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PubMed1979

ColE1 hybrid plasmids for Escherichia coli genes of glycolysis and the hexose monophosphate shunt.

The Clarke-Carbon clone bank carrying ColE1-Escherichia coli DNA has been screened by conjugation for complementation of glycolysis and hexose monophosphate shunt mutations. Plasmids were identified for phosphofructokinase (pfkA), triose phosphate isomerase (tpi), phosphoglucose isomerase (pgi), glucose-6-phosphate dehydrogenase (zwf), gluconate-6-phosphate dehydrogenase (gnd), enolase (eno), phosphoglycerate kinase (pgk), and fructose-1,6-P2 aldolase (fda). Enzyme levels for the plasmid-carried gene ranged, for the various plasmids, from 4- to 25-fold the normal level.

Conjugation, Genetic↗
PubMed1981

Exogenous induction of the Escherichia coli hexose phosphate transport system defined by uhp-lac operon fusions.

The uhp-coded hexose phosphate transport system of Escherichia coli is normally induced by the presence of extracellular glucose-6-phosphate (G6P), whereas internally generated G6P does not provide a regulatory signal. Strains carrying uhp-lac operon fusions in which lac operon expression is under the control of the uhpT promoter were isolated. The direction of transcription of the uhp T gene was found to be counterclockwise on the E. coli chromosome map. The effects of added sugar phosphates on induction of beta-galactosidase and G6P uptake activities were compared in two fusion-carrying strains differing only in the presence of functional Uhp+ activity. Induction of uhp expression by G6P was equally effective in the two strains; accumulation of G6P diminished its ability to serve as an inducer. Mannose-6-phosphate was an effective competitive inhibitor of G6P uptake, but did not inhibit induction by G6P of uhp expression. No sugar phosphates were found that inhibited induction by G6P. Inorganic phosphate competitively inhibited induction by G6P whether G6P transport activity was present or not. Thus, the transport activity is not involved in the regulation of its synthesis, and these results strongly support the view that the uhp regulatory system senses only the external environment.

Biological Transport↗
PubMed2000

Hexokinase regulates kinetics of glucose transport and expression of genes encoding hexose transporters in Saccharomyces cerevisiae.

Glucose transport kinetics and mRNA levels of different glucose transporters were determined in Saccharomyces cerevisiae strains expressing different sugar kinases. During exponential growth on glucose, a hxk2 null strain exhibited high-affinity hexose transport associated with an elevated transcription of the genes HXT2 and HXT7, encoding high-affinity transporters, and a diminished expression of the HXT1 and HXT3 genes, encoding low-affinity transporters. Deletion of HXT7 revealed that the high-affinity component is mostly due to HXT7; however, a previously unidentified very-high-affinity component (K(m) = 0.19 mM) appeared to be due to other factors. Expression of genes encoding hexokinases from Schizosaccharomyces pombe or Yarrowia lipolytica in a hxk1 hxk2 glk1 strain prevented derepression of the high-affinity transport system at high concentrations of glucose.

Biological Transport↗
PubMed2002

The first archaeal ATP-dependent glucokinase, from the hyperthermophilic crenarchaeon Aeropyrum pernix, represents a monomeric, extremely thermophilic ROK glucokinase with broad hexose specificity.

An ATP-dependent glucokinase of the hyperthermophilic aerobic crenarchaeon Aeropyrum pernix was purified 230-fold to homogeneity. The enzyme is a monomeric protein with an apparent molecular mass of about 36 kDa. The apparent K(m) values for ATP and glucose (at 90 degrees C and pH 6.2) were 0.42 and 0.044 mM, respectively; the apparent V(max) was about 35 U/mg. The enzyme was specific for ATP as a phosphoryl donor, but showed a broad spectrum for phosphoryl acceptors: in addition to glucose, which showed the highest catalytic efficiency (k(cat)/K(m)), the enzyme also phosphorylates glucosamin, fructose, mannose, and 2-deoxyglucose. Divalent cations were required for maximal activity: Mg(2+), which was most effective, could partially be replaced with Co(2+), Mn(2+), and Ni(2+). The enzyme had a temperature optimum of at least 100 degrees C and showed significant thermostability up to 100 degrees C. The coding function of open reading frame (ORF) APE2091 (Y. Kawarabayasi, Y. Hino, H. Horikawa, S. Yamazaki, Y. Haikawa, K. Jin-no, M. Takahashi, M. Sekine, S. Baba, A. Ankai, H. Kosugi, A. Hosoyama, S. Fukui, Y. Nagai, K. Nishijima, H. Nakazawa, M. Takamiya, S. Masuda, T. Funahashi, T. Tanaka, Y. Kudoh, J. Yamazaki, N. Kushida, A. Oguchi, and H. Kikuchi, DNA Res. 6:83-101, 145-152, 1999), previously annotated as gene glk, coding for ATP-glucokinase of A. pernix, was proved by functional expression in Escherichia coli. The purified recombinant ATP-dependent glucokinase showed a 5-kDa higher molecular mass on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, but almost identical kinetic and thermostability properties in comparison to the native enzyme purified from A. pernix. N-terminal amino acid sequence of the native enzyme revealed that the translation start codon is a GTG 171 bp downstream of the annotated start codon of ORF APE2091. The amino acid sequence deduced from the truncated ORF APE2091 revealed sequence similarity to members of the ROK family, which comprise bacterial sugar kinases and transcriptional repressors. This is the first report of the characterization of an ATP-dependent glucokinase from the domain of Archaea, which differs from its bacterial counterparts by its monomeric structure and its broad specificity for hexoses.

Adenosine Triphosphate↗
PubMed1967

Evidence for the Calvin cycle and hexose monophosphate pathway in Thiobacillus ferrooxidans.

The enzymes of the Calvin reductive pentose phosphate cycle and the hexose monophosphate pathway have been demonstrated in cell-free extracts of Thiobacillus ferrooxidans. This, together with analyses of the products of CO(2) fixation in cell-free systems, suggests that these pathways are operative in whole cells of this microorganism. Nevertheless, the amount of CO(2) fixed in these cell-free systems was limited by the type and amount of compound added as substrate. The inability of cell extracts to regenerate pentose phosphates and to perpetuate the cyclic fixation of CO(2) is partially attributable to low activity of triose phosphate dehydrogenase under the experimental conditions found to be optimal for the enzymes involved in the utilization of ribose-5-phosphate or ribulose-1,5-diphosphate as substrate for CO(2) incorporation. With the exception of ribulose-1,5-diphosphate, all substrates required the addition of adenosine triphosphate (ATP) or adenosine diphosphate (ADP) for CO(2) fixation. Under optimal conditions, with ribose-5-phosphate serving as substrate, each micromole of ATP added resulted in the fixation of 1.5 mumoles of CO(2), whereas each micromole of ADP resulted in 0.5 mumole of CO(2) fixed. These values reflect the activity of adenylate kinase in the extract preparations. The K(m) for ATP in the phosphoribulokinase reaction was 0.91 x 10(-3)m. Kinetic studies conducted with carboxydismutase showed K(m) values of 1.15 x 10(-4)m and 5 x 10(-2)m for ribulose-1,5-diphosphate and bicarbonate, respectively.

Adenine Nucleotides↗
PubMed1995

Three different regulatory mechanisms enable yeast hexose transporter (HXT) genes to be induced by different levels of glucose.

The HXT genes (HXT1 to HXT4) of the yeast Saccharomyces cerevisiae encode hexose transporters. We found that transcription of these genes is induced 10- to 300-fold by glucose. Analysis of glucose induction of HXT gene expression revealed three types of regulation: (i) induction by glucose independent of sugar concentration (HXT3); (ii) induction by low levels of glucose and repression at high glucose concentrations (HXT2 and HXT4); and (iii) induction only at high glucose concentrations (HXT1). The lack of expression of all four HXT genes in the absence of glucose is due to a repression mechanism that requires Rgt1p and Ssn6p. GRR1 seems to encode a positive regulator of HXT expression, since grr1 mutants are defective in glucose induction of all four HXT genes. Mutations in RGT1 suppress the defect in HXT expression caused by grr1 mutations, leading us to propose that glucose induces HXT expression by activating Grr1p, which inhibits the function of the Rgt1p repressor. HXT1 expression is also induced by high glucose levels through another regulatory mechanism: rgt1 mutants still require high levels of glucose for maximal induction of HXT1 expression. The lack of induction of HXT2 and HXT4 expression on high levels of glucose is due to glucose repression: these genes become induced at high glucose concentrations in glucose repression mutants (hxk2, reg1, ssn6, tup1, or mig1). Components of the glucose repression pathway (Hxk2p and Reg1p) are also required for generation of the high-level glucose induction signal for expression of the HXT1 gene. Thus, the glucose repression and glucose induction mechanisms share some of the same components and may share the same primary signal generated from glucose.

Gene Expression↗
PubMed1997

Multiple-drug-resistance phenomenon in the yeast Saccharomyces cerevisiae: involvement of two hexose transporters.

In the yeast Saccharomyces cerevisiae, multidrug resistance to unrelated chemicals can result from overexpression of ATP-binding cassette (ABC) transporters such as Pdr5p, Snq2p, and Yor1p. Expression of these genes is under the control of two homologous zinc finger-containing transcription regulators, Pdr1p and Pdr3p. Here, we describe the isolation, by an in vivo screen, of two new Pdr1p-Pdr3p target genes: HXT11 and HXT9. HXT11 and HXT9, encoding nearly identical proteins, have a high degree of identity to monosaccharide transporters of the major facilitator superfamily (MFS). In this study, we show that the HXT11 product, which allows glucose uptake in a glucose permease mutant (rag1) strain of Kluyveromyces lactis, is also involved in the pleiotropic drug resistance process. Loss of HXT11 and/or HXT9 confers cycloheximide, sulfomethuron methyl, and 4-NQO (4-nitroquinoline-N-oxide) resistance. Conversely, HXT11 overexpression increases sensitivity to these drugs in the wild-type strain, an effect which is more pronounced in a strain having both PDR1 and PDR3 deleted. These data show that the two putative hexose transporters Hxt11p and Hxt9p are transcriptionally regulated by the transcription factors Pdr1p and Pdr3p, which are known to regulate the production of ABC transporters required for drug resistance in yeast. We thus demonstrate the existence of genetic interactions between genes coding for two classes of transporters (ABC and MFS) to control the multidrug resistance process.

DNA-Binding Proteins↗
PubMed1977

Effect of glucocorticoids on the hexose monophosphate pathway in human rheumatoid synovial lining cells in vitro and in vivo.

Human rheumatoid synovial lining cells have up to four times the capacity to oxidize glucose 6-phosphate, the first step of the hexose monophosphate pathway, as do the nonrheumatoid cells. The reducing equivalents produced by this system have many significant metabolic effects. Exposure of these cells by 10(-5) M prednisolone in vitro, or to 6 mg/day in vivo, causes some depression of this activity in the rheumatoid synovial lining cells; less than this dose of steroid, or the administration of nonsteroidal drugs in vivo, has little or no effect. The depression of activity produced by 6 mg/day does not bring this activity down to the value found in nonrheumatoid synoviocytes.

Adult↗
PubMed1988

Epidermal growth factor rapidly activates the hexose monophosphate shunt in kidney cells.

Epidermal growth factor (EGF) is a potent mitogen that rapidly activates plasma membrane Na+-H+ exchangers, thereby causing intracellular alkalinization. The rise in intracellular pH (pHi) may be an important signal for cell growth. However, recent studies have dissociated Na+-H+ exchange activity and/or alkalinization from cellular proliferation. We have studied the role of EGF in the growth of rat renal proximal tubule (PT) cells in primary culture and monitored the early effects of EGF on pHi in these cells using microfluorimetry and the pHi probe, 2',7'-biscarboxyethyl-5(6)-carboxyfluorescein (BCECF). EGF increased DNA synthesis in growing PT cells and produced transient alkalinization (2-3 min) due to activation of Na+-H+ exchange. In contrast, in the absence of extracellular Na+, EGF administration caused pHi to decrease. This acidification was prevented by 2-deoxy-D-glucose and 6-aminonicotinamide, inhibitors of glucose utilization and the hexose monophosphate shunt (HMP), respectively. EGF was also found to stimulate HMP shunt activity in PT cells using an isotopic method for distinguishing between glucose utilization through the HMP shunt vs. glycolysis. Because EGF caused both cytoplasmic acidifying (HMP activation) and alkalinizing (Na+-H+ exchange activation) processes, we propose that the primary role for the activation of Na+-H+ exchange during growth may be to extrude acid from the cell in order to maintain pHi at levels permissive for cell growth.

Animals↗
PubMed1981

Development of brush-border membrane hexose transport system in chick jejunum.

Hexose transport was characterized in jejunal slices and brush-border membrane (BBM) vesicles from chicks of several ages (range: 2 days before hatch to 21 days after hatch). With slices, initial rates of 0.1 mM 3-O-methyl-D-glucose transport were low in --2-, and 0-day chicks, increasing to maximal levels 2-7 days after hatching; rates declined to adult levels over the next 2 wk. Phlorizin did not inhibit uptakes in --2- or 0-day slices. In contrast, about 80% of the uptakes in tissue from 2-day or older chicks was phlorizin inhibitable. The apparent Kt for phlorizin-sensitive transport was the same in slices from 2- (maximal transport rates) and 21-day (minimal posthatch rates) chicks; the apparent Vmax was 2.5 times greater in 2-day slices. With BBM vesicles, initial rates of Na-dependent D-glucose transport and maximal overshoot levels were greater in 2-day vesicles than in 21-day vesicles. As in slice experiments, Kt values were the same in the two preparations, but Vmax values were 1.4 times higher in the 2-day preparation.

Aging↗
PubMed2006

Increased 11beta-hydroxysteroid dehydrogenase type-1 and hexose-6-phosphate dehydrogenase in liver and adipose tissue of rat offspring exposed to alcohol in utero.

Rat offspring prenatally exposed to alcohol display features of metabolic syndrome characterized by a low birth weight, catch-up growth, dyslipidemia, and insulin-resistant diabetes with increased gluconeogenesis, during adult life. Gluconeogenesis is partly regulated by cyclic AMP- and glucocorticoid-dependent mechanisms. Glucocorticoid action at the receptor level depends on its circulating concentrations and is amplified at the prereceptor level by 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1), which regenerates active glucocorticoids from inactive forms. To determine whether 11beta-HSD1 is dysregulated in this rat model, we examined the expression and enzyme activity of 11beta-HSD1 and its regulator enzyme hexose-6-phosphate dehydrogenase (H6PD) in the liver of postnatal day 7 (neonatal) and 3-mo-old (adult) rat offspring prenatally exposed to alcohol. Measurements of 11beta-HSD1 and H6PD were also performed in the omental fat of adult rat offspring. In both neonatal and adult rats, prenatal alcohol exposure resulted in increased tissue corticosterone concentrations, increased expression, and oxoreductase activity of 11beta-HSD1, and a parallel increase of H6PD expression. The data suggest that due to both transcriptional and posttranscriptional dysregulations, rats exposed to alcohol early in life have increased 11beta-HSD1 activity, which may explain insulin-resistant diabetes in these animals later in life.

11-beta-Hydroxysteroid Dehydrogenase Type 1↗
PubMed2004

Active hexose correlated compound enhances the immune function of mice in the hindlimb-unloading model of spaceflight conditions.

Hindlimb unloading is a ground-based model that simulates some of the aspects of spaceflight conditions, including lack of load bearing on hindlimbs and a fluid shift to the head. It has been shown that treatment with active hexose correlated compound (AHCC) restores resistance to infection in mice maintained under hindlimb-unloading conditions. The present study was designed to clarify the mechanisms by which AHCC enhances resistance to infection in this model. We hypothesized that oral administration of AHCC will enhance the function of the immune system, which could lead to the increased resistance to infection observed in this model. AHCC or the excipient was orally administered to mice, and the function of the immune system was assessed in spleen and peritoneal cells isolated from those groups. The results of the present study showed that administration of AHCC for 1 wk before and throughout the second day of the hindlimb-unloading period enhanced the function of the immune system assessed by spleen cell proliferation and cytokine production in spleens and nitric oxide and cytokine production in peritoneal cells. These findings suggest that AHCC can be used as a potent immunoenhancer, especially in cases in which the immune system is suppressed by any condition, including diseases such as human immunodeficiency virus infection and cancer.

Administration, Oral↗
PubMed2004

Sucrose fermentation by Saccharomyces cerevisiae lacking hexose transport.

Sucrose is the major carbon source used by Saccharomyces cerevisiae during production of baker's yeast, fuel ethanol and several distilled beverages. It is generally accepted that sucrose fermentation proceeds through extracellular hydrolysis of the sugar, mediated by the periplasmic invertase, producing glucose and fructose that are transported into the cells and metabolized. In the present work we analyzed the contribution to sucrose fermentation of a poorly characterized pathway of sucrose utilization by S. cerevisiae cells, the active transport of the sugar through the plasma membrane and its intracellular hydrolysis. A yeast strain that lacks the major hexose transporters (hxt1-hxt7 and gal2) is incapable of growing on or fermenting glucose or fructose. Our results show that this hxt-null strain is still able to ferment sucrose due to direct uptake of the sugar into the cells. Deletion of the AGT1 gene, which encodes a high-affinity sucrose-H(+) symporter, rendered cells incapable of sucrose fermentation. Since sucrose is not an inducer of the permease, expression of the AGT1 must be constitutive in order to allow growth of the hxt-null strain on sucrose. The molecular characterization of active sucrose transport and fermentation by S. cerevisiae cells opens new opportunities to optimize yeasts for sugarcane-based industrial processes.

Biological Transport↗
PubMed1984

Pulmonary and hepatic fatty acid synthesis. III. Control of hexose monophosphate shunt pathway by 3,5,3'-L-triiodothyronine.

The hexose monophosphate shunt (HMPS) pathway activities were measured in lung and liver by estimating the relative conversion of [1-14C]-glucose and [6-14C]-glucose into 14CO2 as well as by assaying the glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities. The HMPS activities were depressed in the livers of diabetic and hypophysectomized rats and enhanced by 3,5,3'-L-triiodothyronine (T3) or insulin. The hepatic HMPS activities were stimulated to supranormal levels when normal rats were injected with T3. T3-mediated stimulation of hepatic enzyme activities was dependent on the dose and duration of the hormonal treatment. Half-lives of T3-induced synthesis and degradation of glucose 6-phosphate dehydrogenase were 20 and 96 h, respectively, and of 6-phosphogluconate dehydrogenase were 19 and 90 h, respectively. Although HMPS activity was found in lung, the activities of the HMPS pathway dehydrogenase did not vary with the alteration of hormonal conditions, nor the activities were stimulated by the action of T3 or insulin.

Animals↗
PubMed1987

Glucose flux through the hexose monophosphate shunt and NADP(H) levels during in vitro ageing of human skin fibroblasts.

In cultured human skin fibroblasts the glucose flux through the hexose monophosphate shunt (HMS) amounts to 4% of the glucose flux through the glycolytic pathway. Upon in vitro ageing the rate of glucose utilization through the HMS is decreased more than 50%. This decrease in HMS was not caused by a limiting enzymatic capacity since glucose utilization through the HMS could be raised at least 30-fold in both 'young' and 'aged' fibroblasts upon stimulation with phenazine methosulphate. This effect of in vitro ageing upon glucose metabolism was also not due to differences in proliferation rate between 'young' and 'aged' human fibroblasts, since there was no difference in glucose utilization between proliferating and growth-inhibited (confluently cultured) fibroblasts. The NADPH/NADP ratio was found to be decreased by 12% in 'aged' cells.

Adult↗
PubMed1988

Hexose monophosphate shunt enzymes in lung tumors from normal and glucose-6-phosphate-dehydrogenase-deficient subjects.

Glucose-6-phosphate dehydrogenase (G6PD) and 6-phosphogluconate, dehydrogenase the key enzymes of the hexose monophosphate shunt pathway, were measured in both surrounding and tumoral lung tissues from normal and G6PD-deficient subjects. A significant increase of these enzymatic activities in tumoral tissue was found not only in G6PD-normal patients, but also in G6PD-deficient patients with very low or nonmeasurable G6PD activity in both erythrocytes and normal lung tissue.

Adult↗