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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)

The experiment was carried out on rats, which were divided into three experimental and one control groups. The experimental animals were intraperitoneally injected with furfural in the dose of 58 mg/kg body weight for 30 days. In the liver samples obtained at autopsy, apart from routine staining with hematoxylin and eosin, estimation of the activity of the following enzymes was made: succinic dehydrogenase. NADH-tetrazol reductase, lactic dehydrogenase, glucose-6-phosphate, adenosine-triphosphatase, Ca-formol, glucose-6-phosphatase and acid phosphatase. Glycogen content was also evaluated. A temporary decrease in the activity of reactions for the enzymes of tissue respiration, an increase in the activity of glucose-6-phosphatase with a simultaneous decrease of glycogen content, activation of intracellular digestive processes, and inhibition of active transport through biological membranes were found in animals intoxicated with furfural.
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PMID:[Morphological and histochemical changes in the rat liver in chronic furfural poisoning]. 20 22

NADPH cytochrome c (cyt c) reductase and glucose-6-phosphatase, two enzymes thought to be restricted to the endoplasmic reticulum (ER) and widely used as ER markers, are present in isolated Golgi fractions assayed immediately after their isolation. Both enzymes are rapidly inactivated in fractions stored at 0 degrees C in 0.25 M sucrose, conditions which do not affect the activity of other enzymes in the same preparation. The inactivation process was shown to be dependent on time and protein concentration and could be prevented by EDTA and catalase. Morphological evidence shows that extensive membrane damage occurs parallel with the inactivation. Taken together with the immunological data in the companion paper, the findings indicate that the enzymes NADPH cyt c reductase and probably glucose-6-phosphate are indigenous components of Golgi membranes.
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PMID:Endoplasmic reticulum marker enzymes in Golgi fractions--what does this mean? 21 50

The enzyme histochemical characteristics of osteoclasts in imprints of the metaphyseal regions of femurs, from male kittens aged approximately 18 weeks, were investigated. A selected number of enzymes representative of a variety of metabolic pathways were studied. The enzyme profile, time for the first appearance of detectable reaction product, intensity of the reactions, and localization of the reaction products were noted. Osteoclasts are rich in enzymes, and metabolic pathways are well developed in respect of the utilization of the reduced coenzymes NADP and NADPH, succinic, malic, lactic, and isocitric acids, beta-hydroxybutyrate and glucose-6-phosphate, the reactions being mediated by the diaphorases and dehydrogenases. The activities of acid and neutral phosphatases, non-specific esterases, and leucine naphthylamidase were high in these cells. However, little or no activity was demonstrated in respect of glutamate and alpha-glycerophosphate dehydrogenases or of aryl sulphatase, glucose-6-phosphatase and alkaline phosphatase.
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PMID:Enzyme histochemical properties of kitten osteoclasts in bone imprint preparations. 21 79

The effects of added polyamines on carbamylphosphate (carbamyl-P):glucose phosphotransferase and glucose-6-phosphate (Glc-6-P) phosphohydrolase activities of rat hepatic D-Glc-6-P phosphohydrolase (EC 3.1.3.9) of intact and detergent-treated microsomes have been investigated. With the former preparation, in the presence of 1.4 mM phosphate substrate and 90 mM D-glucose (phosphotransferase), 1 mM spermine, spermidine, and putrescine activated Glc-6-P phosphohydrolase 67%, 57%, and 35%, respectively. Carbamyl-P:glucose phosphotransferase, under comparable conditions, was activated 57%, 34%, and 18%. NH+4 (0.25--5.0 mM) produced at best but a minor activation (0--14%), while poly(L-lysine) (Mr = 3400; degree of polymerization 16) equimolar relative to other polyamines with respect to ionized free amino groups activated the hydrolase 358% and the transferase 222%. Treatment of microsomes with the detergent deoxycholate reduced, but did not abolish, polyamine-induced activation. The stimulatory effects of polyamines persisted in the presence of excess catalase, indicating their independence from H2O2 formation; and were eliminated in the presence of Ca2+. Kinetic analysis revealed that all tested polyamines decreased the apparent Michaelis constant values for carbamyl-P and Glc-6-P, but had no effect on the Km for glucose. Poly(L-lysine) increased the V value for both Glc-6-P phosphohydrolase and apparent V values for phosphotransferase extrapolated to infinite concentrations of either carbamyl-P or glucose. The other tested polyamines elevated only this last velocity parameter. It is proposed that a major mechanism by which polyamines activate glucose-6-phosphatase-phosphotransferase is through their electrostatic interactions with phospholipids of the membrane of the endoplasmic reticulum of which this enzyme is a part. Conformational alterations thus induced may in turn affect catalytic behavior. It is suggested that polyamines, or similar positively charged peptides, might participate in the cellular regulation of synthetic and hydrolytic activities of glucose-6-phosphatase.
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PMID:Stimulation by polyamines of carbamylphosphate:glucose phosphotransferase and glucose-6-phosphate phosphohydrolase activities of multifunctional glucose-6-phosphatase. 22 Oct 50

Modification of microsomal membranes in vivo and in vitro results in changes of the glucose-6-phosphate and inorganic pyrophosphate phosphohydrolase activities of liver microsomal glucose-6-phosphate phosphohydrolase (EC 3.1.3.9). It was demonstrated that the glucose-6-phosphate phosphohydrolase activity of glucose-6-phosphatase depends on the content of phosphatidylethanolamine in the microsomal membranes, whereas the inorganic pyrophosphate phosphohydrolase activity seems to be dependent on the phosphatidylserine content. It is assumed that the regulation of the corresponding enzyme activities by these phospholipids is performed by the same allosteric mechanism in vitro and in vivo.
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PMID:[Role of lipids in regulation of microsomal glucose-6-phosphatase activity after modification of mcirosomes in vivo and in vitro. Effect of phospholipid effectors on the activity of glucose-6-phosphatase]. 22 75

Kinetic studies indicate that glucose-6-phosphatase is a multifunctional enzyme. a) Phosphohydrolase activities. The mannose-6-phosphatase activity is low (Km = 8 mM, VM = 90 nmoles. min-1mg-1). The enzyme shows a strong affinity for glucose-6-phosphate (Km = 2.5 mM, VM = 220 nmoles.min-1mg-1). beta-glycerophosphate (K1 = 30 mM), D-glucose (Ki = 120 mM) are mixed type inhibitors; pyrophosphate (Ki = 2 mM) is a non competitive one. b) Phosphotransferase activities. Di and triphosphate adenylic nucleosides or phosphoenol pyruvate are not substrates. Carbamylphosphate serves as a phosphoryl donor with D-glucose as acceptor. The phosphate transfer is consisstent with a random mechanism in which the binding of one substrate increases the enzymes affinity for the second substrate. Apparent Km values for carbamyl-phosphate range from 5.2 mM (D-glucose concentration leads to infinity) to 8 mM (D-glucose concentration leads to 0). The corresponding apparent Km values for D-glucose are 59 mM (carbamyl-phosphate concentration leads to infinity) to 119 mM (carbamyl-phosphate concentration leads to 0). Maximal reaction velocity with infinite levels of both substrates is 270 nmoles.min-1.mg-1. Pyrophosphate is a poor phosphoryl donnor (Km = 55 mM with D-glucose concentration 250 mM). In addition we do not find any latency; detergents, namely sodium deoxycholate, Triton X 100 do not affect or inhibit glucose-6-phosphatase activity.
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PMID:[Monkey liver microsomal glucose-6-phosphatase]. 23 60

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

An attempt has been made to show that the increase in enzyme activities in sera of pregnant women found with glucose-6-phosphate and adenosine 5'-monophosphate as substrates (described as glucose-6-phosphatase and 5'-nucleotidase) was due to the increase in alkaline phosphatase. The three enzyme activities has pH optima and heat stability characteristics of alkaline phosphatase. The response to the action of inhibitors and activators was typical for alkaline phosphatase. There was an identical increase in all three enzyme activities during pregnancy. As a control similar investigations were made with liver and placental tissue extracts.
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PMID:The serum activity of glucose-6phosphatase and 5'-nucleotidase during human pregnancy. 23 76

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

More than ten patients with glycogen-storage disease, which were classified as patients with glycogenosis of the I type--deficiency in glucose-6-phosphatase) on the basis of clinical data and biochemical analyses in vivo, were detected within the last few years. But activity of glucose-6-phosphatase was found to be normal in biopsy of samples of the liver tissue obtained from these patients. This disease was termed as glycogenosis of the Ib type. A hypothesis is advanced, according to which the discrepancy in data on biochemical study of the patients in vivo and in vitro is due to absence of a specific permease in liver tissue, which transfers glucose-6-phosphate from cytosol onto the innesurface of membranes of cytoplasmic network, where glucose-6-phosphatase is located.
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PMID:[Disordered glucose-6-phosphate transport as a possible cause of glycogenosis type Ib]. 38 25


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