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At least 253 records · Page 14Linked to original sources
PubMed1987

Alterations in the activities of rat tissue hexose monophosphate dehydrogenases in response to premature weaning and dietary restriction at mid-lactation.

The activities of the hexose monophosphate dehydrogenases increased in adipose tissue, remained unchanged in liver and decreased in mammary gland following the weaning of rats at mid-lactation (day 14). When dietary intake was restricted at mid-lactation, the activities of the hexose monophosphate dehydrogenases increased in adipose tissue, decreased in liver, but were unaltered in mammary gland. Premature weaning on day 14 postpartum resulted in maternal increases in both plasma insulin and glucose, which peaked at day 16. The plasma insulin levels decreased from day 14 to day 18 postpartum in the normal lactating rat, and a similar trend was observed for animals on a restricted dietary intake. Daily food consumption in the lactating rat decreased from 50 g to 20 g after premature weaning. The live weight of pups raised on dams given a restricted food intake from day 14 had decreased by day 17 postpartum, whereas an increase in daily live weight gain was recorded for the litters from the lactating controls. The results demonstrate that the activities of the hexose monophosphate dehydrogenases are regulated differentially between tissues of the lactating rat.

Adipose Tissue↗
PubMed1988

Comparative studies on the glycolytic and hexose monophosphate pathways in Candida parapsilosis and Saccharomyces cerevisiae.

Some enzymatic activities of the glycolytic and hexose monophosphate pathways of Candida parapsilosis, a yeast lacking alcohol dehydrogenase but able to grow on high glucose concentrations, were compared to those of Saccharomyces cerevisiae. Cells were grown either on 8% glucose or on 2% glycerol and activities measured under optimal conditions. Results were as follows: glycolytic enzymes of C. parapsilosis, except glyceraldehyde 3-phosphate dehydrogenase, exhibited an activity weaker than that of S. cerevisiae, especially when yeasts were grown on glycerol. Fructose-1,6 bisphosphatase, an enzyme implicated in gluconeogenesis and in the hexose monophosphate pathway, and known to be very sensitive to catabolite repression in S. cerevisiae, was always active in C. parapsilosis even when cells were grown on 8% glucose. However, the allosteric properties towards AMP and fructose-2,6-bisphosphate were the same in both strains. Glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, two other enzymes of the hexose monophosphate pathway, exhibited a higher activity in C. parapsilosis than in S. cerevisiae. Regulation of two important control points of the glycolytic flux, phosphofructokinase and pyruvate kinase, was investigated. In C. parapsilosis phosphofructokinase was poorly sensitive to ATP but fructose-2,6-bisphosphate completely relieved the light ATP inhibition. Pyruvate kinase did not require fructose-1,6-bisphosphate for its activity, and by this way, did not regulate the glycolytic flux.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1985

Regulation of expression of the sodium-coupled hexose transporter in cultured LLC-PK1 epithelia.

A variety of techniques have been used to study the sodium-coupled hexose transporter in epithelia formed by LLC-PK1 cells. The expression of the transporter is affected by the density and age of the culture and by the concentration of glucose in the growth medium. Sodium-coupled hexose transport appears as the epithelium becomes confluent and increases further as the epithelium matures. The increased transport is associated with increased transport in apical plasma membrane vesicles. Epithelia grown in medium containing 5 mM glucose express more transporters than epithelia grown in medium containing 25 mM glucose. The increase in transport is not the result of an extracellular signal that is generated as a consequence of the concentration of glucose. The response to different hexoses that are or are not transported on the carrier indicates that it is the metabolism of glucose that acts as the signal for expression of more or fewer transporters. The results are compared to similar studies of the effects of substrate concentration on expression of transporters in cultured fibroblasts and the intestines in situ.

Animals↗
PubMed2001

Fructose 2,6-bisphosphate activates pyrophosphate: fructose-6-phosphate 1-phosphotransferase and increases triose phosphate to hexose phosphate cycling in heterotrophic cells.

The aim of this work was to establish the influence of fructose 2,6-bisphosphate (Fru-2,6-P2) on non-photosynthetic carbohydrate metabolism in plants. Heterotrophic callus lines exhibiting elevated levels of Fru-2,6-P2 were generated from transgenic tobacco (Nicotiana tabacum L.) plants expressing a modified rat liver 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase. Lines containing increased amounts of Fru-2,6-P2 had lower levels of hexose phosphates and higher levels of 3-phosphoglycerate than the untransformed control cultures. There was also a greater redistribution of label into the C6 position of sucrose and fructose, following incubation with [1-13C]glucose, in the lines possessing the highest amounts of Fru-2,6-P2, indicating a greater re-synthesis of hexose phosphates from triose phosphates in these lines. Despite these changes, there were no marked differences between lines in the metabolism of 14C-substrates, the rate of oxygen uptake, carbohydrate accumulation or nucleotide pool sizes. These data provide direct evidence that physiologically relevant changes in the level of Fru-2,6-P2 can affect pyrophosphate: fructose-6-phosphate 1-phosphotransferase (PFP) activity in vivo, and are consistent with PFP operating in a net glycolytic direction in the heterotrophic culture. However, the results also show that activating PFP has little direct effect on heterotrophic carbohydrate metabolism beyond increasing the rate of cycling between hexose phosphates and triose phosphates.

Animals↗
PubMed1979

The effect of intracellular pH on the rate of hexose uptake in Chlorella.

The rate of hexose uptake by Chlorella is reduced by uncouplers such as carbonyl cyanide p-trifluoromethoxyphenyl hydrazone or dinitrophenol even before concentration equilibrium is reached. The addition of uncouplers changes the membrane potential and the intracellular pH. The membrane potential does not influence the initial velocity of net sugar uptake, whereas manipulation of the cell pH by means of dimethyloxazolidinedione or by butyric acid uncovered a dramatic influence of cell pH on the rate of hexose uptake: at pH values of 7.5--6.8 maximal rate of uptake is observed but at more acid pH a strong inhibition takes place with virtually total blockage of uptake at pH 6.1. The decrease of cell pH to 6.1 in the presence of carbonyl cyanide p-trifluoromethoxyphenyl hydrazone could therefore account for the decrease in hexose transport rate. It was shown that the intracellular pH as such determines the rate of uptake and not the pH difference between inside and outside; the transport rate did not correlate with delta pH.

Biological Transport↗
PubMed1988

Direct interaction of phenylarsine oxide with hexose transporters in isolated rat adipocytes.

It has previously been shown that phenylarsine oxide (PhAsO), an inhibitor of protein internalization, also inhibits stereospecific uptake of D-glucose and 2-deoxyglucose in both basal and insulin-stimulated rat adipocytes. This inhibition of hexose uptake was found to be dose-dependent. PhAsO rapidly inhibited sugar transport into insulin-stimulated adipocytes, but at low concentrations inhibition was transient. Low doses of PhAsO (1 microM) transiently inhibit stereospecific hexose uptake and near total (approx. 90%) recovery of transport activity occurs within 20 min. Interestingly, once recovered, the adipocytes can again undergo rapid inhibition and recovery of transport activity upon further treatment with PhAsO (1 microM). In addition, PhAsO is shown to inhibit cytochalasin B binding to plasma membranes from insulin-stimulated adipocytes in a concentration-dependent manner which parallels the dose-response inhibition of hexose transport by PhAsO. The data presented suggest a direct interaction between the D-glucose transporter and PhAsO, resulting in inhibition of transport. The results are consistent with the current recruitment hypothesis of insulin activation of sugar transport and indicate that a considerable reserve of intracellular glucose carriers exists within fat cells.

Adipose Tissue↗
PubMed1996

Effect of metformin on SGLT1, GLUT2, and GLUT5 hexose transporter gene expression in small intestine from rats.

The effect of the antihyperglycaemic agent metformin was studied on gene expression of the energy-dependent sodium-hexose cotransporter (SGLT1) and the facilitative hexose transporters GLUT2 and GLUT5 in rat intestine. Metformin treatment (125 mg/kg body wt. twice daily for a period of 3 days) significantly increased SGLT1 gene expression in duodenum and jejunum. GLUT5 gene expression was increased by metformin treatment only in the jejunum. Gene expression of GLUT2 in the intestine was not significantly affected by metformin treatment. This increase in transporter gene expression offers the potential for increases in hexose uptake at the brush border membrane, and may compensate for other effects of the drug that have been suggested to decrease glucose uptake by SGLT1, as well as for metformin stimulation of glucose utilization by the intestinal mucosa.

Animals↗
PubMed1992

A potential hexose transporter gene expressed predominantly in the bloodstream form of Trypanosoma brucei.

A cDNA cloned from Trypanosoma brucei brucei codes for a putative membrane protein which is homologous to the erythrocyte glucose transporter and several other sugar transporters from Escherichia coli, yeast, algae and Leishmania. This cDNA hybridizes to a 2.3-kb mRNA that accumulates to a much higher degree in the bloodstream mammalian form than in the procyclic insect form of the parasite. The correlation between the expression of this gene and the hexose metabolism of Leishmania enriettii and T. brucei suggest that these 2 related genes probably encode hexose transporters. The gene encoding this mRNA is a member of a multigene family. The putative hexose transporter gene is highly conserved among Kinetoplastidae, indicating an important role for this protein in the parasite life cycle.

Amino Acid Sequence↗
PubMed1996

Release of fructose and hexose phosphates from perivascular cells induced by low density lipoprotein and acceleration of protein glycation in vitro.

We investigated whether low density lipoprotein (LDL) under oxidative stress might induce the release of fructose, glucose-6-phosphate and fructose-6-phosphate from perivascular cells, and also whether these substances might accelerate the formation of advanced glycation end products (AGE) from proteins in vitro. When vascular smooth muscle cells were incubated with LDL in Ham's F10 at 37 degrees C for 48 h. release of all these substances was increased dose-dependently by oxidized LDL. Fructose release was increased in a dose-dependent manner by glucose. Indomethacin (20 microM) significantly (P < 0.01) suppressed the release of fructose (25.4 +/- 15.7% of control) and hexose phosphates (29.4 +/- 4.0) with the inhibition of release of lactate dehydrogenase (35.5 +/- 4.9) as well as probucol, whereas an aldose reductase inhibitor, epalrestat, significantly (P < 0.001) inhibited only the fructose release (0.9 +/- 0.8). Release of fructose and hexose phosphates from vascular endothelial cells was also induced by oxidized LDL. AGE immunoreactivities and AGE-related fluorescence formed from proteins and glucose were significantly increased (P < 0.001) in the presence of small amounts of the cellular glucose metabolites (6.6%) with glucose (93.4%). These data suggest that release of potent AGE initiators, fructose and hexose phosphates, from perivascular cells induced by oxidized LDL may be an important phenomenon for vascular complications.

Aldehyde Reductase↗
PubMed1978

Distribution of adenosine 5'-triphosphate (ATP)-dependent hexose kinases in microorganisms.

A systematic study of adenosine triphosphate (ATP)-dependent hexose kinases among microorganisms has been undertaken. Sixteen hexose kinases of five major types were partially purified from 12 microorganisms and characterized with respect to specificity for sugar and nucleotide substrates and Michaelis constants for the sugar substrates. Glucokinase activities that phosphorylate glucose and glucosamine are inhibited by N-acetyl-glucosamine and xylose, were found to be present in the non-sulphur photosynthetic bacteria Rhodospirillum rubrum, the blue-green algae Anacystis montana, and the protists Chlorella pyrenoidosa and Chlamydomonas reinhardtii (green algae), Hypochytrium catenoides (Hypochytridiomycete) and Saprolegnia Iitoralis (Oomycete). The myxobacteria Stigmatella aurantiaca contains a glucokinase activity with a different specificity pattern. Anacystis and Chlorella, besides their glucokinase activities, contain highly specific fructokinases, although that from Anacystis can also phosphorylate fructosamine; fructokinase from Anacystis has a molecular weight of 20 000, and exhibits a sigmoidal saturation curve for ATP when the Mg2+/ATP ratio is 2; this curve is transformed to a Michaelian one when under the same conditions an excess of Mg2+ (5 mM) is added. Saprolegnia however, besides the glucokinase, contains a mannofructokinase activity that phosphorylates mannose (Km 0.06 mM) and fructose (1 mM). On the other hand, hexokinase, a low specificity enzyme, was detected in the protist Allomyces arbuscula (Chytridiomycete) and in fungi Mucor hiemalis and Phycomyces blakesleeanus (Zygomycetes), and Schizophyllum commune (Basidiomycete). Schizophyllum contains a glucomannokinase activity together with hexokinase activity. The pattern of distribution of ATP-dependent hexose kinases among microorganisms seems to parallel that reported for biosynthetic pathways for lysine. The correlation with other biochemical parameters is also considered.

Bacteria↗
PubMed2005

Analysis of Saccharomyces cerevisiae hexose carrier expression during wine fermentation: both low- and high-affinity Hxt transporters are expressed.

The transport of glucose and fructose into yeast cells is a critical step in the utilization of sugars during wine fermentation. Hexose uptake can be carried out by various Hxt carriers, each possessing distinct regulatory and transport-kinetic properties capable of influencing yeast fermentation capacity. We investigated the expression pattern of the hexose transporters Hxt1 to 7 at the promoter and protein levels in Saccharomyces cerevisiae during wine fermentation. The Hxt1p carrier was expressed only at the beginning of fermentation, and had no role during stationary phase. The Hxt3p carrier was the only one to be expressed throughout fermentation, displaying maximal expression at growth arrest and slowly decreasing in abundance over the course of the stationary phase. The high-affinity carriers Hxt6p and Hxt7p displayed similar expression profiles, with expression induced at entry into stationary phase and persisting throughout the phase. The expression of these two carriers occurred despite the presence of high amounts of hexoses, and the proteins were stably expressed when the cells were starved for nitrogen. The Hxt2p transporter was only transiently expressed during lag phase, which suggests a role for the protein in growth initiation. Characterization of glucose transport kinetics indicated the presence of a shift in the low-affinity component that is consistent with a predominant expression of Hxt1p during growth phase and of Hxt3p during stationary phase. In addition, a high-affinity uptake component consistent with functional expression of Hxt6p/Hxt7p was identified during stationary phase.

Culture Media↗
PubMed2003

Murine hexose-6-phosphate dehydrogenase: a bifunctional enzyme with broad substrate specificity and 6-phosphogluconolactonase activity.

Murine hexose-6-phosphate dehydrogenase has been purified from liver microsomes by affinity chromatography on 2('),5(')-ADP-Sepharose. The purified enzyme has 6-phosphogluconolactonase activity and glucose-6-phosphate dehydrogenase activity and has a native molecular mass of 178 kDa and a subunit molecular mass of 89 kDa. Glucose 6-phosphate, galactose 6-phosphate, 2-deoxyglucose 6-phosphate, glucosamine 6-phosphate, and glucose 6-sulfate are substrates for murine hexose-6-phosphate dehydrogenase, with either NADP or deamino-NADP as coenzyme. This study confirms that hexose-6-phosphate dehydrogenase is a bifunctional enzyme which can catalyze the first two reactions of the pentose phosphate pathway.

Amino Acid Sequence↗
PubMed1990

Regulation of muscle phosphofructokinase by physiological concentrations of bisphosphorylated hexoses: effect of alkalinization.

To clarify the role of glucose-1,6-P2, fructose-2,6-P2 and fructose-1,6-P2 in the control of the glycolytic flux during muscle contraction, we have determined the activity of muscle phosphofructokinase in the presence of physiological concentrations of these bisphosphorylated hexoses and other allosteric effectors, and at increasing pH values. In the presence of fructose-2,6-P2, both glucose-1,6-P2 and fructose-1,6-P2 can additionally activate the enzyme and partially counteract citrate inhibition. Activation of phosphofructokinase produced by alkalinization increases in the presence of the bisphosphorylated hexoses. It is suggested that the hexose bisphosphates could play a significant role in the initial burst of the glycolytic flux during muscle contraction, when an alkaline pH shift is produced.

Animals↗
PubMed1987

Effect of chronic isoproterenol exposure on insulin binding and insulin-stimulated hexose transport in isolated rat adipocytes.

The effect of chronic exposure of isolated rat adipocytes to the beta-adrenergic agonist isoproterenol has been studied with respect to insulin binding and insulin-stimulated hexose uptake. Isoproterenol exposure led to a progressive decrease in both the number of surface insulin receptors and the stimulation of hexose uptake. The effect on insulin binding was reversible by removal of the beta-agonist within an hour of its addition. Later exposures of adipocytes to isoproterenol resulted in an irreversible cellular defect by leading to a progressive inability of the cells to regain their normal level of insulin-stimulated hexose uptake and insulin binding.

Adipose Tissue↗
PubMed2003

Alterations in hexose, amino acid and peptide transporter expression in intestinal epithelial cells during Nippostrongylus brasiliensis infection in the rat.

Infection with the nematode Nippostrongylus brasiliensis induces various types of cytological alterations in the intestinal villus epithelium. The aim of this study was to analyse the expression of hexose, peptide and amino acid transporters in the small intestinal epithelium after infection. Brown-Norway rats were infected with 2000 N. brasiliensis L3 larvae and villus epithelial cells were isolated at various time points after infection. Expression of hexose transporters Na(+)/glucose cotransporter SGLT1 and glucose transporter GLUT-1, -2 and -5, a peptide transporter (PepT1) and an amino acid transporter (LAT2) was examined by reverse transcription-PCR, Western blotting or immunohistochemistry. Semi-quantitative reverse transcription-PCR studies of separated jejunal epithelial cells showed that expression levels of GLUT5, PepT1 and LAT2 were significantly decreased 7 and 14 days after infection, while these changes were not observed in the ileal epithelium. Although the apical surface glucose transporter SGLT1 showed no significant alteration in mRNA expression, Western blotting analyses of jejunal epithelial cell lysate showed a marked decrease. Contrary to SGLT1, GLUT5, PepT1 and LAT2, expression of GLUT1, which is essential in maintaining high rates of glucose influx, was significantly up-regulated in the jejunal epithelium 7 and 14 days after infection in reverse transcription-PCR as in Western blotting analyses. Immunohistochemical studies showed that GLUT1 immunoreactivity was localised to the basolateral membrane of intestinal epithelial cells 7 days after infection. These results show that N. brasiliensis infection results in an increase in GLUT1 and a decrease in various hexose, amino acid and peptide transporter expression in jejunal epithelial cells. Up-regulation of GLUT1 might be a compensatory response in injured epithelial cells.

Actins↗
PubMed1990

Uridine diphospho sugars and related hexose phosphates in the liver of hexosamine-treated rats: identification using 31P-[1H] two-dimensional NMR with HOHAHA relay.

The effects of administration of galactosamine (GalN) and glucosamine (GlcN) on the levels of UDP-sugars and hexose monophosphates in rat livers were studied by a variety of 31P NMR methods. The flux of metabolites in the liver was monitored by in vivo NMR and showed elevated levels of UDP-sugars, and even greater increases in resonances at 4.6 ppm for GlcN treatment and at 2.0 ppm for GalN treatment. The individual compounds corresponding to these changes were identified in PCA liver extracts by 31P-[1H] two-dimensional relay spectroscopy with a HOHAHA-type 1H spin-lock. This method of transferring proton magnetization allows for nearly all of the proton chemical shifts to be observed for the hexose moiety of a UDP-sugar present in a complex mixture. The UDP-sugars in the extracts from treated rats were predominantly UDP-hexosamines. Relay spectra were also used to determine that GalN-1-P was the major component (16.0 mumol/g of liver) of the GalN-treated liver, while both alpha and beta anomers of GlcNAc-6-P were readily identified as the major hexose monophosphates in the GlcN experiment. Spectra from the 1H dimension of relay experiments conducted on extracts were nearly superimposable on relay spectra obtained under the same conditions for mixtures of standard compounds of known structure. UDP-GlcN and UDP-GalN were not commercially available, but their presence was established in the extracts after GalN treatment by obtaining relay spectra for a mixture of the compounds produced in situ enzymatically, without purification.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2000

Hexose transporters of tomato: molecular cloning, expression analysis and functional characterization.

A full-length (LeHT2) and two partial (LeHT1 and LeHT3) cDNA clones, encoding hexose transporters, were isolated from tomato (Lycopersicon esculentum) fruit and flower cDNA libraries. Southern blot analysis confirmed the presence of a gene family of hexose transporters in tomato consisting of at least three members. The full-length cDNA (LeHT2) encodes a protein of 523 amino acids, with a calculated molecular mass of 57.6 kDa. The predicted protein has 12 putative membrane-spanning domains and belongs to the Major Facilitator Superfamily of membrane carriers. The three clones encode polypeptides that are homologous to other plant monosaccharide transporters and contain conserved amino acid motifs characteristic of this superfamily. Expression of the three genes in different organs of tomato was investigated by quantitative PCR. LeHT1 and LeHT3 are expressed predominantly in sink tissues, with both genes showing highest expression in young fruit and root tips. LeHT2 is expressed at relatively high levels in source leaves and certain sink tissues such as flowers. LeHT2 was functionally expressed in a hexose transport-deficient mutant (RE700A) of Saccharomyces cerevisiae. LeHT2-dependent transport of glucose in RE700A exhibited properties consistent with the operation of an energy-coupled transporter and probably a H+/hexose symporter. The Km of the symporter for glucose is 45 microM.

Amino Acid Sequence↗
PubMed1993

Mammalian facilitative hexose transporters mediate the transport of dehydroascorbic acid.

Although vitamin C is critical to human physiology, it is not clear how it is taken up into cells. The kinetics of cell and tissue accumulation of ascorbic acid in vitro indicate that the process is mediated by specific transporters at the cell membrane. Some experimental observations have linked the transport of ascorbic acid with hexose transport systems in mammalian cells, although no clear information is available regarding the specific role(s) of these transporters, if any, in this process. Here we use the Xenopus laevis oocyte expression system to show that the mammalian facilitative hexose transporters are efficient transporters of the oxidized form of vitamin C (dehydroascorbic acid). Two transport pathways, one with low affinity and one with high affinity for dehydroascorbic acid, were found in oocytes expressing the mammalian transporters, and these oocytes accumulated vitamin C against a concentration gradient when supplied with dehydroascorbic acid. We obtained similar results in experiments using normal human neutrophils. These observations indicate that mammalian facilitative hexose transporters are a physiologically significant pathway for the uptake and accumulation of vitamin C by cells, and suggest a mechanism for the accumulation of ascorbic acid against a concentration gradient.

Animals↗