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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)

Glucose-6-phosphatase (glucose-6-phosphohydrolase and its associated phosphotransferase activities) was determined in brain tissue and in several preparations derived from brain tissue. These included purified capillaries and established cell lines of neuronal or glial origin. Since it has been suggested that glucose-6-phosphatase may be involved in sugar transport, the characteristics of that process were examined in these preparations. The pattern of uptake of 2-deoxy-D-glucose in four cell lines was shown to involve transport of the analog across the cell membrane that was more rapid than the subsequent phosphorylation of the sugar in the intracellular compartment. In the remaining cell lines and in purified capillaries, phosphorylation of 2-deoxy-D-glucose was at least as rapid as uptake. No differences could be found between the cells in these two categories with respect to amount or localization of glucose-6-phosphatase, ability to phosphorylate 3-O-methyl-D-glucose, or ability to phosphorylate extracellular and intracellular 2-deoxy-D-glucose. In the course of these experiments, it was found that there was a rapid efflux of 2-deoxy-D-glucose from cells that had taken up this sugar. The efflux involves a dephosphorylation step catalyzed by intracellular phosphatase that releases free sugar in the cytoplasm. Glucose-6-phosphatase thus probably has no major role in the phosphorylation of glucose in brain cells, but acts in the more conventional sense, i.e. as a phosphohydrolase.
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PMID:Cerebral glucose-6-phosphatase and the movement of 2-deoxy-D-glucose across cell membranes. 2 Apr 41

An insoluble phosphoprotein of rat brain acquires radioactivity from inorganic phosphate more rapidly during sleep than during wakefulness. It was purified in two ways. The first was solvent delipidation of brain tissue followed by preparative sodium dodecyl sulfate polyacrylamide gel electrophoresis. The second was sucrose gradient centrifugation of a brain homogenate to remove myelin, and gel filtration on Sephadex G-100 and adsorption chromatography on DEAE-Sephadex in the presence of sodium deoxycholate. The products were homogeneous within the limits of the analytical methods used. The apparent molecular weight of the phosphoprotein was 28,000 on sodium dodecyl sulfate polyacrylamide gels, but was much higher in the presence of sodium deoxycholate. The protein had a high content of aspartic and glutamic acids compared to basic amino acids. Analysis of a base hydrolysate, as well as studies of the kinetics of hydrolysis, showed that the radioactive phosphorus was attached to histidine. The NH2-terminal residue was identified as isoleucine. The phosphoprotein purified by the second method was enzymatically active. When it was incubated in vitro with a 32P-labeled supernatant fraction from rat brain (and later with glucose [6-32P]phosphate), a radioactive phosphorylated protein intermediate was formed. Exploration of the several enzymatic activities of the preparation indicated close correspondence to those reported for the glucose-6-phosphatases of liver and kidney. Glucose-6-phosphatase activity was found in all parts of the brain in the membranous subcellular fractions of neurons. It was shown to be co-purified with the sleep-related phosphoprotein. This report constitutes, we believe, the first complete purification of glucose-6-phosphatase from any tissue and an instance in which a change in the state of a cerebral enzyme has been linked to a normal change in the physiological state of the brain.
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PMID:Purification of cerebral glucose-6-phosphatase. An enzyme involved in sleep. 16 41

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

Electron microscopic cytochemistry was used to determine the localization of five phosphatase enzymes-glucose-6-phosphatase, inosine diphosphatase, thiamine pyrophosphatase, acid phosphatase, and adenosine triphosphatase-in control human testes. Glucose-6-phosphatase occurred in the endoplasmic reticulum and nuclear envelope of Sertoli cells, Leydig cells and primitive spermatogonia, but was not observed in more advanced spermatogenic cells. The presence of glucose-6-phosphatase activity paralleled the presence of glycogen in spermatogenic cells, i.e., both occurred in type AL and AD spermatogonia but not in type AP or B spermatogonia or in more advanced spermatogenic cells. Inosine diphosphatase activity was found in the endoplasmic reticulum, nuclear envelope, and Golgi complex of Sertoli cells and all spermatogenic cells except late spermatids. Additionally, inosine diphosphatase activity was localized at the junctions between Sertoli cells and late spermatids, but was not associated with any other plasma membrane. Thiamine pyrophosphatase reaction product was found in the Golgi bodies of Sertoli cells and in spermatogenic cells through immature spermatids. Neither inosine diphosphatase nor thiamine pyrophosphatase was observed in the Golgi bodies of spermatids during acrosomal formation. Acid phosphatase activity was found in lysosomes of spermatogonia, spermatocytes, and spermatids, in lysosomes of Leydig cells, and in lysosomes, lipofuscin bodies, and Golgi cisternae of Sertoli cells. It is thought that Sertoli lysosomes play a role in the phagocytosis of degenerating germ cells; however, the role of spermatogenic or Leydig lysosomes is unknown. Adenosine triphosphatase activity occurred at the interfaces between two spermatogonia, and between Sertoli cells and spermatogonia, but was not observed in the spaces between two Sertoli cells, two spermatocytes, two spermatids, or between Sertoli cells and spermatocytes, or between Sertoli cells and spermatids.
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PMID:The fine structural localization of testicular phosphatases in man: the control testis. 17 58

For the biochemical characterization of a new transplantable hepatoma derived from the MC-29 virus-induced liver tumor, the macromolecular content and the inducibility of glucose-6-phosphatase, glucose-6-phosphate dehydrogenase, and aryl hydrocarbon hydroxylase were compared in chicken liver and in this hepatoma. The alteration of the nucleocytoplasmic ratio was deduced from measurements of DNA, RNA, protein, and phospholipid contents of the whole cell homogenate and cell fractions. The increased nuclear and decreased cytoplasmic content of macromolecules suggests a dominancy of the nuclei in the tumor cells. Glucose-6-phosphatase and aryl hydrocarbon hydroxylase activities were lower by 60 and 80%, respectively, in the highly proliferating hepatoma than in the liver. In contrast, glucose-6-phosphate dehydrogenase activity increased in the hepatoma. However, enzyme inducers, such as methylcholanthrene, hydrocortisone, and insulin, were able to enhance the activity of these enzymes in the liver but had no stimulating effect on the hepatoma.
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PMID:Biochemistry and enzyme induction in MC-29 virus-induced transplantable avian hepatoma. 17 98

Two experiments were conducted to investigate the relationship of energy source, age and glucose-6-phosphatase activity in the chick. In the first experiment liver glycogen and glucose-6-phosphatase were assayed in chicks of four age groups being fed either a high-fat or high-carbohydrate diet. It was observed that the feeding of the high-fat diet resulted in higher glucose-6-phosphatase activity and lower glycogen levels than did the feeding of the carbohydrate diet. Age was found to significantly influence enzyme activity. Both glucose-6-phosphatase and liver glycogen were found to be negatively correlated in the fat fed chicks. In the second experiment chicks were fed either a high-fat or high-carbohydrate diet for 28 days. Liver glucose-6-phosphatase activity was determined in representative samples of chicks from each group to establish basal levels. The diets were then reversed for a three-day period, after which the chicks were returned to their initial diets. Glucose-6-phosphatase was analysed at each step. Variation in enzyme activity in the chicks initially fed the high-fat diet could be attributed to differences in body weight. However, those chicks originally fed the carbohydrate diet did exhibit a true metabolic adaption when fed the high-fat diet.
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PMID:The effect of non-protein energy sources on the ability of the chick to synthesize glucose-6-phosphatase. 18 May 11

Levels of cytochrome P-450 and the activities of amino-pyrinedemethylase and p-nitrophenol-UDP-glucuronyltransferase were measured in homogenates and microsomes of 16 to 19 day old chicken embryos exposed in ovo to phenobarbital. The activities of glucose-6-phosphatase were measured on the 19th day of incubation. After the highest dose of 3 X 8 mg phenobarbital, cytochrome P-450 increased 3-6fold, aminopyrinedemethylase activity 7fold and the activity of p-nitrophenol-UDP-glucuronyltransferase 3fold. Glucose-6-phosphatase activity was not increased but decreased. Corresponding to the given dose of phenobarbital (3X3, 3X4, 3X6, 3X8 mg) into the yolk sac an increase in enzyme activity levels mentioned above could as a rule be demonstrated at the level of p less than 0.0025. Calculated microsomal protein amounted to 43.0+/-6.5 mg/g liver.
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PMID:[Dose-dependent effects on phenobarbital on microsomal liver enzymes of chicken embryos (author's transl)]. 19 20

Methods were devised or modified which made it possible to measure phosphoenolpyruvate carboxykinase, fructose-1,6-bisphosphatase, and glucose-6-phosphatase in seven defined parts of single nephrons and in patches from thin limb and papilla areas dissected from freeze-dried microtome sections of rat kidney. All three enzymes were essentially confined to the proximal tubule. In normal kidneys, the levels were highest in the proximal convoluted tubule. Glucose-6-phosphatase was 20 times higher in the early part of the convoluted segment than in the late part of the straight segment. With one exception, in acidosis, only phosphoenolpyruvate carboxykinase increased (fourfold in the proximal convoluted segment but much less in the straight portion). In starvation, phosphoenolpyruvate carboxykinase increased about as much as in acidosis in the proximal straight tubule, but not as much in convoluted portions, whereas glucose-6-phosphatase rose modestly in both parts of the proximal tubule and fructose bisphosphatase rose only in the straight tubule, especially the early segment. It is suggested that ammoniagenesis can accompany gluconeogenesis in the proximal convoluted tubule but not in the straight segment.
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PMID:Distribution along the rat nephron of three enzymes of gluconeogenesis in acidosis and starvation. 21 58

Activities of the 4 hepatic gluconeogenic enzymes: glucose-6-phosphatase, fructose-1,6-diphosphatase, pyruvate carboxylase, particulate and cytosolic phosphoenolpyruvate carboxykinase (PEPCK) have been measured in fetal rabbits (22, 25, 28, 30 and 31 days of gestation) and in fasted or suckling newborns (1 and 2 days after birth). Between days 25 and 31 of gestation, fructose 1,6-diphosphatase and particulate PEPCK activities represent 50% of adult (pregnant female) activities, while pyruvate carboxylase is present at adult values during the same period. Glucose-6-phosphatase is low and cytosolic PEPCK absent in fetal liver until 30 days of gestation and increase significantly during the day preceding birth. Al the enzymes show a further increase after birth independently of the nutritional status of the animals (starved or suckling).
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PMID:Perinatal development of glucoeneogenic enzymes in rabbit liver. 22 57

The classical features of Type I glycogen storage disease (McKusick 23220) (GSD) are hepatomegaly, hypoglycaemia, and acidosis, enlargement of the kidneys and short stature. Glucose-6-phosphatase (EC 3.1.3.9) activity is defective not only in liver and kidney but also in small intestine (Field et al., 1965). In addition to the classical features, many patients suffer from episodes of diarrhoea (Fine et al., 1969). At the Hospital for Sick Children, Great Ormond Street, patients with the commoner forms of hepatic glycogen storage disease have episodes of diarrhoea or loose stools more commonly than was suspected. We have investigated small intestinal function in three patients with Type I GSD by both in vitro and in vivo techniques.
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PMID:Disordered intestinal function in glycogen storage disease. 22 44


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