Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.3.9 (glucose-6-phosphatase)
 3,081 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

By means of a preparation technique based on the discontinuous sucrose density gradient, subcellular fractions were isolated from guinea pig intestinal smooth muscle cells. A fraction which distributed to a 33% sucrose layer showed relatively high activities of 5'-nucleotidase, Na+ . K+-ATPase and ouabain sensitive Na+ . K+-ATPase. The fraction had a low NaN3 sensitive Mg2+-ATPase activity. On the other hand, the high activity of glucose-6-phosphatase showed a broad distribution. Though the sucrose density gradient proceeded over a series of the fine layers, cross-contamination of microsome into the 33% sucrose fraction was not reduced. To reduce microsomal cross-contamination, another procedure was employed. The homogenization time of 77000 xg sediment to be layered on the top of the sucrose density gradients was prolonged. This procedure did not change the distribution of K+ activated p-nitrophenylphosphatase, K+ activated ouabain sensitive p-nitrophenylphosphatase and ouabain sensitive Na+ . K+-ATPase activities. The peak of NADH cytochrome c reductase activity was shifted to a 38% sucrose fraction from a 33% sucrose fraction and the activity of this marker enzyme in the 33% sucrose fraction decreased to 60% of that of the prior procedure.
 ...
PMID:[Examination of plasma membrane-enriched fraction from guinea pig intestinal smooth muscle by means of some marker enzymes (author's transl)]. 23 74

1. Glucose-6-phosphatase (EC 3.1.3.9 D-glucose-6-phosphate phosphohydrolase) was found to be localized mainly in the endoplasmic reticulum (microsomal fraction) of all species of vertebrate liver tissue examined. 2. Hepatopancreas tissue from gastropod molluscs was found to be unique in showing the localization of glucose-6-phosphatase in the cytosol (soluble fraction).
 ...
PMID:Subcellular localization of glucose-6-phosphatase in animal tissues. 23 8

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.
 ...
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.
 ...
PMID:On the involvement of a glucose 6-phosphate transport system in the function of microsomal glucose 6-phosphatase. 23 36

The subcellular localization of guanylate cyclase was examined in rat liver. About 80% of the enzyme activity of homogenates was found in the soluble fraction. Particulate guanylate cyclase was localized in plasma membranes and microsomes. Crude nuclear and microsomal fractions were applied to discontinuous sucrose gradients, and the resulting fractions were examined for guanylate cyclase, various enzyme markers of cell components, and electron microscopy. Purified plasma membrane fractions obtained from either preparation had the highest specific activity of guanylate cyclase, 30 to 80 pmol/min/mg of protein, and the recovery and relative specific activity of guanylate cyclase paralleled that of 5'-nucleotidase and adenylate cyclase in these fractions. Significant amounts of guanylate cyclase, adenylate cyclase, 5'-nucleotidase, and glucose-6-phosphatase were recovered in purified preparation of microsomes. We cannot exclude the presence of guanylate cyclase in other cell components such as Golgi. The electron microscopic studies of fractions supported the biochemical studies with enzyme markers. Soluble guanylate cyclase had typical Michaelis-Menten kinetics with respect to GTP and had an apparent Km for GTP of 35 muM. Ca-2+ stimulated the soluble activity in the presence of low concentrations of Mn-2+. The properties of guanylate cyclase in plasma membranes and microsomes were similar except that Ca-2+ inhibited the activity associated with plasma membranes and had no effect on that of microsomes. Both particulate enzymes were allosteric in nature; double reciprocal plots of velocity versus GTP were not linear, and Hill coefficients for preparations of plasma membranes and microsomes were calculated to be 1.60 and 1.58, respectively. The soluble and particulate enzymes were inhibited by ATP, and inhibition of the soluble enzyme was slightly greater. While Mg-2+ was less effective than Mn-2+ as a sole cation, all enzyme fractions were markedly stimulated with Mg-2+ in the presence of a low concentration of Mn-2+. Triton X-100 increased the activity of particulate fractions about 3- to 10-fold and increased the soluble activity 50 to 100%.
 ...
PMID:Localization of particulate guanylate cyclase in plasma membranes and microsomes of rat liver. 23 12

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.
 ...
PMID:Membrane effects on hepatic microsomal glucose-6-phosphatase. 24 94

The inducing effect of certain barbiturates (secobarbitone, thiopentone, pentobarbitone, allobarbitone, phenobarbitone and barbitone) on the levels of the hepatic microsomal drug-metabolizing enzymes has been studied in the rat both in vivo and in vitro. The extent of induction was related to the plasma half-lives of the barbiturates; compounds with low rates of metabolism and long half-lives were the most potent inducing agents. The latter (phenobarbitone, pentobarbitone and allobarbitone) were shown by spectral technique to interact with cytochrome P-450 suggesting that their mechanism of enzyme induction was 'substrate induction' in type. Barbiturates containing an allyl group (secobarbitone and allobarbitone) had a weaker inducing effect than expected, possibly due to their destruction of cytochrome P-450. Despite its short plasma half-life of 0-5 h thiopentone was a relatively potent inducer probably due to its metabolism to pentobarbitone, which has a much longer plasma half-life (1-3 h). Barbitone is an effective inducer of the drug-metabolizing enzymes, yet does not interact spectrally with cytochrome P-450; this is in accord with the observations that although there are increases in NADPH-cytochrome c reductase and cytochrome b5, following administration of barbitone there is no increase in cytochrome P-450. Barbiturate pretreatment does not affect the activities of glucose-6-phosphatase, glucose-6-phosphate dehydrogenase or 6-phosphogluconate dehydrogenase.
 ...
PMID:Mechanism of induction of hepatic microsomal drug metabolizing enzymes by a series of barbiturates. 24 86

Primary monolayer culture of adult rat hepatocytes represents a novel and potentially useful technique to study many aspects of hepatic physiology for extended periods of time in vitro (J Cell Biol 59:722-734, 1973). In examining the hepatic drug-metabolizing system in these cells, we have discovered that the conditions of cell culture exert rapid, selective, and reproducible changes in microsomal enzymes. In the 24- to 48-hr period immediately following preparation and culture of the isolated parenchymal cells, the level of the drug-binding microsomal hemoprotein, cytochrome P-450, measured in extracts of cell homogenates, declined to less than 20% of its in vivo level, whereas NADPH-cytochrome c reductase activity was only moderately reduced and glucose-6-phosphatase activity remained unchanged. The activity of aminopyrine-N-demethylase and aniline hydroxylase also fell, paralleling the level of cytochrome P-450. By contrast, p-nitroanisole O-demethylase activity was unchanged in the cultured hepatocytes despite evidence (type I binding spectrum, NADPH requirement, inhibition by carbon monoxide or by SKF 525A) that p-nitroanisole O-demethylase is a cytochrome P-450-dependent enzyme. In culture, as in vivo, aromatic polycyclic hydrocarbons stimulated p-nitroanisole O-demethylase and aryl hydrocarbon (benzo [a] pyrene) hydroxylase activities; however, this effect was unaccompanied by a detectable increase in total carbon monoxide-binding hemoprotein. The data indicate that the profile of microsomal oxidase enzymes and their control undergo striking changes as hepatocytes adapt to cell culture.
 ...
PMID:Drug metabolism in adult rat hepatocytes in primary monolayer culture. 40 8

A liver perfusion system was assembled and adapted for pulse labelling studies. The perfusion medium was prepared by emulsifying perfluorotributylamine and Pluronic F 68 in a CO2 atmosphere using a sonicator. Ribosome-rich and ribosome-poor rough microsomes, smooth microsomes and Golgi membranes could be prepared from perfused livers with a good purity and recovery as from non-perfused livers. The subfractionation technique used was simple and involved slight modifications of the methods described earlier by Eriksson (1973) and Ehrenreich et al. (1973). The specific activity of NADPH-cytochrome c reductase in microsomes and of UDP-galactosyltransferase in Golgi membranes from perfused and non-perfused livers were identical. The specific activity of glucose-6-phosphatase in microsomes was slightly decreased after perfusion, but the membrane permeability barrier to glucose-6-phosphate remained intact. The granulated microsomal fractions from perfused liver had a somewhat reduced number of membrane-bound ribosomes. The system developed proved useful in studies of the synthesis and intracellular transport of albumin. The technique should also be suitable for use in studies of membrane biogenesis.
 ...
PMID:The study of biogenetic pathways using a perfusion technique containing perfluorochemicals. 44 22

The effect of postdecapitative ischemia (5 min at 37 degrees) and hypoxia (5% O2, 95% N2, 30 min) on the distribution of protein radioactivity in the cellular fractions of guinea pig cerebral cortex was studied. Ischemic conditions resulted in the increase of total radioactivity level and protein content in the mitochondrial fraction. In the cytosol the opposite effect was observed; the radioactivity and protein content were decreased. The amino acid analysis of microsomal proteins and the distribution of glucose-6-phosphatase activity, differing from those in control animals, suggest structural disturbances in the microsomal fraction. The results indicate a different sedimentation of proteins in the given experimental conditions. After hypoxia such effects were not observed.
 ...
PMID:Effect of hypoxia and ischemia on the distribution of protein in brain cellular fractions. 45 Jan 70


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>