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At least 667 records · Page 37Linked to original sources
PubMed2006

Expression of the Arabidopsis high-affinity hexose transporter STP13 correlates with programmed cell death.

We report the biochemical characterization in Xenopus oocytes of the Arabidopsis thaliana membrane protein, STP13, as a high affinity, hexose-specific H(+)-symporter. Studies with kinase activators suggest that it is negatively regulated by phosphorylation. STP13 promoter GFP reporter lines show GFP expression only in the vascular tissue in emerging petals under non-stressed conditions. Quantitative PCR and the pSTP13-GFP plants show induction of STP13 in programmed cell death (PCD) obtained by treatments with the fungal toxin fumonisin B1 and the pathogen Pseudomonas syringae. A role for STP13 in PCD is supported by microarray data from e.g. plants undergoing senescence and a strong correlation between STP13 transcripts and the PCD phenotype in different accelerated cell death (acd11) mutants.

Animals↗
PubMed2004

A glucose response element from the S. cerevisiae hexose transporter HXT1 gene is sensitive to glucose in human fibroblasts.

Glucose is an essential nutrient, and a regulator of gene expression in eukaryotic cells. Here, a comparative, function-based genomic approach has been used to identify glucose regulatory elements and transduction pathways common to both yeast and mammalian cells. We have isolated a region in the promoter of the Saccharomyces cerevisiae hexose transporter gene HXT1 that conferred glucose sensitivity in yeast, when located upstream of the minimal CYC1 promoter. This element contained binding motifs for Rgt1, a transcriptional modulator involved in the yeast glucose-induction pathway, that were sufficient to elicit glucose responsiveness. The HXT1 regulatory element was then fused to the minimal cytomegalovirus promoter (HXT1-MIN) and inserted into an adenovirus for delivery to human fibroblasts, where it exhibited glucose-dependent transcriptional activation. Glucose action was mimicked by fructose and unrelated to glucose 6-P content, whilst non-metabolizable glucose analogues showed no effect. Activation of AMP kinase by 5-aminoimidazole-4-carboxamide 1-beta-D-ribofuranosanide blocked glucose induction, revealing parallels with the yeast glucose-repressing pathway. In contrast, delivery of Rgt1 to fibroblasts did not modify HXT1-MIN responsiveness. Thus, elements of the S.cerevisiae HXT1 gene conserve glucose regulation in human fibroblasts equivalent to the metabolism-dependent, glucose-repressing pathway in yeast. These data suggest that the instructions carried within gene regulatory elements controlling nutrient regulation of gene expression have been conserved throughout evolution.

Amino Acid Motifs↗
PubMed2005

Cooperativity between 11beta-hydroxysteroid dehydrogenase type 1 and hexose-6-phosphate dehydrogenase is based on a common pyridine nucleotide pool in the lumen of the endoplasmic reticulum.

11Beta-hydroxysteroid dehydrogenase type 1 (11betaHSD1) is a NADP(H)-dependent oxidoreductase of the ER lumen, which may have an important role in the pathogenesis of metabolic syndrome. Here, the functional coupling of 11beta-hydroxysteroid dehydrogenase type 1 and hexose-6-phosphate dehydrogenase (H6PDH) was investigated in rat liver microsomal vesicles. The results demonstrate the existence of a separate intraluminal pyridine nucleotide pool in the hepatic endoplasmic reticulum and a close cooperation between 11betaHSD1 and H6PDH based on their co-localization and the mutual generation of cofactors for each other.

11-beta-Hydroxysteroid Dehydrogenase Type 1↗
PubMed1989

Gas chromatographic-mass spectrometric analysis of hexose monophosphate shunt activity in cultured cells.

A GC/MS method is described for monitoring the relative amount of glucose degraded to lactate via the hexose monophosphate shunt (HMPS) in neoplastic cells. C6 glioma cells were incubated in medium supplemented with [1-13 C]glucose and medium containing [1-13C]glucose with 0.001 mM phenazine methosulfate (PMS). The ratio of the [13C]lactate to [12C]lactate determined from the measurement of the m/z 219/220 and 117/118 ions of the trimethyl silyl derivative, was used to calculate HMPS activity. PMS increased HMPS activity in C6 glioma cells by 3.2 and 4.8 fold at 2 and 12 hours of incubation respectively. GC/MS results were compared with 1H NMR measurements of the [3-13C]lactate/[3-12C]lactate ratio. The GC/MS method was found to require less sample size and yielded better sensitivity than the NMR method.

Animals↗
PubMed1999

Expression of the hexose transporters GLUT1 and GLUT2 during the early development of the human brain.

We used immunohistochemistry with anti-glucose transporter antibodies to document the presence of facilitative hexose transporters in the fetal human brain. GLUT1 is expressed in all regions of the fetal brain from ages 10 to 21 weeks. GLUT1 was present in the endothelial cells of the brain capillaries, the epithelial cells of the choroid plexus and neurons. High expression of GLUT2 was observed in the granular layer of the cerebellum in brains 21 weeks old, but GLUT2 immunoreactivity was absent at earlier stages. GLUT3 and GLUT4 immunoreactivities were absent at all stages studied. GLUT5 immunoreactivity was evident only in the cerebellar region of 21-week old fetal brains. We conclude that GLUT1 plays a fundamental role in early human brain development. The data also suggest that the cerebellum of the developing brain has the capacity to transport fructose, a substrate that has not been previously identified as a source of metabolic energy in the adult human brain.

Brain↗
PubMed1977

Preparation of 3-amino-2,3,6-trideoxy-D-arabino-hexose hydrochloride and its N-trifluoroacetyl derivative.

Methyl 3-acetamido-4,6-O-benzylidene-2,3-dideoxy-alpha-D-arabino-hexopyranoside (5) was converted by treatment with N-bromosuccinimide into the 4-O-benzoyl-6-bromo derivative 6. Reduction with Raney nickel followed by catalytic transesterification of the resultant 4-benzoate 7 afforded methyl 3-acetamido-2,3,6-trideoxy-alpha-D-arabino-hexopyranoside (8), which could readily be converted into the 4-acetate 11. N-Decetylation of 7 and subsequent acid hydrolysis furnished 3-amino-2,3,6-trideoxy-D-arabino-hexose hydrochloride (9), the D enantiomorph of acosamine. The 3-benzamido analog (12) of 8 was prepared from 8 by N-deacetylation and subsequent benzoylation. Hydrolysis of 8 and 12 gave the 3-acetamido (10) and 3-benzamido (13) analogs of 9, which crystallized in the alpha anomeric form. 2,3,6-Trideoxy-3-trifluoro-acetamido-alpha-D-arabino-hexopyranose (15), a key intermediate for the synthesis of glycosidically coupled derivatives of 9, was obtained from 7 by saponification with barium hydroxide followed by N-trifluoracetylation of the resultant glycoside 14 and subsequent selective hydrolysis.

Amino Sugars↗
PubMed2001

Di-tert-butyl diethylphosphoramidite as the phosphitylating reagent in the preparation of 3-deoxy-3-C-methylene-D-ribo-hexose-6-phosphate and 3-deoxy-3-C-methylene-D-erythro-pentose-5-phosphate.

3-Deoxy-3-C-methylene-D-ribo-hexose-6-phosphate and 3-deoxy-3-C-methylene-D-erythro-pentose-5-phosphate were prepared from a common intermediate 3-deoxy-3-C-methylene-1,2-O-isopropylidene-alpha-D-ribo-hexofuranose. The preparation of the phosphorylated unsaturated sugars employed di-tert-butyl diethylphosphoramidite as the phosphitylating reagent. The removal of all the protecting groups was done under acidic conditions in the ultimate step. The unsaturated sugar phosphates were competitive inhibitors but neither substrates nor inactivators of glucose-6-phosphate and ribose-5-phosphate isomerases.

Aldose-Ketose Isomerases↗
PubMed1997

Synthesis of O-methylsulfonyl derivatives of D-glucose as potential alkylating agents for targeted drug delivery to the brain. Evaluation of their interaction with the human erythrocyte GLUT1 hexose transporter.

In order to obtain hydrophilic analogues of 1,4-dimethylsulfonyloxybutane (busulfan) with enhanced selectivity and improved brain penetration, we have synthesized 6-O-methylsulfonyl-D-glucose, 3-O-methylsulfonyl-D-glucose, 3,6-di-O-methylsulfonyl-D-glucose, 4-O-methylsulfonyl-D-glucose, and 4,6-di-O-methylsulfonyl-D-glucose, and we have studied their interactions with the human erythrocyte GLUT1 hexose transport system. Mesylation of OH-4 and OH-6 of glucose resulted in a slightly diminished affinity for the GLUT1 glucose transporter, whereas mesylation of OH-3 led to complete loss of affinity.

Antineoplastic Agents, Alkylating↗
PubMed2002

Starvation-induced degradation of yeast hexose transporter Hxt7p is dependent on endocytosis, autophagy and the terminal sequences of the permease.

The yeast high-affinity glucose transporters Hxt6p and Hxt7p are rapidly degraded during nitrogen starvation in the presence of high concentrations of fermentable carbon sources. Our results suggest that degradation is mainly due to the stimulation of general protein turnover and not caused by a mechanism specifically triggered by glucose. Analysis of Hxt6p/7p stability and cellular distribution in end4, aut2 and apg1 mutants indicates that Hxt7p is internalized by endocytosis, and autophagy is involved in the final delivery of Hxt7p to the vacuole for proteolytic degradation. Internalization and degradation of Hxt7p were blocked after truncation of its N-terminal hydrophilic domain. Nevertheless, this fully functional and stabilized hexose transporter could not maintain fermentation capacity of the yeast cells under starvation conditions, indicating a regulatory constraint on glucose uptake.

Autophagy-Related Protein 5↗
PubMed1998

Catabolite inactivation of the high-affinity hexose transporters Hxt6 and Hxt7 of Saccharomyces cerevisiae occurs in the vacuole after internalization by endocytosis.

After addition of high concentrations of glucose, rates of high-affinity glucose uptake in Saccharomyces cerevisiae decrease rapidly. We found that the high-affinity hexose transporters Hxt6 and Hxt7 are subject to glucose-induced proteolytic degradation (catabolite inactivation). Degradation occurs in the vacuole, as Hxt6/7 were stabilized in proteinase A-deficient mutant cells. Degradation was independent of the proteasome. The half-life of Hxt6 and Hxt7 strongly increased in end4, ren1 and act1 mutant strains, indicating that the proteins are delivered to the vacuole by endocytosis. Moreover, both proteins were also stabilized in mutants defective in ubiquitination. However, the initial signal that triggers catabolite inactivation is not relayed via the glucose sensors Snf3 and Rgt2.

Base Sequence↗
PubMed1994

Hexose-6-kinases in germinating honey locust cotyledons: substrate specificity of D-fructo-6-kinase.

Extracts of the cotyledons of germinated honey locust (Gleditsia triacanthos) seeds, which contain galactomannan as a reserve polysaccharide in the endosperm, were fractionated by chromatography and the fractions examined for the presence of a specific manno-6-kinase which could phosphorylate the D-mannose released by hydrolysis of galactomannan. One particulate hexokinase (the major hexose-6-kinase fraction) and two soluble hexokinase fractions (the minor portion), as well as a soluble fructo-6-kinase fraction, were initially separated. From chromatography, electrophoresis and kinetic studies, no evidence for a specific manno-kinase was obtained. This and the level and kinetic behaviour of the particulate hexokinase implicated it as the enzyme catalysing the phosphorylation of released D-mannose. The fructo-kinase activity was further separated into three fractions. Kinetic studies on one of these with native and synthetic substrates indicated that the structural requirements for the monosaccharide substrate were a beta-D-anomeric 2-OH in the furanose ring, a 4-OH trans to the D-5-CH2OH and a -CH2OH substituent on C2 (trans to the 5-CH2OH) which could be modified. The orientation of the hydroxyl on C-3 had only a limited effect.

Carbohydrate Sequence↗
PubMed2000

Characterization of isoforms of hexose kinases in rice embryo.

Hexose kinases in rice embryos have been characterized. Six isoforms were detected: i.e. three glucokinases (GK1-3), two hexokinases (HK1 and HK2) and one fructokinase (FK1). Out of these, GK3, HK1 and HK2 were inhibited by mannoheptulose and glucosamine, known inhibitors of hexokinase activity. These inhibitors are also known to be modulators of sugar sensing processes. The results suggest that GK3, HK1 and HK2 may play a role in sensing the cellular sugar status in the rice embryo.

Fructokinases↗
PubMed2000

The influence of hexoses addition on the fermentation of d-xylose in Debaryomyces hansenii under continuous cultivation.

The effect of hexoses (glucose and galactose) addition to the feed xylose mineral medium of Debaryomyces hansenii chemostat cultures grown at a constant dilution rate of 0.055 h(-1) was studied. Xylitol was the major product detected amongst all tested conditions. The maximal values for xylitol yield and volumetric productivity (0.56 gg(-1) xylose and 0.21 gl(-1)h(-1), respectively) were obtained for a glucose/xylose feeding ratio of 10%, showing that the addition of small amounts of glucose, but not galactose, enhanced the xylitol production. A xylitol yield increase of 30%, compared with the sole xylose-containing feed medium, was observed. It was found that the oxygen requirement for D. hansenii growth is lower under glucose compared with xylose. Ethanol and glycerol were only produced for glucose/xylose feeding ratio above 30%. The byproducts accumulation was correlated with glucose metabolism, because a direct relationship between the increase of ethanol (and glycerol) concentration and the increase of glucose in the feed medium was found.

Journal Article↗
PubMed1998

[Hexose transporters in humans: their role in insulin sensitivity of peripheral tissues].

UNLABELLED: OBJECTIVES AND JUSTIFICATION: To describe facilitated diffusion glucose transporters (GLUT) in humans, and particularly the regulation of GLUT4 expression since it is predominantly responsible for insulin-mediated glucose transport in muscle and adipose tissue, and plays a crucial role in whole-body glucose homeostasis. MAIN POINTS: Numerous studies have shown abnormal expression of GLUT4 in insulin responsive tissues in diabetes mellitus and other insulin resistant states. The recent development of transgenic mice that overexpress GLUT4 in muscle, adipose tissue, or both has also emphasized the importance of GLUT4 in glucose homeostasis. PERSPECTIVES AND PROJECTS: The studies performed in transgenic mice suggest that strategies to increase GLUT4 transporters in insulin responsive tissues may lead to new therapeutic possibilities to improve insulin sensitivity in insulin resistant states such as non-insulin-dependent diabetes mellitus. CONCLUSIONS: Glucose transport is a crucial process in mammals, which needs specific transmembrane hexose transporters. Each transporter is important in the regulation of glucose homeostasis. Advances in the knowledge of both the action and the regulation of the glucose transport system may provide new insights for the development of therapeutic interventions in diseases such as obesity or diabetes mellitus.

Adipose Tissue↗
PubMed2003

Safety evaluation of a hexose oxidase expressed in Hansenula polymorpha.

A programme of studies was conducted to establish the safety of hexose oxidase (HOX) from Chondrus crispus expressed in the yeast Hansenula polymorpha to be used as a processing aid in the food industry. Rat feeding studies were conducted to assess acute and subchronic oral toxicity. In addition, the potential of the enzyme to cause mutagenicity and chromosomal aberrations was assessed in microbial and tissue culture in vitro studies. Acute and subchronic oral toxicity was not detected at the highest dosage recommended by OECD guidelines. There was no evidence of mutagenic potential or chromosomal aberrations. The no-observed-adverse-effect level (NOAEL) derived from the 13-week study was 5000 units/kg body weight/day. In conclusion it can be considered a safe processing aid for use in the food industry.

Alcohol Oxidoreductases↗
PubMed2000

Chemical and enzymatic synthesis of fructose analogues as probes for import studies by the hexose transporter in parasites.

Various D-fructose analogues modified at C-1 or C-6 positions were synthesized from D-glucose by taking advantage of the Amadori rearrangement or using the aldol condensation between dihydroxyacetone phosphate and appropriate aldehyde catalyzed by fructose 1,6-diphosphate aldolase from rabbit muscle. The affinities of the analogues for the glucose transporter expressed in the mammalian form of Trypanosoma brucei were determined by inhibition of radiolabelled 2-deoxy-D-glucose (2-DOG) transport using zero-trans kinetic analysis. Interestingly, the analogues bearing an aromatic group (i.e. a fluorescence marker) at C-1 or C-6 positions present comparable apparent affinities to D-fructose for the transporter. This result could find applications for hexose transport studies and also provides criteria for the design of glucose import inhibitors.

Animals↗
PubMed1995

Effect of lipid packing on the conformational states of purified GLUT-1 hexose transporter.

The purpose of this study was to determine the effect of increased lipid packing on the conformational states of the GLUT-1 hexose transporter purified in endogenous lipids. The binding of glucose results in a conformational change that can be followed by a decrease in fluorescence intensity. Lipid packing was increased by subjecting the samples to hydrostatic pressure. We have found that in the absence of ligand, the fluorescence intensity decreased approximately 20% in the 600 bar range studied. In the presence of either saturating or half-saturating amounts of D-glucose, a substantial loss in intensity (approximately 80%) was observed. Similar decreases were also seen the presence of a glucose analog, maltose, or a noncompetitive inhibitor, cytochalasin B. Changes in the accessibility of aqueous soluble quenchers (I- and acrylamide) to GLUT-1 Trp and Tyr residues suggested that ligand binding causes interfacial fluorophores to move closer to ionic groups in the lipid head group region of the membrane. This idea was substantiated by (1) increased static quenching of the GLUT-1 fluorophores in the presence of ligand, (2) increased energy transfer efficiency between GLUT-1 fluorophores and a fluorescent membrane probe located close to the head group region, and (3) reduced change in rotational motion with temperature in the presence of ligand. Since the application of pressure results in an increase in bilayer thickness, and ligand binding causes a population of fluorophores to move closer to the membrane surface, then these interfacial interactions can be more stabilized under pressure. Studies monitoring the change in quenching of membrane probes by GLUT-1 tryptophans and energy transfer of GLUT-1 tryptophans to membrane probes support this idea.

Cytochalasin B↗