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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)

Arion et al; (Arion, W. J., Wallin, B. K., Lange A. J., and Ballas, L. M. (1975) Mol. Cell. Biochem. 6, 75-83) propsed a model for glucose-6-phosphatase in which the substrate was transported across the microsomal membrane by a carrier before hydrolysis on the cisternal side. Evidence to support this model has been obtained by studying the inhibition of the enzyme by pyridoxal-P. Pyridoxal-P was a linear noncompetitive inhibitor of glucose-6-phosphatase (EC 3.1.3.9) in freshly isolated ("intact") microsomes from rat liver. Pyridoxol-P was a much less effective inhibitor and no inhibition was observed with pyridoxamine-P. When microsomes were subjected to nitrogen cavitation, treatment with solium deoxycholate, or glutaraldehyde fixation, the Km of glucose-6-phosphatase for glucose-6 P decreased from approximately 6 mM to approximately 2.5 mM; the corresponding change in the Vmax ranged from-10% to +40%. The same procedures decreased the inhibition of glucose-6-phosphatase by pyridoxal-P several-fold. No inhibition by pyridoxal-P was observed in a preparation of glucose-6-phosphatase purified approximately 20 fold (on the basis of Vmax) from micoromes. A nondialyzable inhibitor was apparently formed when intact microsomes were reacted with pyridoxal-P and NaBH4; this inhibition was also reversed by procedures which changed the kinetic properties of glucose-6-phosphatase.
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PMID:Relationship between microsomal membrane permeability and the inhibition of hepatic glucose-6-phosphatase by pyridoxal phosphate. 17 64

In this first paper of a series comparing the membranes of normal lymphocyte populations from male outbred Syrian hamsters with those of neoplastic transformants (GD 248) induced by simian virus 40, a method is described for the isolation of representative plasma membrane (PM) fragments from both cell types. Multiple criteria were used to monitor the purity and yield of PM material after cell disruption by nitrogen cavitation and after membrane fractionation by a combination of differential centrifugation and isopyknic ultracentrifugation in dextran density gradients. Lactoperoxidase-catalyzed radioiodination before cell disruption was used as an extrinsic surface marker; Na+,K+-activated ATPase, as well as alkaline phosphatase, was used as intrinsic functional PM markers. The distribution of nuclei, mitochondria, lysosomes, and endoplasmic reticulum (ER) during fractionation was monitored by the measurement of DNA, succinate dehydrogenase and monoamine oxidase, beta-glucuronidase and glucose-6-phosphatase, and NADH:lipoamide oxidoreductase, respectively. According to the three PM markers employed, a 15- to 20-fold purification (over homogenate) and a PM yield of about 65% were obtained for both cell categories, with negligible contamination by DNA, mitochondria, lysosomes, and er. The procedure also allowed recovery of 60% of the mitochondria free of other cell elements.
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PMID:Membranes of normal hamster lymphocytes and lymphoid cells neoplastically transformed by simian virus 40. I. High-yield purification of plasma membrane fragments. 18 92

Plasma membranes, microsomes, and mitochondria were isolated from mouse fibroblast (LM) suspension cells by modification of several established procedures. Choline analogues such as N,N'-dimethylethanolamine, N-monomethylethanolamine, or ethanolamine were incorporated in vivo into phospholipids of all three cell fractions studied, but to varying degrees depending on the type of analogue used. The in vivo incorporation of these bases into membrane phospholipids produced no significant effect on the activities of seven membrane-bound enzymes: (Na+, K+)-ATPase, 5'-nucleotidase (plasma membranes); TPNH-cytochrome c reductase, glucose-6-phosphatase, inosine diphosphatase (microsomes); and succinate cytochrome c reductase (mitochondria). The incorporation of base analogues into phospholipids was accompanied by several compensatory mechanisms. (a) The quantity of both phosphatidylcholine and phosphatidylethanolamine decreased up to 75% and 50% respectively in 3 days. (b) The molar ratio of desmosterol/phospholipid in the plasma membranes of LM cells grown in suspension culture in the presence of choline analogues decreased from 0.65 to 0.45. (c) The percentage of lysophosphatidylcholine increased over 2-fold in the phospholipid of all subcellular fractions studied. The quantity of lysophosphatidylcholine was directly proportional to the number of methyl groups on the nitrogen atom of the base analogue supplemented to the cells. This was a specific effect since the quantity of lysophosphatidylethanolamine, the other major lysophospholipid, remained unchanged. (d) The ratio of zwitterionic phospholipids to acidic phospholipids remained relatively constant in all isolated membrane fractions regardless of analogue supplementation. Neither increase in the degree of unsaturation nor shortening of fatty acid chain length was noted in response to analogue supplementation.
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PMID:Isolation and characterization of subcellular membranes with altered phospholipid composition from cultured fibroblasts. 95 75

Renal microsomes isolated on day 3 from cisplatin (CDDP, single i.p. injection, 4 or 6 mg/kg)-treated rats were monitored for their susceptibility to lipid peroxidation as compared with microsomes from rats treated with carboplatin (CBDCA, 30 mg/kg), transplatin (TDDP, 6 mg/kg) or CDDP hydrolysis products (4 or 6 mg/kg) or from control animals. Cephaloridine (1 g/kg daily for 4 days, i.p. injection) was used as a positive control. The effect of CDDP on renal microsomal glucose-6-phosphatase activity was investigated in vivo and in vitro. Following treatment with CDDP and CDDP hydrolysis products vs CBDCA and TDDP treatment, microsomes revealed an enhanced susceptibility to lipid peroxidation in a Fe2+ and/or ascorbic acid stimulation system. Increased lipid peroxidation, expressed as an increase in malondialdehyde (MDA) generation, paralleled the alterations in body and kidney weight and the elevations of plasma creatinine and blood urea nitrogen concentrations. Injection of the antioxidant N,N'-diphenyl-p-phenylenediamine (DPPD, 0.5 g/kg, i.p.) at 24 h prior to CDDP treatment abolished the increased vulnerability of renal microsomes to lipid peroxidation. In vivo, only CDDP hydrolysis products exhibited a significant inhibitory effect on renal glucose-6-phosphatase activity. In vitro, rat renal and hepatic microsomal glucose-6-phosphatase activity was decreased by CDDP both time- and concentration-dependently. Nephrotoxicity induced by CDDP and CDDP hydrolysis products might be attributable to iron-dependent lipid peroxidation and microsomes might represent target organelles on a subcellular level.
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PMID:Iron- and ascorbic acid-induced lipid peroxidation in renal microsomes isolated from rats treated with platinum compounds. 193 47

Growth of cells of the potentially zoopathogenic fungus Basidiobolus haptosporus on a nutritionally defined medium with xanthine or urate as the nitrogen source results in greatly increased populations of microbodies. Modified Gomori procedures at the electron microscopic level suggested the single limiting membrane (and in some cases the granular matrix) of immature microbodies to be the exclusive subcellular locale(s) of alkaline phosphatase, 5'-nucleotidase and nucleoside diphosphatase activities. When grown in the presence of low inorganic phosphate, additional alkaline phosphatase activity was further identified cytochemically at and along profiles of endoplasmic reticulum and on inclusions previously described as "double-membraned vesicles". Cytochemical localization of acid phosphatase at microbody membranes was minimal if not ambiguous; Mg++-dependent adenosine triphosphatase and glucose-6-phosphatase were not identified at these locales. Quantitative biochemical estimates of alkaline phosphatase activity levels in particulate fractions initially increased with age of cells, perhaps as a function of the cultural induction and marked increase in immature microbody populations. We suggest that this enzyme may participate in some manner with protein translocation mechanisms associated with microbody biogenesis, ontogeny, and/or physiological function.
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PMID:Electron cytochemical demonstration of phosphatase activity with microbody membranes of Basidiobolus haptosporus. 282 62

Oxidation of diethyldithiocarbamate (DTC) to disulfiram (DS) by liver microsomes was tested in vitro by using a copper-DTC chelate formation reaction after the conversion of DS to DTC by glutathione (GSH). In the presence of NADPH, microsomes produced DS from DTC in both the free and microsome-bound forms, the former being greater than the latter. DS production was dependent on NADPH and DTC concentrations, and incubation time. Increases in microsomal concentrations, up to a certain level, also increased the free and total DS production. NADH was only somewhat effective, both the exposure to a nitrogen atmosphere and heat-denaturation of the microsomes suppressed the reaction. Preincubation of microsomes with both DTC and NADPH markedly decreased aniline hydroxylase, p-nitroanisole O-demethylase and glucose-6-phosphatase activities, and moderately decreased NADH-ferricyanide and NADH-cytochrome c reductase, but NADPH-cytochrome c reductase was minimally affected. DTC alone had only slight effects on the activities. DS also decreased these enzyme activities, particularly glucose-6-phosphatase; the loss of NADPH-cytochrome c reductase activity being protected in the presence of NADPH. GSH almost completely prevented the loss of microsomal enzyme activities induced by DTC and NADPH except for the drug metabolizing activities, in which protection was incomplete. The microsomal oxidation of DTC to DS could play a role in the action of DS in the liver, since DS is rapidly degradated to DTC in vivo.
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PMID:Oxidation of diethyldithiocarbamate to disulfiram by liver microsomes in the presence of NADPH and subsequent loss of microsomal enzyme activity in vitro. 285 81

The demonstration of the ultrastructural localization of glucose-6-phosphatase in rat liver is hampered by penetration problems of the medium as appears from ultrathin cross-sections of vibratome sections. Besides the plasma membrane, also the cytoplasm forms a serious barrier for the penetration of the medium constituents. Prolonged preincubation for as long as 48 h at 4 degrees C in the complete incubation medium could not prevent the penetration hindrance. However, when employing 30 micron vibratome sections from tissue blocks that were frozen in melting nitrogen, the penetration hindrance was prevented.
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PMID:Prevention of penetration hindrance in cerium-based glucose-6-phosphatase cytochemistry by freezing tissue in melting nitrogen. 298 63

Hematological, biochemical, histoenzymological, and histopathological changes in serum and tissues were studied in chickens during outbreaks of nephritis. Hematological studies revealed normocytic-normochromic anemia characterized by increased total erythrocyte counts, hemoglobin, packed cell volume, and erythrocyte sedimentation rate. Albumin-to-globulin ratio and sodium levels in serum, glucose in blood, and alkaline phosphatase and glucose-6-phosphatase in liver and kidneys were decreased. Glutamate pyruvate transaminase, uric acid, non-protein-nitrogen, and potassium levels in serum were increased. No significant change in the calcium, phosphorus, and total protein levels in serum was observed. These changes were directly related to the severity of the nephritis.
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PMID:Clinicopathological, hematological, and biochemical studies in some outbreaks of nephritis in poultry. 407 33

The metabolic response to the first fast experienced by all mammals has been studied in the newborn rat. Levels of fuels and hormones have been compared in the fetal and maternal circulations at term. Then, after cesarean section just before the normal time of birth, sequential changes in the same parameters were quantified during the first 16 h of the neonatal period. No caloric intake was permitted, and the newborns were maintained at 37 degrees C. Activities of three key hepatic enzymes involved in glucose production were estimated. Marked differences in maternal and fetal hormones and fuels were observed. Lower levels of glucose, free fatty acids, and glycerol but higher levels of lactate, alpha-amino nitrogen, alanine, and glutamine were present in the fetus. Pyruvate, glutamate, and ketone bodies were not significantly different. The combination of a strikingly higher fetal immunoreactive insulin and a slightly lower immunoreactive glucagon (pancreatic) resulted in a profound elevation in the insulin-to-glucagon ratio, a finding consistent with an organism in an anabolic state. The rat at birth presents a body composition with respect to fuels available for mobilization and conversion which is dominated by carbohydrate and protein, since little fat is present. However, at birth a transient period of hypoglycemia occurred, associated with a rapid fall in insulin and rise in glucagon, causing reversal of the insulin-to-glucagon relationship toward ratios such as were observed in the mother. After a lag period, hepatic activities of phosphorylase, glucose-6-phosphatase, and phosphoenolpyruvate carboxykinase increased. Concurrent with these enzyme changes, the blood glucose returned to levels at or above those of the fetus. Interestingly, the fall observed in levels of the gluconeogenic precursors, lactate and amino acids, preceded the rise in enzyme activities and restoration of blood glucose. After 4 h, however, hypoglycemia recurred, during a period of decreasing hepatic glycogen content and blood lactate, pyruvate, and glycerol levels but of stable or increasing amino acid concentrations. Hepatic gluconeogenesis in this phase of depleted glycogen stores was insufficient to maintain euglycemia. Substrates derived from fat showed early changes of smaller magnitude. The rise in free fatty acids which occurred was less than twofold the value at birth, though this rise persisted up to 6 h. Whereas glycerol rose transiently, acetoacetate did not change and beta-hydroxybutyrate concentration fell. Both ketone bodies showed a marked rise at 16 h. at a time of diminished free fatty acid levels. Plasma growth hormone, though higher in the fetal than the maternal circulation, showed no consistent change during the period of observation. The changes in levels of the endocrine pancreatic hormones at birth were appropriate in time, magnitude, and direction to be implicated as prime regulators of the metabolic response during the neonatal period in the rat.
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PMID:Fuels, hormones, and liver metabolism at term and during the early postnatal period in the rat. 475 Apr 49

The cytochemical localization of glucose-6-phosphatase (G6Pase) and its biochemical quantification were studied in isolated and cultured adult rat parenchymal cells. Appropriate technical conditions were chosen to assume adequate ultrastructural preservation and retention of enzyme activity. Isolated hepatocytes separated by collagenase perfusion were shortly fixed in glutaraldehyde and entrapped in a pellet of fibrin. Frozen sections, 50 microns in thickness were incubated for cytochemical demonstration of G6Pase, in a slightly modified Wachstein-Meisel medium. Hepatocytes in culture, fixed for 1 min in glutaraldehyde, were impregnated in a 10% cryoprotective glycerol solution and quickly frozen in liquid nitrogen at -170 degrees C in order to induce penetration of the substrate. In these conditions, a homogeneous distribution of the enzyme was observed in both isolated and cultured cells. The cytochemical reaction appears continuous in the smooth and rough endoplasmic cisternae and in the nuclear envelope. Lead phosphate deposits, although evenly distributed, are reduced in intensity after 48 h culture. Biochemical determinations reveal the presence of a high specific enzymatic activity in isolated cells (108 nmolP/min/mg proteins), which decreases in culture, respectively to 70 and 50% of the original value, after 24 and 48 h culture. G6Pase induction by glucagon was obtained after 48 and 72 h in culture.
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PMID:Glucose-6-phosphatase distribution in isolated and cultured adult rat hepatocytes. 626 35


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