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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)

Hyperinsulinemia was produced in fetal rhesus monkeys for 21 days in the last third of gestation by subcutaneous pork insulin injected at 19 U a day. Plasma insulin concentrations in treated fetuses (N = 4) were 3525 microU/ml. There was no difference in paired pre- and post-treatment fetal plasma glucose concentration. Activity of the hepatic enzymes that promote glucose utilization (glucokinase and hexokinase) and glycolysis (phosphofructokinase, pyruvate kinase, and pyruvate dehydrogenase) was unaffected. Similarly, glycogen metabolism enzymes (active and inactive synthase and phosphorylase) were unaltered. Two gluconeogenic enzymes (PEPCK and glucose-6-phosphatase) were diminished in the treated group compared with controls. Fetal hyperinsulinemia enhanced lipogenic and NADPH-producing enzyme activities, as evidenced by a twofold increase in fatty acid synthase and in citrate cleavage enzyme activity. Malic enzyme was absent. Hyperinsulinemia with euglycemia (1) increases the activity of enzymes that participate in lipogenesis, (2) decreases some of those controlling gluconeogenesis, and (3) has no effect on the enzymes of glycolysis.
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PMID:Chronic hyperinsulinemia in the fetal rhesus monkey: effects on hepatic enzymes active in lipogenesis and carbohydrate metabolism. 22 50

The activities of two gluconeogenic enzymes, glucose-6-phosphatase and fructose-1,6-diphosphatase were examined in the normal and intrauterine growth retarded (IUGR) rat during the first 5 days of life. The fructose-1,6-diphosphatase activity, 1.54 +/- 0.10 mumol/min/g liver (means +/- SEM) in control and 1.47 +/- 0.20 in the IUGR rats, increased in both groups on days 2--4 but remained significantly lower in the IUGR rats through day 4 (4.53 +/- 0.6 mumol/min/g liver in control and 3.09 +/- 0.22 mumul/min/g liver in the IUGR rats, P less than 0.01). The glucose-6-phosphatase activity increased similarly in both groups. The weight of the IUGR rats remained lower through the third postnatal day (6.47 +/- 0.42 compared to 8.64 +/- 0.27 g in control rats). Blood glucose concentrations at birth were 117 +/- 11 mg/dl in control rats and 73 +/- 11 mg/dl in the IUGR rats (P less than 0.01). Although the glucose concentrations increased in both groups on days 2--4, the IUGR rats maintained relatively lower levels (P less than 0.01). The results indicate that IUGR fetal rats do not have augmented gluconeogenesis in spite of hypoglycemia. In addition, effective gluconeogenesis in the neonatal period appears to be delayed.
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PMID:Fructose-1,6-diphosphatase and glucose-6-phosphatase in newborn rats with intrauterine growth retardation. 23 Sep 54

During hepatic regeneration a drop in the liver glycogen content along with a lower blood glucose level have been observed. These data are difficult to correlate with the rise of blood glucagon and the drop of insulin shown at the same times after partial hepatectomy. Therefore, liver glucose-6-phosphatase activity has been studied at 1.5, 4, 15 and 24 h, since that enzyme is involved in the release of glucose from the cell. 4 and 15 h after partial hepatectomy a remarkable decrease in glucose-6-phosphatase activity is observed. These results are discussed in view of the higher metabolic demand of regenerating liver.
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PMID:[Activity of glucose-6-phosphatase during liver regeneration]. 23 47

1. Glucokinase was absent from chicken liver and only the low Km hexokinases, inhibited by AMP, ADP but not ATP, were present. 2. The Km of chicken liver glucose-6-phosphatase for glucose-6-phosphate was reduced from 5.65 to 3.75 mM following starvation, and the enzyme was inhibited by glucose. 3. Starvation of chickens for 24 hr slightly lowered the hexokinase activity and doubled glucose-6-phosphatase activity; it did not change subcellular distribution of the enzymes. Oral glucose rapidly restored the activities to fed values. 4. It was concluded that glucose uptake into, and efflux from, chicken hepatocytes, was regulated by the activity and kinetic characteristics of glucose-6-phosphatase and by the glucose-6-phosphate concentration, and that the hexokinases had little regulatory function.
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PMID:Glucose phosphorylation and dephosphorylation in chicken liver. 23 87

The presence of carbamyl-phosphate:glucose phosphotransferase in liver nuclei of five species of mammals and birds is demonstrated. The activity is confined to nuclear membranes and is due exclusively to multifunctional glucose-6-phosphatase-phosphotransferase (D-glucose-6-phosphate phosphohydrolase; EC 3.1.3.9). The nuclear enzyme constitutes approximately 16 to 19 percent of total hepatic glucose-6-phosphatase-phosphotransferase. Carbamyl-phosphate:glucose phosphotransferase and glucose-6-P phosphohydrolase activities of membrane of chicken liver nuclei are shown to be catalytically identical with the maximally activated microsomal enzyme. A correspondence is seen in two-substrate kinetic double reciprocal plots, K-m or apparent K-m values for the various substrates, K-i values for the competitive inhibitors P-i and ATP, and pH-activity profiles. Comparative studies were carried out with various intact, disrupted, and detergent-dispersed membranous preparations by a combination of enzyme kinetic and electron microscopic techniques. It is concluded that (a) intimate interrelationships exists between catalytic behavior of this enzyme and morphological integrity of membranes of which the enzyme is a part; (b) activities of the enzyme of nuclear membrane appear quite available for physiological phosphorylative functions; and (c) interrelationships between membrane morphology and catalytic behavior of this membrane-bound enzyme may well be involved in the bioregulation of this complex, multifunctional enzyme system.
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PMID:Carbamyl phosphate: glucose phosphotransferase and glucose-6-phosphate phosphohydrolase of nuclear membrane. Interrelationships between membrane integrity, enzymic latency, and catalytic behavior. 23 53

A model for microsomal glucose 6-phosphatase (EC 3.1.3.9) is presented. Glucose 6-phosphatase is postulated to be resultant of the coupling of two components of the microsomal membrane: 1) a glucose 6-phosphate - specific transport system which functions to shuttle the sugar phosphate from the cytoplasm to the lumen of the endoplasmic reticulum; and 2) a catalytic component, glucose-6-P phosphohydrolase, bound to the luminal surface of the membrane. A large body of existing data was shown to be consistent with this hypothesis. In particular, the model reconciles well-documented differences in the kinetic properties of the enzyme of untreated and modified microsomal preparations. Characteristic responses of the enzyme to changes in nutritional and hormonal states may be attributed to adaptations which alter the relative capacities of the transport and catalytic components.
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PMID:On the involvement of a glucose 6-phosphate transport system in the function of microsomal glucose 6-phosphatase. 23 36

1) Rat liver microsomes exhibit only a weak hydrolyzing activity towards galactose 6-phosphate. Disruption of the microsomal vesicles does not change the apparent Michaelis constant for this substrate but enhances the apparent maximum velocity. 2) The inhibition of microsomal glucose-6-phosphatase (EC 3.1.3.9) by galactose 6-phosphate is of the competitive type in intact and disrupted microsomal vesicles, suggesting that both substrates are hydrolyzed by the same enzyme. 3) The high degree of latency found for the hydrolysis of galactose 6-phosphate compared to glucose 6-phosphate indicates the presence of a carrier for glucose 6-phosphate in the microsomal membrane. 4) Since glucose as a product is not trapped inside the microsomal vesicles, this sugar probably is able to penetrate the microsomal membrane.
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PMID:Membrane effects on hepatic microsomal glucose-6-phosphatase. 24 94

Two patients with apparent clinical manifestations of glycogen storage disease were described. The curves obtained upon glucose and adrenalin tolerance tests were indicative of glycogen storage disease Type I. Liver biopsies showed the increased glycogen concentration; however, the activities of the enzymes involved in glycogen metabolism, including glucose-6-phosphatase activity, were within normal limits or even slightly enhanced. On the basis of the biochemical data, Type Ib glycogenosis was diagnosed. The analytical ultracentrifugation studies of serum lipoproteins of those patients showed that concentration of very low density lipoproteins was considerably increased.
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PMID:Two cases of unusual Type I glycogenosis. 27 30

Other investigators have shown that fructose infusion in normal man and rats acutely depletes hepatic ATP and P(i) and increases the rate of uric acid formation by the degradation of preformed nucleotides. We postulated that a similar mechanism of ATP depletion might be present in patients with glucose-6-phosphatase deficiency (GSD-I) as a result of ATP consumption during glycogenolysis and resulting excess glycolysis. The postulate was tested by measurement of: (a) hepatic content of ATP, glycogen, phosphorylated sugars, and phosphorylase activities before and after increasing glycolysis by glucagon infusion and (b) plasma urate levels and urate excretion before and after therapy designed to maintain blood glucose levels above 70 mg/dl and thus prevent excess glycogenolysis and glycolysis. Glucagon infusion in seven patients with GSD-I caused a decrease in hepatic ATP from 2.25 +/- 0.09 to 0.73 +/- 0.06 mumol/g liver (P <0.01), within 5 min, persisting in one patient to 20 min (1.3 mumol/g). Three patients with GSD other than GSD-I (controls), and 10 normal rats, showed no change in ATP levels after glucagon infusion. Glucagon caused an increase in hepatic phosphorylase activity from 163 +/- 21 to 311 +/- 17 mumol/min per g protein (P <0.01), and a decrease in glycogen content from 8.96 +/- 0.51 to 6.68 +/- 0.38% weight (P <0.01). Hepatic content of phosphorylated hexoses measured in two patients, showed the following mean increases in response to glucagon; glucose-6-phosphate (from 0.25 to 0.98 mumol/g liver), fructose-6-phosphate (from 0.17 to 0.45 mumol/g liver), and fructose-1,6-diphosphate (from 0.09 to 1.28 mumol/g) within 5 min. These changes, except for glucose-6-phosphate, returned toward preinfusion levels within 20 min. Treatment consisted of continuous intragastric feedings of a high glucose dietary mixture. Such treatment increased blood glucose from a mean level of 62 (range 28-96) to 86 (range 71-143) mg/dl (P <0.02), decreased plasma glucagon from a mean of 190 (range 171-208) to 56 (range 30-70) pg/ml (P <0.01), but caused no significant change in insulin levels. Urate output measured in three patients showed an initial increase, coinciding with a decrease in plasma lactate and triglyceride levels, then decreased to normal within 3 days after treatment. Normalization of urate excretion was associated with normalization of serum uric acid. We suggest that the maintenance of blood glucose levels above 70 mg/dl is effective in reducing serum urate levels and that transient and recurrent depletion of hepatic ATP due to glycogenolysis is contributory in the genesis of hyperuricemia in untreated patients with GSD-I.
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PMID:ATP depletion, a possible role in the pathogenesis of hyperuricemia in glycogen storage disease type I. 27 29

I. In three separate experiments, four groups of five to eight young male rats were fed either (i) a high-protein diet, for which the net dietary protein:total metabolizable energy ratio (NDp:E) was 0-1 (HP diet); or (ii) a low-protein diet, for which NDp:E was 0-04 (LP diet). In both these groups, food intake was ad lib. In group (iii) the HP diet was given in an amount approximately equal to that taken by the LP group fed ad lib. (HP-restricted). In group (iv) rats were fasted for 48 h after receiving the HP diet (HP-fasted). Each experiment lasted 4 weeks. 2. In the LP and HP-restricted groups, food intake was about 50% of that of the HP rats, while body-weight, after 4 weeks on diet was about 35% and 55% of that of HP rats, for LP and HP-restricted respectively. Both groups of malnourished rats gained some weight during the experiment. 3. Measurements of oral glucose tolerance and plasma insulin levels were made in the fourth week. LP and HP-restricted rats both showed low fasting insulin levels and low insulin to glucose ratios during the glucose tolerance tests; the LP rats were more seriously affected. 4. At the end of the fourth week the rats were killed and blood, liver and gastrocnemius muscle were analysed. LP rats showed specifically and consistently low values for haemoglobin and plasma protein concentration, and low activities of hepatic glucose-6-phosphatase (EC 3-1-3-9) and of alanine aminotransferase (EC 2.6.1.2) in liver and muscle. The activity of hepatic aspartate aminotransferase (EC 2.6.1.1) was, if anything, increased. The plasma amino acid concentrations and ratios showed a specific fall in branched-chain amino acids. Liver fat concentration was consistently elevated. The HP-restricted rats had normal values for haemoglobin, plasma protein andliver fat, and near-normal values for plasma amino acids. Hepatic alanine aminotransferase showed increased activity compared with HP rats, but muscle alanine aminotransferase showed reduced activity. The HP-fasted rats had increased haemoglobin, plasma protein and liver fat concentration, and very low liver glycogen concentrations. Hepatic alanine aminotransferase activity was elevated. Plasma alanine concentration was specifically reduced. 5. The results are consistent with suppression of gluconeogenesis, liver dysfunction and essential amino acid deprivation in LP rats. These biochemical changes found in rats on a low intake of a diet of low protein and high carbohydrate value are similar to those found in kwashiorkor. An equally low intake of a diet of good protein value (HP-restricted) led to marginally better growth, accompanied by biochemical signs of increased gluconeogenesis, analogous to those reported for nutritional marasmus. This nutritional state was not biochemically identical with that of acute fasting. 6. The results are discussed in terms of the consistency of the rat model, and its contribution to understanding biochemical changes found in infant malnutrition.
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PMID:Biochemical characteristics of different forms of protein-energy malnutrition: an experimental model using young rats. 40 28


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