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 55 records · Page 3Linked to original sources
PubMed1996

Regulation by metformin of the hexose transport system in vascular endothelial and smooth muscle cells.

1. The effect of the biguanide metformin on hexose transport activity was studied in bovine cultured aortic endothelial (BEC) and smooth muscle cells (BSMC). 2. Metformin elevated the rate of hexose transport determined with 2-deoxyglucose (2DG) in a dose- and time-dependent manner in both cell types. Similar ED50 values (0.8-1.0 mM) were determined for the effect of metformin on 2DG uptake in both BEC and BSMC following 24 h exposure to increasing concentrations of metformin, with maximal stimulation at 2 mM. 3. In BEC, metformin increased the hexose transport rate 2-3 fold at all glucose concentrations tested (3.3-22.2 mM). In BSMC incubated with 22.2 mM glucose, metformin elevated the hexose transport approximately 2 fold. The drug was also effective at lower glucose levels, but did not exceed the maximal transport rate observed in glucose-deprived cells. 4. Similar results were obtained when the effect of metformin on hexose transport activity was assessed with the non-metabolizable hexose analogue, 3-O-methylglucose, suggesting that the drug affects primarily the rate of hexose transport rather than its subsequent phosphorylation. 5. The metformin-induced increase in hexose transport in BSMC treated for 24 h with the drug correlated with increased abundance of GLUT1 protein in the plasma membrane, as determined by Western blot analysis. 6. These data indicate that in addition to its known effects on hexose metabolism in insulin responsive tissues, metformin also affects the hexose transport system in vascular cells. This may contribute to its blood glucose lowering capacity in patients with Type 2, non-insulin-dependent diabetes mellitus.

Animals↗
PubMed1979

Uncouplers of oxidative phosphorylation promote derepression of the hexose transport system in cultures of hamster cells.

Long-term (18-24 hr) preincubation of NIL hamster cell cultures with D-glucose or D-glucosamine (both of which repress the hexose transport system) gave rise to a striking loss of the hexose transport system ("super-repression") when cycloheximide was also present in the culture medium. However, if 0.2 mM 2,4-dinitrophenol (DNP) was also present, the cycloheximide-mediated super-repression was prevented. Moreover, the presence of DNP at this low concentration contributed to an increase in hexose uptake such that it was substantially higher than that permitted by either of the two repressive sugars alone. When the cultures were maintained in medium containing D-fructose in place of glucose, a marked increase in uptake occurred, and this increase (derepression) was not affected by DNP. The derepression due to glucose deprivation and the increases caused by DNP treatment were also observed when 3-O-methylglucose was used to measure hexose transport. Although cultures maintained in the presence of glucosamine exhibited a repressed hexose transport rate, they did not generate significant amounts of lactic acid. DNP, and other uncouplers of oxidative phosphorylation, promoted a derepressed state of hexose transport but did not stimulate the generation of lactate from glucosamine. These data suggest that the metabolic repression phenomena of hexose transport do not depend on glycolysis but rather on the "energized" state of the cell. The energized state of the cell may also be required for the super-repression of hexose transport that is especially apparent when protein synthesis is blocked by cycloheximide.

Animals↗
PubMed1997

The molecular genetics of hexose transport in yeasts.

Transport across the plasma membrane is the first, obligatory step of hexose utilization. In yeast cells the uptake of hexoses is mediated by a large family of related transporter proteins. In baker's yeast Saccharomyces cerevisiae the genes of 20 different hexose transporter-related proteins have been identified. Six of these transmembrane proteins mediate the metabolically relevant uptake of glucose, fructose and mannose for growth, two others catalyze the transport of only small amounts of these sugars, one protein is a galactose transporter but also able to transport glucose, two transporters act as glucose sensors, two others are involved in the pleiotropic drug resistance process, and the functions of the remaining hexose transporter-related proteins are not yet known. The catabolic hexose transporters exhibit different affinities for their substrates, and expression of their corresponding genes is controlled by the glucose sensors according to the availability of carbon sources. In contrast, milk yeast Kluyveromyces lactis contains only a few different hexose transporters. Genes of other monosaccharide transporter-related proteins have been found in fission yeast Schizosaccharomyces pombe and in the xylose-fermenting yeast Pichia stipitis. However, the molecular genetics of hexose transport in many other yeasts remains to be established. The further characterization of this multigene family of hexose transporters should help to elucidate the role of transport in yeast sugar metabolism.

Biological Transport↗
PubMed1974

The effect of fasting on hexose transfer in rat intestine.

1. A technique has been developed whereby accurately defined segments of rat intestine can be isolated in vivo, and this technique was used to study the influence of fasting on hexose transport.2. In the distal ileum the transport of glucose and galactose was stimulated by fasting. The effect was specific as neither amino acid transport nor the permeability of the luminal membrane of the absorbing epithelium was altered by fasting. The increased hexose transport was accompanied by a reduced accumulation of hexose in the gut wall. In the proximal jejunum hexose transport was not stimulated by fasting.3. The results of in vitro experiments show the relative importance of hexose metabolism in providing energy for transport in different regions of the small intestine in both fed and fasted animals. In conditions where hexose metabolism was reduced, e.g. by fluoride, the proximal jejunum behaved more like the distal ileum and a stimulation of hexose transport in response to fasting was demonstrable in vivo.4. Motility studies showed that phenol red introduced into the stomach reached the ileum sooner, achieved a higher concentration and remained there for a longer period of time in the fasted animal.5. The changes in carbohydrate metabolism, hexose transport capacity and gastrointestinal motility are discussed in relation to adaptations of the rat to fasting.

Animals↗
PubMed1968

Control of dimorphism in Mucor by hexoses: inhibition of hyphal morphogenesis.

In anaerobic cultures of Mucor rouxii, morphogenesis was strongly dependent on hexose concentration as well as pCO(2). At low levels of hexose or CO(2), or both, hyphal development occurred; at high levels, the fungus developed as yeast cells. Other dimorphic strains of Mucor responded similarly to hexose and CO(2) but differred in their relative sensitivity to these agents. Glucose was the most effective hexose in eliciting yeast development of M. rouxii; fructose and mannose were next; and galactose was last. The fungus may be grown into shapes covering its entire dimorphic spectrum simply by manipulating the hexose concentration of the medium. Thus, at 0.01% glucose, hyphae were exceedingly long and narrow; at higher sugar concentrations, the hyphae became progressively shorter and wider; finally, at about 8% glucose, almost all cells and their progeny were isodiametric (spherical budding cells). Such yeast development occurred without a manifested requirement for exogenous CO(2). The stimulation of yeast development by hexose is not an artifact due to increased production of metabolic CO(2) (hyphae or yeast cells released metabolic CO(2) at similar rates). Presumably, the effect was caused by some other hexose catabolite which interfered with hyphal morphogenesis (apical growth); deprived of its polarity, the fungus grew into spherical yeastlike shapes. Although 10% glucose inhibited the development of hyphae from germinating spores, it did not prevent the elongation of preformed hyphae. This suggests that hexose inhibits hyphal morphogenesis not by blocking the operation of the enzyme complex responsible for apical growth but by preventing its initiation; such inhibition may be regarded as a repression of hyphal morphogenesis.

Carbon Dioxide↗
PubMed1986

Partial insulin resistance in the mouse BC3H-1 cell line: absent hexose-independent actions of insulin.

We have studied the regulation of glycogen metabolism by insulin in the insulin-sensitive nonfusing muscle cell line BC3H-1. The basal percentage of glycogen synthase I activity was not altered by insulin alone at any concentration, time of exposure, or age of cells tested. The addition of glucose or 2-deoxyglucose to the glucose- and serum-free incubation medium caused a 2-fold increase in glycogen synthase I activity over basal levels, and the effect was enhanced to 3-fold if insulin was added to the medium. Glycogen phosphorylase a activity was not altered by incubation in the presence of insulin, but was lowered by the addition of 2-deoxyglucose. This effect was also enhanced in the presence of insulin. The effect of exogenously added sugar occurred only if a 6-phosphorylatable hexose was used. The effect seen with 2-deoxyglucose was stable to Sephadex G-25 desalting, suggesting that activation of glycogen synthase was the result of a stable (covalent) modification of the enzyme. We were also able to demonstrate the presence of glucose-6-phosphate-activatable glycogen synthase phosphatase activity in the myocytes. The effect of 2-deoxyglucose in the presence or absence of insulin could be completely reversed by including cytochalasin B in the medium, suggesting that both the effect of hexose and the insulin enhancement of its effect were entirely dependent on carrier-mediated hexose uptake. Four insulin-mimetic agents, H2O2 Concanavalin A, Na orthovanadate, and antiinsulin receptor B2 serum, were also tested. Despite different mechanisms of action, each agent qualitatively mimicked insulin in the myocytes. All stimulated hexose transport, glucose incorporation into glycogen, and hexose-dependent activation of glycogen synthase in a manner not additive with insulin, but none increased basal glycogen synthase I activity in the absence of hexose. These results suggest that although insulin is capable of regulating glycogen metabolism both by increasing the uptake of sugar and by altering the activation state of glycogen synthase and phosphorylase, these effects are entirely due to the stimulation of hexose uptake, and hexose-independent actions of insulin are absent in BC3H-1 cells.

3-O-Methylglucose↗
PubMed1985

Glucose as a regulator of insulin-sensitive hexose uptake in 3T3 adipocytes.

In the present study we examined the role of glucose in the regulation of its own transport activity in the cultured 3T3 fat cell. A regulatory control of glucose became apparent after these cells were cultured in the absence of glucose. Glucose deprivation of the cells was accompanied by a specific time and protein synthesis-dependent increase in dGlc (2-deoxyglucose) uptake (up to 5-fold), which was due to an increase in the apparent Vmax of the transport system. Concomitantly, the stimulatory effect of insulin on hexose uptake almost completely disappeared. Addition of glucose to the glucose-deprived cells rapidly reversed the deprivation effects. Cycloheximide experiments revealed that the glucose deprivation-induced increase in hexose uptake required protein synthesis as well as a protein synthesis-independent response to glucose deprivation that retarded the turnover of hexose transport activity. Taken together, these data indicate that glucose deprivation is accompanied by retardation of the rate of degradation, internalization, or inactivation of hexose transporters while the increase in dGlc uptake requires at least the continuation of protein synthesis-dependent de novo synthesis, insertion, or activation of hexose transporters. Hexose competitively taken up with dGlc, including the nonmetabolizable glucose analogue 3-O-methylglucose, could replace glucose in the process of prevention and reversal of the deprivation effects, indicating that competitive transport but not the metabolism of hexose is a prerequisite for the regulatory effect of glucose on the activity of its own transport system. In conclusion, our results indicate that in cultured 3T3 fat cells glucose itself is involved in the regulation of the activity of its own transport system by influencing the rate of degradation, internalization, or inactivation of hexose transporters by a protein synthesis-independent mechanism.

3-O-Methylglucose↗
PubMed1987

The effects of sulfhydryl modifying reagents on nonhormonal and hormonally regulated hexose transport in cultured human skin fibroblasts.

The effects of various sulfhydryl modifying reagents on hexose transport in cultured human skin fibroblasts were studied. H2O2 was observed to have no effect on 2-deoxy-D-glucose transport in serum-starved glucose-fed cells. The elevation of hexose transport rates in cells by glucose deprivation, insulin, or serum stimulation rendered them sensitive to H2O2. Hexose transport in glucose-deprived cells was inhibited 51-55% by 1-2 mM H2O2, while hexose transport in insulin or serum-stimulated glucose-fed cells was inhibited 45% and 46%, respectively. H2O2 inhibition was blocked or reversed by 8 mM dithiothreitol. N-ethyl-maleimide (NEM), a permeant, sulfhydryl reagent, elicited effects on hexose transport similar to those effected by H2O2 (i.e., in glucose-deprived and insulin-stimulated cells, inhibition of hexose transport was 44% and 23%, respectively). Impermeant sulfhydryl reagents such as dithio(bis)nitrobenzoic acid (DTNB) and N-iodoacetyl-N'-(5-sulfo-1-naphthly-ethylenediame (1,5,-I-AEDANS) had no inhibitory effect on hexose transport under any conditions (i.e., glucose-fed, glucose-deprived, and insulin-stimulated cells). DTNB and 1,5-I-AEDANS afforded no protection from the action of H2O2 on hexose transport. The data suggest that the sensitive sites are thiol in nature and are located at an intramembrane or intracellular site and probably not exofacial.

Cells, Cultured↗
PubMed1992

Inhibitors of protein synthesis cause increased hexose transport in cultured human fibroblasts by a mechanism other than transporter translocation.

We have investigated the effect of various inhibitors of protein synthesis on hexose transport in human skin fibroblasts using 2-deoxy-D-glucose (2-DG) and 3-0-methyl-D-glucose (3-OMG) to measure hexose transport. Exposure of glucose-fed, serum-free cultures to cycloheximide (CHX) (50 micrograms/ml) for 6 h resulted in increased 2-DG transport (3.81 +/- .53 vs. 6.62 +/- .88 nmoles/mg protein/2 min; n = 9) and 3-OMG transport (1.36 +/- .66 vs. 3.18 +/- .83 nmoles/mg protein/30 sec; n = 4) in the CHX exposed group. Under these conditions inhibition of protein synthesis was greater than 90%. This CHX induced transport increase was time dependent (approaching maximum within 1 h of exposure to CHX) and related to an increase in the Vmax of hexose transport in the CHX exposed group (18.4 +/- 2.4 vs. 4.8 +/- 1.1 nmoles 2-DG/mg protein/min) with no difference in the transport Km (1.55 +/- .63 vs. 2.92 +/- .59 mM). Further, the CHX induced increase in hexose transport was reversible. Exposure of human fibroblasts to inhibitors of protein synthesis with different mechanisms of action (e.g., puromycin, pactamycin, or CHX) all generated hexose transport increases in a concentration-dependent fashion correlating with their increasing inhibitory effects on protein synthesis. Nucleotidase enriched (i.e., plasma membrane) fractions of control and CHX-exposed cells showed no differences in D-glucose inhibitable cytochalasin B binding activity. Further, quantitative Western analysis of nucleotidase enriched fractions indicated CHX exposure resulted in no significant increase in glucose transporter mass compared with control plasma membrane fractions. Glucose deprived cells, however, which exhibited increased sugar transport comparable to the CHX-exposed group, did show increased glucose transporter mass in the plasma membrane fraction. The data indicate that inhibitors of protein synthesis can cause a significant elevation in hexose transport and that the hexose transporter mass in the isolated plasma membrane fractions did not reflect the whole cell transport change. It is suggested that a mechanism other than glucose transporter translocation to the plasma membrane may be involved in causing this sugar transport increase.

3-O-Methylglucose↗
PubMed1980

Hexose and amino acid transport by chicken embryo fibroblasts infected with temperature-sensitive mutant of Rous sarcoma virus. Comparison of transport properties of whole cells and membrane vesicles.

The effect of transformation on hexose and amino acid transport has been studied using whole cells and membrane vesicles of chicken embryo fibroblasts infected with the temperature-sensitive mutant of the Rous sarcoma virus, TS-68. In whole cells, TS-68-infected chicken embryo fibroblasts cultured at the permissive temperature (37 degrees C) had a 2-fold higher rate of 2-deoxy-D-glucose uptake than the same cells cultured at the non-permissive temperature (41 degrees C). However, both the non-transformed and transformed cells had comparable rates of alpha-aminoisobutyric acid transport. Membrane vesicles, isolated from TS-68-infected chicken embryo fibroblasts cultured at 41 degrees C or 37 degrees C, displayed carrier-mediated, intravesicular uptake of D-glucose and alpha-aminoisobutyric acid. Membrane vesicles from TS-68-infected chicken embryo fibroblasts cultured at 37 degrees C had an approx. 50% greater initial rate of stereospecific hexose uptake than the membrane vesicles from fibroblasts cultured at 41 degrees C. The two types of membrane vesicle had similar uptake rates of alpha-aminoisobutyric acid. The results of hexose and amino acid uptake by the membrane vesicles correlated well with those observed with the whole cells. Km values for stereospecific D-glucose uptake by the membrane vesicles from TS-68-infected chicken embryo fibroblasts cultured at 41 and 37 degrees C were similar, but the V value was greater for the membrane vesicles from TS-68-infected cells cultured at 37 degrees C. Cytochalasin B competitively inhibited stereospecific hexose uptake in both types of membrane vesicle. These findings suggest that the membrane vesicles retained many of the features of hexose and amino acid transport observed in whole cells, and that the increased rate of hexose transport seen in the virally-transformed chicken embryo fibroblasts was due to an increase in the number or availability of hexose carriers.

Amino Acids↗
PubMed1986

Hexose transport after glucose refeeding of glucose-starved human fibroblasts: 1. The effects of tunicamycin and cycloheximide. 2. Insulin binding and action.

Hexose transport in glucose-starved human fibroblasts was readily reversed by glucose refeeding. This hexose transport reversal was not inhibited by tunicamycin (1.5 microgram/ml) but was blocked by cycloheximide (20 micrograms/ml). The ability of insulin (100 mU/ml) to stimulate hexose transport was returned by glucose refeeding and this was not affected by tunicamycin. Cycloheximide which blocked the glucose refeeding effect on hexose transport, decreased the ability of insulin to stimulate hexose transport. Specific 125I-insulin binding was increased by glucose refeeding of glucose-starved cells and this change in binding was inhibited by tunicamycin and cycloheximide. Thus, it appears that under the conditions employed in human fibroblasts, the ability of insulin to stimulate hexose transport is differentially regulated more by factors affecting basal hexose transport than by those affecting changes in insulin binding.

Biological Transport↗
PubMed1992

Regulation of the functional expression of hexose transporter GLUT-1 by glucose in murine fibroblasts: role of lysosomal degradation.

The nature of the membrane compartments involved in the regulation by glucose of hexose transport is not well defined. The effect of inhibitors of lysosomal protein degradation on hexose transport (i.e., uptake of [3H]-2-deoxy-D-glucose) and hexose transporter protein GLUT-1 (i.e., immunoblotting with antipeptide serum) in glucose-fed and -deprived cultured murine fibroblasts (3T3-C2 cells) was studied. The acidotropic amines chloroquine (20 microM) and ammonium chloride (10 mM) cause accumulation (both approximately 4-fold) of GLUT-1 protein and a small increase (both approximately 25%) in hexose transport in glucose-fed fibroblasts (24 h). The endopeptidase inhibitor, leupeptin (100 microM) causes accumulation (approximately 4-fold) of GLUT-1 protein in glucose-fed fibroblasts (24 h) without changing hexose transport (less than or equal to 5%). These agents do not greatly alter the electrophoretic mobility of GLUT-1. Neither chloroquine nor leupeptin augment the glucose deprivation (24 h) induced increases in hexose transport (approximately 4-fold) and GLUT-1 content (approximately 7-fold). In contrast, chloroquine or leupeptin diminish the reversal by glucose refeeding of the glucose deprivation induced accumulation of GLUT-1 protein but fail to alter the return of hexose transport to control levels.(ABSTRACT TRUNCATED AT 250 WORDS)

3T3 Cells↗
PubMed1973

Two distinct types of enhancement of galactose uptake into hamster cells: tumor-virus transformation and hexose starvation.

Enhancement of hexose uptake seems well correlated with transformation of cell cultures by tumor viruses and the absence of contact inhibition. Enhancement of sugar uptake has also been observed as a result of hexose starvation. Both types of enhancement can clearly be demonstrated in cultures of hamster cells when uptake of (14)C-labeled galactose is monitored after 10 or 20 min. The profiles of accumulation products are strikingly different. In cultures of hamster NIL cells transformed with polyoma virus much of the (14)C is accumulated as UDPhexose. Untransformed cells accumulate galactose-l-phosphate as well as UDPhexose. Hexose-starved cells show enhanced uptake of galactose; however, this marked enhancement was only observed in NIL cultures close to contact inhibition. The novel and common feature seen in hexose-starved cells when incubated briefly with (14)C-labeled galactose is the occurrence of a marked accumulation of [(14)C]UDPglucuronic acid at the expense of UDPhexose. The ratio [(14)C]UDPglucuronic acid/UDPhexose in cultures fed glucose or galactose was invariably low (0.15-0.2) regardless of the presence or absence of contact inhibition. 20 hr of hexose starvation invariably changed this ratio by a factor of 10 or more, due to accumulation of UDPglucuronic acid. This result was also observed in cultures transformed with polyoma virus. The presence of 3-O-methylglucose in the growth medium did not alter the typical "sugar starvation pattern" (i.e., the UDPglucuronic acid/UDPhexose ratio averaged 1.7). Enhancement of galactose uptake by hexose starvation was very pronounced in NIL cultures that were close to contact inhibition, but was not a prominent feature in the polyoma-transformed cultures. The transformed cells grown on glucose or galactose growth medium showed the usual enhanced rate of uptake of galactose as compared with nontransformed near-confluent cultures that had been fed hexose. The polyoma-induced enhancement showed none of the features characteristic of hexosestarved cells.

Animals↗
PubMed1979

Effects of diet, energy restriction and diabetes on hexose transport in the rat.

1. Effects of dietary composition, energy restriction, and diabetes on hexose absorption were examined by feeding male rats isoenergetic, semi-synthetic diets of differing carbohydrate and protein content. Diets were carbohydrate, (g/kg): 890 sucrose; carbohydrate-protien, 500 sucrose, 390 casein; or protein, 890 casein. An additional group was fed on commercial rat chow ad lib. 2. Hexose (3-O-methyl-D-glucose) absorption was measured by luminal perfusion of the entire small intestine in situ. Absorption by the total small intestine, i.e. absorption per rat, and absorption per g dry weight of mucosa (specific absorption) were calculated. 3. When semi-synthetic diets were fed at 210 kJ/d to normal animals absorption depended on composition of diets: carbohydrate enhanced or protein suppressed hexose absorption. Dietary carbohydrate as glucose, dextrimaltose or starch gave the same hexose absorption response as sucrose. 4. When diets of normal rats were restricted to 118 kJ/d, specific absorption was independent of dietary composition and was increased for all dietary groups to the level of the group fed on the carbohydrate diet at 210 kJ/d. 5. When diabetic rats were given 210 kJ/d, hexose specific absorption was the same for all diabetic groups independent of dietary composition and was equal to that of controls given carbohydrate, but greater than that of protein-fed controls. 6. Thus, when two of the three stimuli (i.e. carbohydrate diet plus energy restriction or diabetes) were combined, the effect was not additive, and the response of hexose specific absorption to diabetes and energy restriction was the same: absorption was independent of dietary composition and was stimulated relative to controls fed on diets containing protein. 7. The pattern of response of total small intestinal hexose absorption to the stimuli of dietary composition, energy restriction and diabetes was similar to that of specific absorption. 8. Compared with groups given semi-synthetic diets, rats eating commercial rat chow ad lib. (approximately 286 kJ/d) showed increased mucosal mass and decreased specific absorption, but total absorption was similar to that of the carbohydrate and carbohydrate-protein-fed groups. 9. In a separate study in control rats, specific and total intestinal absorption of L-leucine did not respond to dietary composition, i.e. level of protein fed.

Animals↗
PubMed1988

Properties of hexose-transport regulatory mutants isolated from L6 rat myoblasts.

A hexose-transport regulatory mutant (D1/S4) was isolated from L6 rat myoblasts on the basis of its resistance to detachment and cell lysis in the presence of antibody and complement. Growth studies indicated that D1/S4 cells had a slower doubling time (29 h) compared with the parental L6 cells (22 h). Furthermore, after 9 days growth, less than 1% cell fusion was observed with D1/S4 cells, whereas 95% cell fusion was observed with the L6 cells. When the parental L6 cells were starved of glucose or treated with anti-L6 antibody, a significant increase in the Vmax, of 2-deoxy-D-glucose (dGlc) and 3-O-methyl-D-glucose (MeGlc) transport was observed. Although glucose-grown D1/S4 cells possessed normal hexose-transport activity, the above treatments had no effect on dGlc and MeGlc transport in these cells. Electrophoresis and immunoblotting studies revealed that D1/S4 cells possessed decreased amounts of a 112 kDa plasma-membrane protein. It is conceivable that this protein may play a role in triggering the antibody- and glucose-starvation-mediated activation of hexose transport and in myogenic differentiation. Unlike D1/S4, mutant F72, a mutant defective in the high-affinity hexose-transport system, was found to possess normal amounts of the 112 kDa protein. Although glucose starvation has no effect on the hexose-transport activity in this mutant, its hexose transport activity can be increased by antibody treatment. These studies with mutants suggest the involvement of regulatory components in the activation of hexose transport.

3-O-Methylglucose↗
PubMed1989

Hexose transport in human myoblasts.

The present investigation reports on the hexose transport properties of human myoblasts isolated from normal subjects and from patients with Duchenne muscular dystrophy (DMD). Similar to rat myoblast L6, normal human myoblasts possess a high- (HAHT) and a low- (LAHT) affinity hexose transport system. The non-metabolizable hexose analogue, 2-deoxyglucose, is preferentially taken up by HAHT. The transport of this analogue is the rate-limiting step in the uptake process. This human myoblast HAHT is also similar to that of the rat myoblast in its substrate specificity and in response to the energy uncouplers, cytochalasin B and phloretin. The human myoblast LAHT resembles that of rat myoblast in its insensitivity to energy uncouplers, and in its transport affinity and capacity for 3-O-methyl-D-glucose. Although DMD myoblasts resemble their normal counterpart in their ability to differentiate, they differ significantly in their hexose transport properties. In addition to HAHT and LAHT present in normal human myoblast, DMD myoblasts contain a super-high-affinity hexose transport system (SHAHT). SHAHT can be detected only at very low substrate concentrations. It differs from HAHT not only in its much higher transport affinity, but also in its response to the traditional hexose transport inhibitors. For example, SHAHT can be activated by cytochalasin B and phlorizin, whereas it is more sensitive to inhibition by phloretin. Unlike HAHT, energy uncouplers are found to be ineffective in inhibiting SHAHT. It should be mentioned that SHAHT cannot be detected in myoblasts isolated from patients with other types of myopathy. The present study serves to demonstrate that more than one hexose transport system is operating in human skeletal muscle cells, as found in other cell types.

2,4-Dinitrophenol↗
PubMed1997

Hexose oxidase from the red alga Chondrus crispus. Purification, molecular cloning, and expression in Pichia pastoris.

Hexose oxidase from Chondrus crispus catalyzes the oxidation of a variety of mono- and disaccharides including D-glucose, D-galactose, maltose, and lactose. The enzyme has previously been partially purified and was reported to be a highly glycosylated, copper-containing protein with a relative molecular mass of approximately 130,000 (Sullivan, J. D., and Ikawa, M. (1973) Biochim. Biophys. Acta 309, 11-22). We report here the purification to homogeneity of hexose oxidase from C. crispus. The purified enzyme was cleaved with cyanogen bromide and endoproteinase Lys-C and the peptide fragments were subjected to amino acid sequence analysis. Oligonucleotides were designed on the basis of the peptide sequences and a cDNA clone encoding C. crispus hexose oxidase was obtained using polymerase chain reaction on reverse transcribed cDNA. The nucleotide sequence of the hexose oxidase cDNA contained an open reading frame of 546 amino acid residues with a predicted relative molecular mass of 61,898. No significant sequence similarity was found between hexose oxidase and other protein sequences available in data bases. Expression of the hexose oxidase cDNA in Pichia pastoris as an active enzyme confirmed the identity of the DNA sequence. Native hexose oxidase from C. crispus was characterized and compared with purified, recombinant enzyme.

Alcohol Oxidoreductases↗
PubMed2004

Arsenic trioxide uptake by hexose permeases in Saccharomyces cerevisiae.

Arsenic trioxide is a toxic metalloid and carcinogen that is also used as an anticancer drug, and for this reason it is important to identify the routes of arsenite uptake by cells. In this study the ability of hexose transporters to facilitate arsenic trioxide uptake in Saccharomyces cerevisiae was examined. In the absence of glucose, strains with disruption of the arsenite efflux gene ACR3 accumulated high levels of (73)As(OH)(3). The addition of glucose inhibited uptake by approximately 80%. Disruption of FPS1, the aquaglyceroporin gene, reduced glucose-independent uptake by only about 25%, and the residual uptake was nearly completely inhibited by hexoses, including glucose, galactose, mannose, and fructose but not pentoses or disaccharides. A strain lacking FPS1, ACR3, and all genes for hexose permeases except for HXT3, HXT6, HXT7, and GAL2 exhibited hexose-inhibitable (73)As(OH)(3) uptake, whereas a strain lacking all 18 hexose transport-related genes (HXT1 to HXT17 and GAL2), FPS1 and ACR3, exhibited <10% of wild type (73)As(OH)(3) transport. When HXT1, HXT3, HXT4, HXT5, HXT7, or HXT9 was individually expressed in that strain, hexose-inhibitable (73)As(OH)(3) uptake was restored. In addition, the transport of [(14)C]glucose was inhibited by As(OH)(3). These results clearly demonstrate that hexose permeases catalyze the majority of the transport of the trivalent metalloid arsenic trioxide.

Antineoplastic Agents↗