Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “HEXOSES”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 649 records · Page 36Linked to original sources
PubMed1989

Phosphoglucoisomerase-catalyzed interconversion of hexose phosphates; diastereotopic specificity, isotopic discrimination and intramolecular hydrogen transfer.

When D-[1-3H]fructose 6-phosphate generated from D-[2-3H]glucose 6-phosphate is converted, in a monodirectional manner to D-glucose 6-phosphate and then 6-phospho-D-gluconate, about 42% of the radioactivity is transferred from the C1 of the ketohexose ester to the C2 of the aldohexose phosphate, whereas the remaining 58% are produced as 3H2O. The velocity of the reaction catalyzed by phosphoglucoisomerase represents, in the case of the tritiated substrate, only 43% of that recorded with D-[U-14C]fructose 6-phosphate, such an isotopic discrimination being attributable mainly to a difference in maximal velocity rather than affinity. The phenomena of both intramolecular hydrogen transfer and isotopic discrimination were less pronounced than when D-[2-3H]glucose 6-phosphate is converted, in a monodirectional manner, to D-fructose 6-phosphate and then D-fructose 1,6-bisphosphate. In contrast, when either D-[1-3H]glucose 6-phosphate or D-[1-3H]fructose 6-phosphate prepared from D-[1-3H]glucose were tested, no 3H2O was formed, all radioactivity being recovered, respectively, in tritiated D-fructose 1,6-bisphosphate or NADP3H. Nevertheless, phosphoglucoisomerase was also found to discriminate between D-[U-14C]glucose 6-phosphate and D-[1-3H]glucose 6-phosphate or between D-[U-14C]fructose 6-phosphate and D-[1-3H]fructose 6-phosphate prepared from D-[1-3H]glucose. The reaction velocity with the tritiated esters averaged 78-83% of those recorded with the 14C-labelled esters. Such an isotopic discrimination was again attributable mainly to a difference in maximal velocity rather than affinity. These findings indicate that the mode of preparation of D-[1-3H]fructose cannot be ignored in considering the fate of this tritiated hexose, as ruled by the intrinsic properties, and especially the diastereotopic specificity of phosphoglucoisomerase.

Carbon Radioisotopes↗
PubMed1983

Distribution of three hexose derivatives across the pancreatic epithelium: paracellular shunts or cellular passage?

It has been proposed that the pancreatic epithelium is permeable to three presumably passively distributed non-electrolytes, namely sucrose, inulin and mannitol, via paracellular shunts, and that the increased flux of sucrose and inulin seen during augmented digestive enzyme secretion is due to an increase in the permeability of these shunts. The present study considers this hypothesis by comparing the permeability of the epithelium to three different hexose derivatives, mannitol, inositol and 3-O-methyl-glucose, in both the unstimulated state and after the augmentation of protein secretion with a cholinergic drug. The epithelium was found to be more permeable to mannitol than to either inositol or 3-O-methyl-glucose. In the unstimulated state, the concentration of mannitol in ductal fluid at the steady state was approx. 54% of its concentration in the interstitium, as compared to 12% for inositol and 8% for 3-O-methyl-glucose. Cholinergic stimulation substantially increased the concentration of inositol and 3-O-methyl-glucose in secretion, but did not increase that of mannitol. The increase in the concentration of inositol occurred in the absence of an increase in its rate of transepithelial movement. Taken together, the results suggest that: (1) there is a substantial passage of mannitol through the cells of the epithelial layer, and (2) the increased concentration of inositol and 3-O-methyl-glucose in ductal fluid that occurs with stimulation is due to an increase in their efflux from secretory cells.

3-O-Methylglucose↗
PubMed1988

Hexose metabolism in pancreatic islets. Feedback control of D-glucose oxidation by functional events.

A rise in extracellular D-glucose concentration in pancreatic islet cells causes a greater relative increase in the oxidation of pyruvate and acetyl residues than in glycolysis. A possible explanation for such an unusual situation was sought in the present study. The preferential stimulation of mitochondrial oxidative events was found to display a sigmoidal dependency on hexose concentration, and an exponential time course during prolonged exposure of the islets to a high concentration of D-glucose. The preferential stimulation of mitochondrial oxidative events was abolished in islets incubated in the presence of cycloheximide and absence of Ca2+, in which case the oxidation of D-[6-14C]glucose was more severely inhibited than that of D-[3,4-14C]glucose. Likewise, the inhibitor of protein biosynthesis and the absence of Ca2+ affected the oxidation of L-[U-14C]leucine preferentially, relative to that of L-[1-14C]leucine, in islets exposed to a high, but not a low, concentration of the amino acid. These results demonstrate that in pancreatic islets it is possible to dissociate both glycolysis from mitochondrial oxidative events and the oxidation of acetyl residues from their generation rate. Moreover, the experimental data suggest that nutrient-responsive and ATP-requiring functional processes exert a feedback control on mitochondrial respiration in this fuel-sensor organ.

Animals↗
PubMed1991

Phosphoglucoisomerase-catalyzed interconversion of hexose phosphates: distinction of the 1-monodeutero-isotopomers of D-fructose 6-phosphate by 1H NMR spectroscopy.

The 1H NMR spectrum obtained with the alpha- and beta-anomers of D-[1-2H]fructose 6-phosphate generated from D-glucose 6-phosphate sequentially exposed in D2O to phosphoglucoisomerase, phosphofructokinase and fructose-1,6-diphosphatase differed from that recorded when the deuterated ketohexose phosphate was produced from D-mannose 6-phosphate sequentially exposed in D2O to phosphomannoisomerase, phosphofructokinase and fructose-1,6-diphosphatase. The identification of the 2 isotopomers of D-fructose 6-phosphate by 1H NMR spectroscopy provides a new tool to assess the relative extent of interconversion of hexose phosphates in the reactions catalyzed by phosphoglucoisomerase and phosphomannoisomerase, respectively.

Deuterium↗
PubMed1988

Hexose monophosphate pathway activity in normal and hypoxic rat brain.

Experiments were undertaken to define the role of the alternative route of glucose metabolism in the hexose monophosphate pathway (HMP) during energy balanced, mild brain hypoxia. In similar hypoxic model in spite of the lack of the deficit of high energy compounds, the significant acceleration of glycolysis and inhibition of macromolecular syntheses (lipid, proteins, and nucleic acids) were previously observed. The HMP activity, although directly coupled to intracellular synthetic processes, has not been defined and little is known about the mechanisms of its regulation under brain hypoxia. HMP activity was examined in the rat brain in vivo by estimation of the increment of 6-phosphogluconate concentration after inhibition of its oxidation as achieved by injection of 6-aminonicotinamide. The activity of this alternative route of glucose metabolism was estimated to be 0.4 mmol/h/kg w.w. in the brain cortex and 0.7 mmol/h/kg w.w. in the brain stem. During 2 h of mild hypoxia (7% O2 in N2) the HMP activity dropped to 30% of control level, whereas during first hour of reoxygenation increased to 200% of control. Increased activity of HMP in posthypoxic brain during reoxygenation also was observed in vitro by measuring the rate of [1-14C]- and [6-14C]glucose conversion to 14CO2 in cerebral cortical slices. The possible mechanism of the rapid changes in the activity of HMP induced by hypoxia is discussed. The results suggest that the brain glucose metabolism under mild hypoxia is reoriented toward energy producing pathway (glycolysis) partially at the expense of HMP. The mechanism of this regulation seems not to be directly triggered by energy deficit. Activity of HMP in the brain is in accord with the intracellular synthetic processes and their demands on the metabolites produced by this pathway. Relying upon that, the posthypoxic stimulation of HMP would indicate the metabolic recovery during reoxygenation.

6-Aminonicotinamide↗
PubMed1988

Interrelations between glycolysis and the hexose monophosphate shunt in erythrocytes as studied on the basis of a mathematical model.

A mathematical model is presented which comprises the reactions of glycolysis, the hexose monophosphate shunt (HMS) and the glutathione system in erythrocytes. The model is used to calculate stationary and time-dependent metabolic states of the cell in vitro and in vivo. The model properly accounts for the following metabolic features observed in vitro: (a) stimulation of the oxidative pentose pathway after addition of pyruvate due to a NADP-dependent lactate dehydrogenase as coupling enzyme between glycolysis and the oxidative pentose pathway, (b) relative share of the oxidative pentose pathway in the total consumption of glucose amounting to approximately 10% in the normal case and to approximately 90% under conditions of oxidative stress excreted by methylene blue. From the application of the model to in vivo conditions it is predicted that (c) under normal conditions glycolysis and the HMS are independently regulated by the energetic and oxidative load, respectively, (d) under conditions of enhanced energetic or oxidative load both glycolysis and the HMS are mainly controlled by the hexokinase; in this situation the highest possible values of the energetic and oxidative load which are compatible with cell integrity are strongly coupled and considerably restricted in comparison with the normal case, (e) the stationary states possess bifurcation points at high and low values of the energetic load.

Energy Metabolism↗
PubMed1992

Study of hexose transport, glycerol phosphate shuttle and Krebs cycle in islets of adult rats injected with streptozotocin during the neonatal period.

At 3-4 degrees C, the transport of 3-O-methyl-D-glucose (30 mM) was severely impaired in islets prepared from adult rats injected with streptozotocin during the neonatal period. However, at 37 degrees C, the first and second phase of glucose-stimulated insulin release were decreased to the same relative extent in perifused islets of diabetic, as compared to control, animals. Moreover, the time-related increase in the oxidative response of the islets to 16.7 mM D-glucose was less pronounced in diabetic than control rats. The activity of the mitochondrial FAD-linked glycerophosphate dehydrogenase in islet homogenates of diabetic rats only represented one-fifth of that found in control rats, whereas the activity of the cytosolic NAD-glycerophosphate dehydrogenase was comparable in both types of rats. This coincided with the fact that a rise in D-glucose concentration from 2.8 to 16.7 mM failed to increase significantly L-[2-3H]glycerol conversion to 3HOH in islets from diabetic rats, in contrast to the situation found in control animals. The activity of 2-ketoglutarate dehydrogenase in islet homogenates when expressed per microgram protein was not different in control and diabetic rats. Likewise, the ratio between D-[6-14C]glucose oxidation and D-[3,4-14C]glucose oxidation and the capacity of either a non-metabolized analog of L-leucine or 3-phenylpyruvate to preferentially stimulated D-[6-14C]glucose oxidation relative to D-[5-3H]glucose utilization were both unaffected in islets from diabetic rats. These findings argue against the existence of a primary defect in the Krebs cycle of diabetic rats. It is proposed that, despite an obvious alteration of the hexose transport system in the islet cells of diabetic rats, the preferential impairment of the B-cell secretory response to D-glucose, as distinct from other secretagogues, in this model of non-insulin-dependent diabetes is mainly attributable to the low activity of FAD-linked glycerophosphate dehydrogenase, resulting in a decreased metabolic flow through the glycerol phosphate shuttle and a reduced rate of aerobic glycolysis.

3-O-Methylglucose↗
PubMed1992

Quinone induced stimulation of hexose monophosphate shunt activity in the guinea pig lens: role of zeta-crystallin.

The response of the hexose monophosphate shunt (HMS) in organ-cultured guinea pig lens to 1,2-naphthoquinone and 5-hydroxy-1,4-naphthoquinone (juglone) has been investigated. Both these compounds, which are substrates of guinea pig lens zeta-crystallin (NADPH:quinone oxidoreductase), were found to cause increases in the rate of 14CO2 production from 1-14C-labelled glucose. Exposure of lenses to 15 microM 1,2-naphthoquinone or 20 microM juglone yielded 5.9- and 7-fold stimulation of HMS activity, respectively. Unlike hydrogen peroxide-induced stimulation of HMS activity, these effects were not abolished by preincubation with the glutathione reductase inhibitor, 1,3-bis(2-chloroethyl)-1 nitrosourea (BCNU). While hydrogen peroxide produced substantial decrements in lens glutathione (GSH) levels, incubation with quinones was not associated with a similar reduction in GSH concentration. Protein-bound NADPH content in quinone-exposed guinea pig lenses was decreased, with a concomitant increase in the amounts of free NADP+. This finding supported the involvement of zeta-crystallin bound NADPH in the in vivo enzymic reduction of quinones. Hydrogen peroxide, on the other hand, caused decreases in the level of free NADPH alone, serving to confirm our earlier inference that quinone stimulated increases in the guinea pig lens HMS could be mediated through zeta-crystallin NADPH:quinone oxidoreductase activity.

Animals↗
PubMed1983

Evidence for the homology of hexose 6-phosphate dehydrogenase and glucose 6-phosphate dehydrogenase: comparison of the amino acid compositions.

Amino acid compositions of hexose 6-phosphate dehydrogenase and glucose 6-phosphate dehydrogenase from crucian carp and rat, and that of sea-urchin glucose 6-phosphate dehydrogenase were compared in order to ascertain if they are homologous enzymes. The results demonstrated that the overall amino acid compositions of the two enzymes remarkably resemble each other, and that the composition divergence (D = 0.038) of the crucian carp enzymes is in the range of those for homologous proteins so far reported. These findings strongly support our previous prediction that the two enzymes have diverged from a common ancestral molecule.

Amino Acids↗
PubMed1985

In vitro estimation of the rate of hexose phosphorylation, by sequential pulsing with [3H]- and [14C]2-deoxy-D-glucose.

The rate of phosphorylation of 2-deoxy-D-glucose (2dGlc) was determined by incubating Schistosoma mansoni in vitro in [3H]2-deoxy-D-glucose; 60 sec after exposure to the [3H]dGlc, [14C]dGlc was added to the medium, and metabolic activity was arrested at 2 min by immersion of the tissue in ice-cold silicone oil. Column chromatographic separation of the neutral [3H]- and [14C]dGlc from the [3H]- and [14C]2-deoxy-D-glucose-6-phosphate permitted estimation of the quantity of [3H]dGlc phosphorylated in 2 min, and the proportion of [14C]dGlc phosphorylated in 1 min; thus a phosphorylation rate was determined from a single tissue sample. In male schistosomes derived from mouse infections 4.4 +/- 0.8% of the dGlc was phosphorylated each minute, and 4.2 +/- 0.9% in the females. Lower rates of phosphorylation were measured in schistosomes taken from hamsters where males phosphorylated 2.4 +/- 1.1% of the dGlc each minute, and in females 2.7 +/- 1.0%. These studies suggest the high rate of hexose utilization by schistosomes compares to the conscious rat brain, where 11% of the dGlc is phosphorylated each minute.

Animals↗
PubMed1990

Regulation of D-xylose utilization by hexoses in pentose-fermenting yeasts.

The aldopentose D-xylose is one of the most abundant sugars in plant biomass and its efficient microbial utilization is of fundamental importance in the overall bioconversion of lignocellulosic materials into liquid fuels and chemicals. The discovery of pentose-fermenting yeasts in the early 1980's led to world wide interest because of the perceived potential for improved D-xylose fermentation to enhance the prospect of biomass conversions. However, the utilization of D-xylose by pentose-fermenting yeasts can be adversely affected by the hexoses, mainly D-glucose and D-mannose, which are usually present in high amounts in lignocellulosic hydrolysates. Research in the past several years has uncovered some of the regulatory effects of D-glucose on D-xylose utilization. However, much remains unknown about the mechanisms responsible for these effects. This review summarizes the current state of knowledge on the induction, repression and inactivation of D-xylose utilization in pentose-fermenting yeasts.

Journal Article↗
PubMed1991

Phosphoglucoisomerase-catalyzed interconversion of hexose phosphates. A model for D-[2-3H]glucose metabolism in human erythrocytes.

When D-[2-3H]glucose 6-phosphate mixed with the unlabeled ester is converted to D-[1-3H]fructose 6-phosphate and 3HOH in the phosphoglucoisomerase reaction and then to D-[1-3H]fructose 1,6-bisphosphate in the phosphofructokinase reaction, the specific radioactivity of the latter metabolite and the production of 3HOH relative to the total generation of tritiated end products are both inversely related to the concentration of phosphofructokinase. In human erythrocytes, the modeling of D-[2-3H]glucose metabolism, based on the activity of phosphoglucoisomerase in cell homogenates and on the steady-state content of D-glucose 6-phosphate and D-fructose 6-phosphate in intact cells, indicates that the back-and-forth interconversion of these esters is about five-times higher than the net glycolytic flux. Yet, the production of 3HOH from D-[2-3H]glucose is about 20% lower than the net glycolytic flux, as judged from the production of 3HOH from D-[5-3H]glucose. Thus, an incomplete detriation of D-[2-3H]glucose is not incompatible with an extensive interconversion of hexose 6-phosphates in the reaction catalyzed by phosphoglucoisomerase.

Animals↗
PubMed1994

Growth factor-induced stimulation of hexose transport in 3T3-L1 adipocytes: evidence that insulin-induced translocation of GLUT4 is independent of activation of MAP kinase.

We have examined the effect of growth factors on the rate of hexose transport in 3T3-L1 adipocytes. Epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) were found to stimulate deoxyglucose transport by about 2-fold. The concentrations of EGF and PDGF which elicited half maximal responses were 100 and 350 pM, respectively. The increases in transport rate were acute effects; the stimulations were evident within minutes of exposure to growth factors. By contrast, insulin stimulated deoxyglucose transport approximately 16-fold over similar time periods. We have measured the appearance of both the insulin-responsive glucose transporter (GLUT4) and the erythrocyte-type glucose transporter (GLUT1) at the cell surface in response to insulin, EGF and PDGF. We show that both EGF and PDGF induce a 2-fold increase in GLUT1 at the cell surface, but both these growth factors were without effect on GLUT4 levels at the cell surface. In contrast, insulin induced a 13-fold increase in cell surface GLUT4. We further show that insulin, EGF and PDGF all activate MAP kinase as determined by a shift in electrophoretic mobility of this protein on SDS-PAGE. However, since the large translocation of GLUT4 to the cell surface is specific for insulin, we suggest that activation of MAP kinase is not the sole requisite for this process.

3T3 Cells↗
PubMed1991

Utilization of exogenous glucose-1-phosphate as a source of carbon or phosphate by Escherichia coli K12: respective roles of acid glucose-1-phosphatase, hexose-phosphate permease, phosphoglucomutase and alkaline phosphatase.

The periplasmic acid glucose-1-phosphatase (G-1-Pase) encoded by gene agp is necessary for the growth of Escherichia coli in a minimal medium containing glucose-1-phosphate (G-1-P) as the sole source of carbon. From a mutant in which the agp gene was inactivated, suppressors were isolated which recovered the ability to utilize G-1-P as carbon source. The mutants constitutively expressed hexose phosphate permease activity (encoded by uhpT). The mutation involved mapped in the uhp region and, unlike those of wild-type strains, bacteria of the suppressed strains required phosphoglucomutase (pgm), to grow on G-1-P. Surprisingly, in a minimal medium deprived of inorganic phosphate, uhpT+ bacteria lacking the two enzymes, alkaline-phosphatase (phoA) and glucose-1-phosphatase (agp), could utilize G-1-P as the sole source of phosphate, and also as both the sole phosphate and carbon source provided the integrity of pgm and of uhpT was conserved. Although glucose-6-phosphate, the inducer of UhpT permease, was not present in the medium, the activity of uhpT was greatly stimulated by inorganic phosphate depletion. This phosphate-starvation-induced bypass of G-1-Pase by UhpT + Pgm systems shows that agp is essential for G-1-P assimilation as a carbon source only in a high-phosphate medium, a result in agreement with the lack of agp regulation by inorganic phosphate.

Alkaline Phosphatase↗
PubMed1995

Influence of monosaccharide derivatives on liver cell glycosaminoglycan synthesis: 3-deoxy-D-xylo-hexose (3-deoxy-D-galactose) and methyl (methyl 4-chloro-4-deoxy-beta-D-galactopyranosid) uronate.

An improved, convenient synthesis of 3-deoxy-D-xylo-hexose (3-deoxy-D-galactose) has been developed, and the chemical synthesis of a novel monosaccharide derivative, methyl (methyl 4-chloro-4-deoxy-beta-D-galactopyranosid)uronate (compound 10), is described. Using primary hepatocytes in culture, each was used to explore its effect on glycosaminoglycan (GAG) synthesis. In the absence of analogues hepatocytes synthesize primarily (92-95%) heparan sulphate. At 1 mM, 3-deoxy-D-galactose had little observable effect on either liver cell GAG or protein synthesis. At 10 mM and 20 mM, 3-deoxy-D-galactose reduced [3H]glucosamine and 35SO4 incorporation into hepatocyte cellular GAGs to, respectively, 75% and 60% of the control cells. This inhibition of GAG synthesis occurred without any effect on hepatocyte protein synthesis, indicating that 3-deoxy-D-galactose's effect on GAG synthesis is not mediated through an inhibition of proteoglycan core protein synthesis. Furthermore, GAGs in the presence of 20 mM of the analogue were significantly reduced in size, 17 kDa vs. 66 kDa in untreated cells. These results reflect either impaired cellular GAG chain elongation, and/or altered GAG chain degradation. Compound 10 exhibited a concentration-dependent inhibition of both hepatocyte cellular GAG and protein synthesis. At concentrations of 5, 10 and 20 mM, compound 10 inhibited GAG and protein synthesis by 20, 65 and 90%, respectively. Exogenous uridine was able to restore partially the inhibition of protein synthesis, but was unable to reverse the effect of compound 10 on GAG synthesis. These results show that part of the effect of compound 10 on GAG synthesis is not mediated by an inhibition of proteoglycan core protein synthesis. GAGs in the presence of compound 10 are half as large as those in the absence of this compound (33 and 66 kDa, respectively). These results again may reflect either impaired cellular GAG chain elongation and/or altered GAG chain degradation. Potential metabolic routes for each analogue's effect are presented.

Animals↗
PubMed1994

Unraveling a bacterial hexose transport pathway.

Structural information about proteins involved in bacterial hexose transport mediated by the phosphoenolpyruvate:sugar phosphotransferase system is rapidly accumulating. Within the past year, two crystal structures and two solution NMR structures of the histidine-containing phosphocarrier protein have been reported, adding structural details to previous NMR and crystallographic work on this protein and on enzyme IIA. The crystal structure of the regulatory complex between the glucose enzyme IIA and glycerol kinase has been determined, and the association of the histidine-containing phosphocarrier protein and either the glucose enzyme IIA or the mannitol enzyme IIA have been studied by NMR. Proposals concerning the mechanism of phosphoryl transfer and the protein-protein interactions involved may now be tested more rigorously using these data.

Bacterial Proteins↗
PubMed2005

Probing structure/affinity relationships for the Plasmodium falciparum hexose transporter with glucose derivatives.

A series of 3-O-substituted glucose derivatives was prepared with alkyl, alkenyl, aromatic and ferrocenic substituents; to vary lipophilicity and hydrogen bonding ethylenedioxy and perfluorinated fragments were also introduced. Apparent affinities for the Plasmodium falciparum hexose transporter (PfHT) were determined after heterologous expression in Xenopus oocytes, with highest affinities for compounds with C8-C13 lipophilic chains. As no derivatives show significant affinity for the mammalian glucose transporter (GLUT1), these structure/affinity assays contribute to design of potent PfHT inhibitors and eventual development of antimalarials.

Animals↗
PubMed2004

Hexose-6-phosphate dehydrogenase determines the reaction direction of 11beta-hydroxysteroid dehydrogenase type 1 as an oxoreductase.

The impact of hexose-6-phosphate dehydrogenase (H6PDH) on 11beta-hydroxysteroid dehydrogenase (11beta-HSD) type 1 activity was investigated upon coexpression in HEK-293 cells. Confocal microscopy analysis indicated colocalisation of both enzymes at the lumenal side of the endoplasmic reticulum (ER) membrane. Functional analysis in intact cells revealed fivefold stimulation of 11beta-HSD1 oxoreductase activity and sixfold decrease of dehydrogenase activity upon coexpression with H6PDH, without changing kinetic parameters in cell lysates. Thus, H6PDH directly determines the reaction direction of 11beta-HSD1 in intact cells as an oxoreductase without changing intrinsic catalytic properties of 11beta-HSD1 by regenerating NADPH in the ER-lumen.

11-beta-Hydroxysteroid Dehydrogenases↗