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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)

A method is described for the incorporation of a microsomal rat liver fraction into polyacrylamide films without significant loss of its glucose-6-phosphatase activity. The enzymatic activity was completely lost when the films were prepared with ammonium persulfate as initiator of the polymerization as previously described for alkaline phosphatase, but modification of this method showed that about 90% of the glucose-6-phosphatase activity could be retained. The enzyme in the films prepared with the new method was completely inhibited by alloxan, HgCl2, and preincubation in 0.05 M acetate buffer (pH 5.0) at 37 degrees C, as determined biochemically. Similar results were obtained for the enzyme in films determined histochemically according to the lead method of Wachstein and Meisel. In this respect the behavior of the incorporated enzyme is similar to that in suspension. Films fixed with 1.5% glutaraldehyde showed rapid inactivation of glucose-6-phosphatase. There was good correlation between the biochemical and histochemical activity determined after fixation. A method to embed polyacrylamide films in Epon for electron-microscopical investigation is also described. Dimethyl sulfoxide was used as the dehydrating agent instead of ethanol/acetone.
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PMID:Cytochemical model system for microsomal rat liver glucose-6-phosphate. 18 Jan 74

We describe a novel technique for the histochemical and cytochemical demonstration of glucose-6-phosphatase activity. In this method, lead is replaced by cobalt. After activity of glucose-6-phosphatase, cobalt phosphate Co3(PO4)2 is formed, and in the presence of ammonium sulfide (NH4)2S, the precipitate is transformed into a sulfide that fixes osmium and provides good electron density. Glucose-6-phosphatase activity was determined mostly in rat kidney cells, but controls were also performed in liver cells. A strong reaction was seen in proximal tubule cells, but the reaction was weak in distal convoluted tubule cells. This technique showed the same endoplasmic reticulum (ER) organization in proximal and distal nephron as that seen with the osmium impregnation technique. In collecting tubules, intercalated cells had irregular reactivity, while principal cells had none. Our results indicate that the cobalt technique is valid, reliable, and sensitive enough to detect low glucose-6-phosphatase activity. Moreover, the technique can be used with 1-mm-thick specimens and obviates the need for use of frozen tissue sections.
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PMID:A new method based on cobalt for histochemical and cytochemical demonstration of glucose-6-phosphatase activity. 216 94

Experiments were done on rats to investigate the nature of the renal response to metabolic acidosis and the changes in enzyme activity associated with increased ammoniagenesis. When metabolic acidosis was induced with oral feeding of ammonium chloride for 48 hr, there was an increase of activity of the enzyme phosphoenolpyruvate carboxykinase (PEPCK) in whole kidneys as well as in the kidney cortex. There was no change in PEPCK in liver, and glucose-6-phosphatase showed no change in kidney or liver in response to metabolic acidosis. The increase in PEPCK activity in kidney cortex varied with the degree of acidosis and there was a close correlation between cortical PEPCK activity and urinary ammonia. Kidney cortex mitochondrial PEPCK did not change in response to metabolic acidosis. An increase in PEPCK occurred as early as 6 hr after NH(4)Cl feeding, before there was any increase in kidney glutaminase I activity. Rats fed sodium phosphate, or given triamcinolone intramuscularly, developed a metabolic alkalosis, but there was increased urinary ammonia and an increase in activity of renal cortical PEPCK. Triamcinolone plus ammonium chloride induced a greater increase of PEPCK activity than triamcinolone by itself; on the contrary, the rise of glucose-6-phosphatase induced by triamcinolone was not enhanced by acidosis. Glucose-6-phosphatase from control and acidotic rats had identical kinetic characteristics. The results indicate that increased PEPCK activity is constantly related to increases of urinary ammonia. It is proposed that the increase of PEPCK activity is the key event in the ammoniagenesis and gluconeogenesis which follow on metabolic acidosis.
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PMID:Renal metabolic response to acid base changes. I. Enzymatic control of ammoniagenesis in the rat. 430 57

The kinetics of the induction of rat kidney phosphoenolpyruvate carboxykinase activity after triamcinolone and ammonium chloride administration have been investigated with a view to the further differentiation of the two processes. The half-life of kidney phosphoenolpyruvate carboxykinase activity, as measured from the decay curve after a single doses of triamcinolone, is approximately 1.4 hr. This compares with a half-life for the enzyme from acidotic kidney of approximately 3.4 hr. Analysis of the data indicates that the induction of phosphoenolpyruvate carboxykinase activity by triamcinolone may be attributed to an increase in de novo protein synthesis. Induction by acidosis is qualitatively distinct and is partly attributed to a reduction in the rate of decay of phosphoenolpyruvate carboxykinase activity. The activities of the gluconeogenic enzymes glucose-6-phosphatase, fructose-1,6-diphosphatase, and phosphoenolpyruvate carboxykinase in both liver and kidney have been measured in animals separately treated with triamcinolone and ammonium chloride. Triamcinolone significantly increases the activities of liver phosphoenolpyruvate carboxykinase, kidney glucose-6-phosphatase, and kidney phosphoenolpyruvate carboxykinase only; ammonium chloride stimulates a 200% increase in kidney phosphoenolpyruvate carboxykinase, but has no effect on the other enzymes. The induction processes whereby triamcinolone increases phosphoenolpyruvate carboxykinase activities in liver and kidney differ quantitatively.
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PMID:The effect of steroids and ammonium chloride acidosis on phosphoenolpyruvate carboxykinase in rat kidney cortex. II. The kinetics of enzyme induction. 434 28

Five min after administration of a single, i.p. dose of ammonium metavanadate (5 mg/kg), in rats, liver enzyme activities were measured. Microsomal mixed-function oxidases (except for aminopyrine N-demethylase), glucose-6-phosphatase and alkaline phosphatase were inhibited but lactate, malate, and glycerophosphate dehydrogenases as well as microsomal NADPH2-dependent cytochrome c reductase were unchanged.
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PMID:Effects of ammonium metavanadate on rat liver enzymes. 660 66

Chronic oral administration of ammonium molybdate in rats markedly retarded the growth rate of rats and high protein diet could partially reverse this condition. The activities of several enzymes viz. acid phosphatase, alkaline phosphatase, glucose-6-phosphatase, succinic dehydrogenase, glutamate oxaloacetate transaminase, inorganic pyrophosphatase and acetylcholinesterase in different tissues and serum levels of luteinizing hormone, follicle stimulating hormone, prolactin and cortisol are altered due to the toxicity conditions and high protein diet fed group of animals showed almost normal values in respect of a few of these parameters. Normal histological pattern of both liver and kidney tissues were altered under molybdenum toxicity condition. Significant increase of basophilic substances are observed in the cytoplasm of the liver cells of the toxic group of animals which is counteracted by feeding high protein diet.
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PMID:Biochemical studies on molybdenum toxicity in rats: effects of high protein feeding. 732 62

The probable involvement of hepatic carbamyl-P in the reciprocal relationship between hepatic ureagenesis and glycogenesis from glucose was explored. Isolated perfused liver preparations from 48-h fasted rats were employed. Moderate (9.2 mM) and relatively high levels of glucose (34 mM) were perfused. Hepatic glycogenesis, glucose-6-P, carbamyl-P, and citrulline levels, hepatic urea formation, and ureagenesis based upon perfusate urea levels were measured. Experimental probes selected to modify hepatic ureagenesis and carbamyl-P production and utilization included: (a) NH4Cl, maintained at 5 mM by continuous infusion (NH4+ is a substrate for carbamyl-P synthase I and glutamate dehydrogenase); (b) norvaline, an inhibitor of ornithine transcarbamylase which catalyzes the first committed step in the urea cycle; and (c) ethoxyzolamide, an inhibitor of carbonic anhydrase which produces HCO3-, an essential substrate for carbamyl-P synthase I. NH4+ increased ureagenesis and decreased glycogenesis. The inclusion of norvaline with NH4+ decreased ureagenesis and increased glycogenesis. Ethoxyzolamide with or without NH4+ inhibited both ureagenesis and glycogenesis, and decreased the hepatic glucose-6-P level. Glycogenesis was greater at 34 mM than 9.2 mM glucose, increased in norvaline-containing preparations correlative with increased availability of carbamyl-P, and decreased when carbamyl-P formation was inhibited by ethoxyzolamide. Kinetic analysis indicated a Km, Glc of 31 mM for glucose phosphorylation preliminary to glycogenesis. Glycogen formation via the "indirect pathway" (i.e. involving extrahepatic glycolysis, transport of lactate to the liver, and glyconeogenesis therefrom) was quantitatively insufficient to account for the observed glycogenesis. Glucokinase is contraindicated by the inverse relationship between hepatic glycogenesis and ATP availability in the ethoxyzolamide-treated preparations. In contrast, carbamyl-P:glucose phosphotransferase activity of the glucose-6-phosphatase system has the characteristics to bridge hepatic ureagenesis and glycogenesis.
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PMID:Glycogenesis from glucose and ureagenesis in isolated perfused rat livers. Influence of ammonium ion, norvaline, and ethoxyzolamide. 813 5

The histocytochemical method for the detection of glucose-6-phosphatase activity has been studied in the rat heart tissue by using cobalt-capture technique. The incubation medium had the following ingredients: cobalt chloride, PIPES-NaOH buffer pH = 6.7, glucose-6-phosphate disodium salt and phenylalanine. Cobalt was revealed by using a solution of 1% ammonium sulfide and was fixed by osmium tetroxide. The most effective concentration of cobalt chloride was 50 mM. With a concentration lower than 30 mM, the reaction products were not determined. With a higher concentration, a small non-specific precipitation was visualized. Ultracytochemically, a strong enzyme reaction was present in the nuclear envelopes of cardiac myocytes, endotheliocytes and in the sarcoplasmic reticulum. These results imply that the method used is valid and can be recommended for studying the localization of glucose-6-phosphatase activity.
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PMID:Localization of glucose-6-phosphatase activity in the rat cardiac muscle by cobalt-based cytochemistry. 813 99

In rats injected with bacterial lipopolysaccharide (LPS; 5 gamma mg/g body weight [BWT]), the toxin provokes death within 24 h in 23% of the animals and, in surviving rats, causes a decrease in BWT, hyperlactacidemia, hyperlipacidemia, and hyperketonemia, as well as depletion of both liver and muscle glycogen content. In the liver, LPS severely lowers the ATP and total adenine nucleotide content, ATP/ADP ratio, and adenylate charge. In hepatocytes from LPS-injected rats, the oxidation of D-glucose is first increased 2 h after administration of the toxin, despite close-to-normal phosphorylation of the hexose. In hepatocytes prepared from rats killed 24 h after injection of LPS, the phosphorylation of D-glucose, its incorporation into glycogen, and its oxidation are all severely impaired. This sequence of changes, which coincides with a decreased ratio between pyruvate and lactate production from exogenous D-glucose, is comparable to that found with agents that uncouple oxidative phosphorylation. The injection of LPS also alters the metabolic response of hepatocytes to the dimethyl ester of succinic acid (SAD), in terms, for instance, of the sparing action of the ester upon both the production of 14CO2 by hepatocytes prelabeled with L-[U-14C] glutamine and the output of NH4+, and its inhibitory action on glycogenolysis and futile cycling in the reactions catalyzed by glucokinase and glucose-6-phosphatase. Nevertheless, the infusion of SAD protects the rats against the deleterious effect of LPS upon such variables as the plasma concentration of free fatty acids and beta-hydroxybutyrate, the liver ATP content, and the oxidation of D-glucose, as well as the pyruvate/lactate ratio, in hepatocytes prepared from the LPS-injected rats. The infusion of SAD also virtually suppresses lethality in the LPS-injected animals. It is proposed, therefore, that the infusion of succinic acid esters may represent a novel therapeutic approach in endotoxemia and multiple-organ failure.
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PMID:Protective effects of succinic acid dimethyl ester infusion in experimental endotoxemia. 917 84

The effect of cyclosporin A, a highly effective immunosuppressant, was investigated on hyperoxaluric rats with and without vitamin E pretreatment. Hyperoxaluria was induced by oral feeding of 3% ammonium oxalate in water for 3 days. Cyclosporin A (50 mg/kg body wt.) was administered for 3 days. Pretreatment with vitamin E (50 mg/100 g body wt., once a week for 3 weeks) was carried out before the administration of cyclosporin A and ammonium oxalate. Nonenzymatic ascorbate-induced lipid peroxidation was increased to 1.55-fold in either cyclosporin A-administered or hyperoxaluric rat kidney and liver when compared to control. The lipid peroxidation was further elevated to 1.9-fold when both cyclosporin A and ammonium oxalate were coadministered. The activities of renal and hepatic ATPase, glucose-6-phosphatase as well as the concentrations of thiols were decreased significantly (p < 0.001) when cyclosporin A was administered under hyperoxaluric condition. On pretreatment with vitamin E the cyclosporin A-induced biochemical changes observed in the presence of hyperoxaluria were abolished.
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PMID:Effect of cyclosporin A on tissue lipid peroxidation and membrane bound phosphatases in hyperoxaluric rat and the protection by vitamin E pretreatment. 935 65


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