Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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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 properties of fructose-1.6-disphosphatase in supernatant of homogenate of liver, kidneys, and adductor muscles of cattle were tested. EDTA was found to activate the enzyme up to concentrations of 10 mMol. The pH optimum was 7.5 in the presence of EDTA. Even lower concentrations of magnesium ions caused activation of the enzyme, but an activating effect was obtained as well from relatively high Mg concentrations. Fructose-1.6-diphosphatase could by activated also by 0.2 mMol Mn or Co ions or 1 mMol Zn ions. Inhibitive action was obtained from Cu, Cd, Pb, and Hg ions. Microsomal fractions of cattle liver and kidney caused high activity of glucose-6-phosphatase, but only low action was obtained be using microsomal fractions of mesenteric mucous membrane or brain. Mg ions, basically, failed to trigger activation, and higher concentrations even caused inhibition. The relatively high activity of both fructose-1.6-diphosphatase and glucose-6-phosphatase in kidney of cattle appeared to suggest an involvement of those enzymes in gluconeogenesis.
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PMID:[Mg dependence and other properties of fructose-1, 6-diphosphatase and glucose-6-phosphatase in various organs of cattle]. 0 44

Studies of the thermal stability of rat liver glucose-6-phosphatase (EC 3.1.3.9) were carried out to further elevate the proposal that the enzymic activity is the result of the coupling of a glucose-6-P-specific translocase and a nonspecific phosphohydrolase-phosphotransferase. Inactivation was observed when micorsomes were incubated at mild temperatures between pH 6.2 and 5.6. The rate of inactivation increased either with increasing hydrogen ion concentration or temperature. However, no inactivation was seen below 15 degrees in media as low as pH 5 or at neutral pH up to 37 degrees. The thermal stability of the enzyme may be controlled by the physical state of the membrane lipids and the degree of protonation of specific residues in the enzyme protein. Microsomes were exposed to inactivating conditions, and kinetic analyses were made of the glucose-6-P phosphohydrolase activities before and after supplementation to 0.4% sodium taurocholate. The results support the postulate and the kinetic characteristics of a given preparation of intact microsomes are determined by the relative capacities of the transport and catalytic components. Before detergent treatment, inactivation (i.e. a decrease in Vmax) was accompanied by a decrease in Km and a reduction in the fraction of latent activity, whereas only Vmax was depressed in disrupted preparations. The possibility that the inactivating treatments caused concurrent disruption of the microsomal membrane was ruled out. It is concluded that exposures to mild heat in acidic media selectively inactivate the catalytic component of the glucose-6-phosphatase system while preserving an intact permeability barrier and a functional glucose-6-P transport system. Analyses of kinetic data obtained in the present and earlier studies revealed several fundamental mathematical relationships among the kinetic constants describing the glucose-6-P phosphohydrolase activities of intact (i.e. the "system") and disrupted microsomes (i.e. the catalytic component). The quantitative relationships appear to provide a means to calculate a velocity constant (VT) and a half-saturation constant (KT) for glucose-6-P influx. The well documented, differential responses of the rat liver glucose-6-phosphatase system induced by starvation, experimental diabetes, or cortisol administration were analyzed in terms of these relationships. The possible influences of cisternal inorganic phosphate on the apparent kinetic constants of the intact system are discussed.
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PMID:Quantitative aspects of relationship between glucose 6-phosphate transport and hydrolysis for liver microsomal glucose-6-phosphatase system. Selective thermal inactivation of catalytic component in situ at acid pH. 1 Mar 5

Plasma membranes were isolated from the livers of control and Streptococcus pneumoniae-infected rats. This work, therefore, represents the first isolation of plasma membranes from infected actron microscopy and by the use of enzyme markers for microsomes (glucose-6-phosphatase), mitochondria (glutamate and malate dehydrogenases), and lysosomes (acid phosphatase). Plasma membranes from infected cells banded at the same sucrose density as plasma membranes from uninfected cells. Moreover, equivalent amounts of plasma membranes could be isolated from control and infected rat livers. There were, however, significant alterations in the enzyme complement of the plasma membrane after infection. 5'-Nucleotidase activity was significantly decreased, whereas alkaline phosphatase activity was significantly increased. Kinetic analysis demonstrated that only the Vmax and not the Km of these two enzymes was changed, suggesting that the altered affinity of the enzymes for substrate was not the mechanism responsible for the observed alterations. No change in the mitochondrial enzyme markers was observed after infection, but the specific activity of microsomal glucose-6-phosphatase decreased significantly. Possible explanations for the observed alterations are discussed.
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PMID:Isolation and partial characterization of plasma membranes from the livers of control and Streptococcus pneumoniae-infected rats. 1 27

Lysophosphatidylcholine acyltransferase, which catalyzes the acylation of lysophosphatidylcholine with fatty acid coenzyme A to form phosphatidylcholine, was assayed in gall-bladder mucosa. In guinea pig gall-bladder the activity parallels that of the microsomal enzyme, glucose-6-phosphatase with 3--4-fold enrichment of the activity in the microsomes. Studies with saturated and unsaturated substrates demonstrated highest activity when oleoyl coenzyme A and palmitoyl lysophosphatidylcholine were used and the lowest activity when palmitoyl coenzyme A and palmitoyl lysophosphatidylcholine were used. This activity was demonstrated in the dog, rabbit, cat, calf and human gall-bladder mucosa; however, a wide variation in the amount was observed. Lysophospholipase, which catalyzes the hydrolysis of lysophosphatidylcholine to glycerophosphorylcholine and fatty acid, was also demonstrated in gall-bladder mucosa.
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PMID:Lipid metabolism by The gall-bladder. II. The in vitro conversion of lysophosphatidylcholine to phosphatidylcholine. 2 25

Intraperitoneal administration of diazepame and phenazepame into rats /at a dose 50 mg/kg/ within 4 days did not induce liver microsomal enzymes. After administration of chlordiazepoxide at the same dose content of cytochrome P-450 was increased and the rate of dimethylaniline demethylation was elevated. Content of protein as well as NADPH-cytochrome-c-reductase and glucose-6-phosphatase activities were increased after intraperitoneal administration of all the preparations at a dose 100 mg/kg within 4 days. Experiments on the potentiation of hexenal effect demonstrated the decrease in the time of sleep in animals, treated with chlordiazepoxide at a dose 100 mg/kg of body weight.
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PMID:[Effect of 1,4-benzodiazepine tranquilizers on the activity of the hepatocyte hydroxylating complex and glucose-6-phosphatase in white rats]. 4 17

In experiments with albino rats it was found that after administration of phytobacteriomycin, trichotecin, hygromycin B or levoristatin into the stomach in doses of 1/20 of LD50 activity of the microsomal enzymes of the liver cells significantly changed and the changes persisted within at least 2 weeks. The above antibiotics induced similar changes in the lysosome enzyme, i.e. acid phosphatase, providing an increase in its activity. Changes in the activity of succinate dehydrogenase (mytochondria indicator enzyme), glucose-6-phosphatase (ribosome indicator enzyme) and aspartate aminotransferase (cytoplasm indicator enzyme) were different for each antibiotic. It is concluded that the above antibiotics were capable of impairing on intoxication the enzymatic function of various cell microstructures, though the levels of the change direction may be different.
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PMID:[Effect of phytobacteriomycin, trichotecin, hygromycin B and levoristatin on some rat liver enzymes]. 5 75

The acute effects of the PCB (polychlorinated biphenyls) mixture (Aroclor 1254) on microsomal enzymes and on synthesis and turnover of microsomal and cytoplasmic lipids of rat liver were investigated. Six daily i.p. injections of 25 and 50 mg PCB/kg body weight resulted in increased liver weight and liver to body weight ratios. When compared to controls PCB treatment resulted in a six-fold increase in amount of cytochrome P-450. Activities of NADPH-cytochrome c reductase, ethylmorphine demethylase and inosine diphosphatase were increased whereas glucose-6-phosphatase values were decreased by PCB exposure. Analysis of liver homogenate and microsomal fraction revealed an increase in lipid in PCB-exposed animals. Phospholipids, cholesterol and triglyceride were significantly increased after PCB exposure; however, the greatest percentage increase was seen in the triglyceride pool. The finding of an increase in microsomal triglyceride to phospholipid ratios with exposure to PCB is suggestive of an increase in membrane-enclosed lipid (liposomes). Studies with labelled glycerol indicated that the PCB-induced fatty liver resulted from increased half life but not increased synthesis of liver lipid moieties. The rate of incorporation of leucine into microsomal membrane and albumin was somewhat enhanced in rats exposed to PCB indicative of increased protein synthesis. Morphological studies showed increased occurrence of lipid material, both in cytoplasmic droplets and within rough and smooth-surfaced endoplasmic reticulum. Proliferation of smooth endoplasmic reticulum and flattened Golgi cisternae with no secretion granules containing lipoprotein particles characterized the liver from animals exposed for 6 days. The increase in lipid within membranes of the endoplasmic reticulum together with the flattened Golgi lacking typical secretory vesicles indicates a defect in transport of lipoproteins from the endoplasmic reticulum to the Golgi apparatus and may be the cause of the PCB-induced fatty liver.
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PMID:Studies on the cellular toxicity of polychlorinated biphenyls (PCBs). I. Effect of PCBs on microsomal enzymes and on synthesis and turnover of microsomal and cytoplasmic lipids of rat liver- a morphological and biochemical study. 9 1

Unlike halogenated benzenes, trichlorophenols did not induce xenobiotic metabolism in the rat. 2,3,5-, 2,3,6-, 2,4,5-, and 2,4,6-Trichlorophenol at doses as high as 400 mg/kg p.o. daily for 14 days did not alter EPN detoxification. Only 2,4,5-trichlorophenol at the highest dose decreased microsomal NADPH-cytochrome c reductase activity and cytochrome P-450 content. In vitro, all 4 isomers inhibited EPN detoxification and the demethylation of p-nitroanisole. UDP-glucuronyltransferase was not altered in vivo and was only slightly inhibited in vitro by 2,3,5- and 2,4,5-trichlorophenol. The compounds were not hepatotoxic as assessed by measurement of hepatic glucose-6-phosphatase and serum sorbitol dehydrogenase.
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PMID:Effect of trichlorophenols on xenobiotic metabolism in the rat. 10 51

Male Sprague-Dawley rats consumed a diet to which 100 ppm of various polychlorinated biphenyl (PCB) mixtures (Aroclors 1248, 1254, and 1262) were added for one year. Rats were hepatectomized at 13, 26, and 52 weeks during feeding and at 13 weeks following the discontinuation of the PCB diets. The liver homogenates of these rats had an increase in protein and RNA on a DNA basis and an increase in lipid and a decrease in DNA on the liver weight basis. The hepatic microsomes from these livers also had an increase in protein and cytochrome P-450. The RNA/microsomal protein levels were decreased, and no marked alterations were recorded for the phospholipids and cholesterol on a microsomal protein basis. Increased enzymatic activity was recorded for N-demethylase and nitroreductase. However, the specific activity of glucose-6-phosphatase was decreased throughout the treatment period.
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PMID:Responses of rats exposed to polychlorinated biphenyls for fifty-two weeks. II. Compositional and enzymatic changes in the liver. 12 Jan 38

An alternative to previous methods (tissue chopper, frozen sections) for the ultrastructural demonstration of phosphatases is described. The present approach is based on a short vascular perfusion of rat liver with glutaraldehyde through the inferior caval vein, followed by vascular perfusion incubation with a medium containing the enzyme substrates. The effect of glutaraldehyde on three different types of phosphatases was investigated, namely a lysosomal enzyme (acid phosphatase) a tightly bound microsomal enzyme (G6Pase) and a loosely bound microsomal enzyme (IDPase). It is demonstrated that by perfusion with glutaraldehyde for three minutes good cellular morphology is obtained and that 50-60% of the initial activity of glucose-6-phosphatase, inosine-diphosphatase and acid phosphatase remains. The localization and deposition of G6Pase activity were distinct and observed throughout the endoplasmic reticulum and the nuclear envelope. For acid phosphatase, the reaction product was confined to various types of lysosomes including presumed autophagic vacuoles. No signs of enzyme diffusion were noted. The present approach seems to offer some advantages: it is simple and requires no extra equipment, penetration of the fixative and incubation enzyme medium is good, and finally freeze artifacts are avoided.
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PMID:Ultrastructural demonstration of phosphatases by perfusion fixation followed by perfusion incubation of rat liver. 16 67


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