycholate. Saccharin inhibited in competitive fashion with respect to glucose-6-phosphate (glucose-6-P). There was a small increase in Km (glucose-6-P) but not K1 (saccharin) values in alloxan-treated rats when assays were conducted in the absence of deoxycholate. In the presence of this detergent there was no significant difference in these kinetic parameters between the alloxan-treated and control groups. Deoxycholate decreased Km (glucose-6-P) and increased K1 (saccharin) values. Calculations using these kinetic parameters indicate that, under usual hepatic glucose-6-P concentrations and relatively high levels of saccharin in liver, the inhibition by saccharin of glucose-6-phosphatase is unlikely to be of major significance in vivo.
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PMID:Inhibition by saccharin of glucose-6-phosphatase: effects of alloxan in vivo and deoxycholate in vitro. 17 81

The histochemical detection of glucose-6-phosphatase (G-6-Pase) in neurons of the CNS has been confirmed at the level of electron microscope. Both glucose-6-phosphate (G-6-P) and alpha-glycerophosphate (alpha-gP) can be used as substrates to localize the reaction product of this enzyme, which we have found in all cell types of the cerebral cortex, cerebellum and brain stem. The reaction was most prominent in large neurons, such as the Purkinje cells of the cerebellum and the pyramidal cells of the cerebral cortex. This is due to their extensive content of rough and smooth endoplasmic reticulum, the ultrastructural sites of G-6-Pase activity. It was possible to measure quantitatively the hydrolysis of G-6-P and alpha-gP in brain homogenates and also in microsomal fractions, the biochemical correlate of the cytochemically demonstrable activity. These results call for a reappraisal of the previous biochemical evidence, which negates the existence of brain G-6-Pase, and consequently a reassessment of current concepts pertaining to the metabolic regulation of brain glucose.
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PMID:Cytochemical localization of glucose-6-phosphatase activity in the central nervous system of the rat. 18 19

Iodoacetamide, N-ethylmaleimide, p-hydroxymercuribenzoate (p-MB) and HgCl2 were tested as inhibitors of microsomal glucose-6-phosphatase. Iodoacetamide had no effect at 2 mM. N-ethylmaleimide inhibited only crude, but not purified microsomal preparations (M2) or crude microsomes exposed to deoxycholate. 14C-labelled N-ethylmaleimide was not bound by the M2 protein fraction. p-MB inhibited all types of preparations and the inhibition was not counteracted by detergent. A more detailed study was carried out with the purified M2 fraction (specific activity: 2-4 mumoles Pi/min/mg protein). Glucose-6-phosphate hydrolysis was inhibited 50% by 5 X 10(-5) M p-MB. The inhibition was completely reversible by dithiothreitol except when the enzyme was pre-incubated with p-MB in the absence of substrate. Then p-MB accelerated the temperature-dependent inactivation of glucose-6-phosphatase. Binding studies showed that around 3 mumoles 14C-p-MB were incorporated into 100 mg M2 protein regardless of the concentration of mercurial in the incubation mixture. That is, over a 25 fold range of p-MB concentration, causing up to 80% inhibition of enzyme activity, no difference was seen in the amount of labelled p-MB which was irreversibly bound to M2 protein. Kinetically p-MB behaved like a reversible inhibitor and this was confirmed by dilution experiments. Several compounds, including some amino acids, antagonized the inhibition by p-MB. The order of effectiveness was EDTA greater than barbital greater than tryptophan greater than histidine greater than lysine greater than other amino acids. Glycine, Tris and urea were ineffective competitors of p-MB inhibition. Double reciprocal plots showed that the Km for glucose-6-phosphate was increased and the Vmax reduced in the presence of p-MB. HgCl2 was a more effective inhibitor than p-MB with a Ki of 6 X 10(-6) M. We conclude that a reaction of p-MB with M2 sulfhydryls does not play a part in the inhibition of enzyme activity. It is suggested that p-MB may interact with one or more amino acid side chains in such a way that enzyme conformation is altered.
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PMID:The effect of p-hydroxymercuribenzoate and congeners on microsomal glucose-6-phosphatase. 18 75

Activities of a broad spectrum of enzymes were studied histochemically in renal adenocarcinomas induced in young male F344 rats by chronic dietary administration of the carcinogen N(4'-fluoro-4-biphenylyl)acetamide. Enzymes included were: dehydrogenases of glucose-6-phosphate, lactate, succinate, malate, and alpha-glycerophosphate; peroxidase (catalase); glucose-6-phosphatase; alkaline and acid phosphatase; Mg2+ ATPase; 5'-nucleotidase; and aminopeptidase. Levels of enzyme activity were estimated visually and scored from 0 (not detectable) to a maximum of 5 (intense). Comparison of estimated activity for each enzyme was made between small neoplastic nodules (stage III tumors) and large adenocarcinomas (stage IV tumors) and between tumors and portions of normal proximal tubules in parenchyma of kidneys from untreated control rats. The results, which revealed nearly identical levels of activity for most enzymes in both stages III and IV tumors, suggested similar metabolic and biologic behavior of these lesions. However, when data for tumors were compared with data for normal proximal tubules, striking differences were observed consistent with: 1) a marked shift of energy metabolism from oxidative to glycolytic production of ATP, with a corresponding reduction in mitochondrial respiration; and 2) simplification of plasma membrane specializations that were possibly associated with a reduction or loss of transport function. These findings were compared with other histochemical, biochemical, and ultrastructural studies of renal adenocarcinomas in rats and man.
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PMID:Adenocarcinoma of the kidney. II. Enzyme histochemistry of renal adenocarcinomas induced in rats by N-(4'-fluoro-4-biphenylyl)acetamide. 18 77

The activity of hexokinase, glucose-6-phosphatase and glucose-6-phosphoric dehydrogenase was studied in the liver of rats after one hour, one and five days after a single oral administration of organic phosphorus insecticide valekson. It was determined that administration of the preparation led to an increase of activity in the homogenate and solubilization of glucose-6-phosphatase, activation of glucose-6-phosphoric dehydrogenase and inhibition of hexokinase. The changes were maximum one hour after the administration of the compound. The results show that a decrease of the intensity of glucose-6-phosphate formation and metabolism is one of the pathogenetic factors in the development of valekson-induced intoxication.
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PMID:[Activity of glucose-6-phosphate metabolism enzymes in the livers of rats with experimental valekson poisoning]. 20 53

The aim of the present work was to study by means of histochemical and chemical methods the 7-day course of changes in carbohydrate metabolism in the liver of male rats induced by a single dose of isoprenaline of 50 mg/kg administered subcutaneously. A statistically significant reduction was seen both in the level of free glycogen and lactate within 24 hours. The decrease of pyruvate level was not so marked. At the same time, there was increased, and within the hepatic lobules also extended activity of enzymes catalyzing glycogenolysis, i.e. alpha-glucan phosphorylase and particularly the branching Q-enzyme, glucose-6-phosphatase and LDH, whereas the level of malate and activity of SDH, which are constituents of the Krebs cycle, were found to be reduced. Cytochrome oxidase activity was changed after 24 hr compared to the controls. The obtained results indicate that an extensive glycogenolysis occurs in the liver of rats in the 24 hr following s.c. administration of isoprenaline, the major part of liver glycogen being degraded through glucose-6-phosphate to blood glucose and its metabolism via the Krebs cycle reduced. The observed metabolic changes are of reversible character and tend to normalize over the 2nd and 3rd day following isoprenaline administration.
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PMID:Study of histochemical and biochemical changes in the liver of rats induced by high doses of isoprenaline. 20 78


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