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PubMed1979

D-Gluconate transport in Arthrobacter pyridinolis. Metabolic trapping of a protonated solute.

D-Gluconate uptake was studied in whole cells of Arthrobacter pyridinolis; the uptake activity was inducible, mutable and showed saturation kinetics (Km = 5 micrometer). Uptake of D-gluconate was not mediated by a phosphoenol-pyruvate : hexose phosphotransferase system, nor was it directly energized by ATP. A transmembrane pH gradient, delta pH, of --63 mV was generated by A. pyridinolis cells at pH 6.5, while at pH 7.5, delta pH = 0. Addition of 8 micrometer D-gluconate significantly reduced the delta pH. The transmembrane electrical potential, delta psi, which was --87 mV over a range of pH from 5.5 to 7.5, was unaffected by the presence of substrate. D-Gluconate accumulated at the same rate and as the protonated solute, at both pH 6.5 and 7.5. Experiments in which a diffusion potential was generated in cyanide-treated cells, indicated that the delta psi did not energize transport. Rather, the rate of D-gluconate uptake metabolism: (a) treatment of cells with valinomycin or nigericin, under conditions in which there was a loss of intracellular potassium, inhibited both D-gluconate uptake and the metabolism of pre-accumulated D-gluconate; (b) the effects of cyanide and azide on D-gluconate uptake were much more severe at pH 6.5 than pH 7.5, a pattern which paralleled the effects of these inhibitors on D-gluconate metabolism; (c) extraction and chromatography of intracellular label from D-gluconate uptake revealed that accumulation of unaltered D-gluconate was negligible; (d) a series of mutant strains with lower D-gluconate kinase activities also exhibited low rates of D-gluconate uptake; (e) spontaneous revertants of these mutant strains consistently regained both D-gluconate kinase activity and wild type levels of uptake.

Arsenates↗
PubMed2005

Identification and characterization of Sulfolobus solfataricus D-gluconate dehydratase: a key enzyme in the non-phosphorylated Entner-Doudoroff pathway.

The extremely thermoacidophilic archaeon Sulfolobus solfataricus utilizes D-glucose as a sole carbon and energy source through the non-phosphorylated Entner-Doudoroff pathway. It has been suggested that this micro-organism metabolizes D-gluconate, the oxidized form of D-glucose, to pyruvate and D-glyceraldehyde by using two unique enzymes, D-gluconate dehydratase and 2-keto-3-deoxy-D-gluconate aldolase. In the present study, we report the purification and characterization of D-gluconate dehydratase from S. solfataricus, which catalyses the conversion of D-gluconate into 2-keto-3-deoxy-D-gluconate. D-Gluconate dehydratase was purified 400-fold from extracts of S. solfataricus by ammonium sulphate fractionation and chromatography on DEAE-Sepharose, Q-Sepharose, phenyl-Sepharose and Mono Q. The native protein showed a molecular mass of 350 kDa by gel filtration, whereas SDS/PAGE analysis provided a molecular mass of 44 kDa, indicating that D-gluconate dehydratase is an octameric protein. The enzyme showed maximal activity at temperatures between 80 and 90 degrees C and pH values between 6.5 and 7.5, and a half-life of 40 min at 100 degrees C. Bivalent metal ions such as Co2+, Mg2+, Mn2+ and Ni2+ activated, whereas EDTA inhibited the enzyme. A metal analysis of the purified protein revealed the presence of one Co2+ ion per enzyme monomer. Of the 22 aldonic acids tested, only D-gluconate served as a substrate, with K(m)=0.45 mM and V(max)=0.15 unit/mg of enzyme. From N-terminal sequences of the purified enzyme, it was found that the gene product of SSO3198 in the S. solfataricus genome database corresponded to D-gluconate dehydratase (gnaD). We also found that the D-gluconate dehydratase of S. solfataricus is a phosphoprotein and that its catalytic activity is regulated by a phosphorylation-dephosphorylation mechanism. This is the first report on biochemical and genetic characterization of D-gluconate dehydratase involved in the non-phosphorylated Entner-Doudoroff pathway.

Amino Acid Sequence↗
PubMed1976

The regulation of transport of glucose, gluconate and 2-oxogluconate and of glucose catabolism in Pseudomonas aeruginosa.

1. The induction by glucose and gluconate of the transport systems and catabolic enzymes for glucose, gluconate and 2-oxogluconate was studied with Pseudomonas aeruginosa PAO1 growing in a chemostat under conditions of nitrogen limitation with citrate as the major carbon source. 2. In the presence of a residual concentration of 30mM-citrate an inflowing glucose concentration of 6-8 mM was required to induce the glucose-transport system and associated catabolic enzymes. When the glucose concentration was raised to 20mM the glucose-transport system was repressed, but the transport system for gluconate, and at higher glucose concentrations, that for 2-oxogluconate, were induced. No repression of the glucose-catabolizing enzymes occurred at the higher inflowing glucose concentrations. 3. In the presence of 30mM-citrate no marked threshold concentration was required for the induction of the gluconate-transport system by added gluconate. 4. In the presence of 30mM-citrate and various concentrations of added glucose and gluconate, the activity of the glucose-transport system accorded with the proposal that a major factor concerned in the repression of this system was the concentration of gluconate, produced extracellularly by glucose dehydrogenase. 5. This proposal was supported by chemostat experiments with mutants defective in glucose dehydrogenase. Such mutants showed no repression of the glucose-transport system by high inflowing concentrations, but with a mutant apparently defective only in glucose dehydrogenase, the addition of gluconate caused repression of the glucose-transport system. 6. Studies with the mutants showed that both glucose and gluconate can induce the enzymes of the Entner-Doudoroff system, whereas for the induction of the gluconate-transport system glucose must be converted into gluconate.

Citrates↗
PubMed1995

Carbon-13 NMR studies and purification of gluconate pathway enzymes from Schizosaccharomyces pombe.

Evidence is presented to show that D-glucose in Schizosaccharomyces pombe can be metabolized via a new alternative route (gluconate pathway) in addition to the regular D-glucose 6-phosphate route. This gluconate pathway consists of two steps: oxidation of D-glucose to D-gluconate by NADP(+)-dependent glucose dehydrogenase and phosphorylation of D-gluconate to 6-phosphogluconate by gluconate kinase. The formation of D-gluconate and 6-phosphogluconate from D-glucose was monitored by 13C nuclear magnetic resonance spectroscopy using D-[1-13C]glucose and D-[U-13C]glucose. The operation of the gluconate pathway was further substantiated by the purification of its two member enzymes, glucose dehydrogenase and gluconate kinase, from the cell-free extract of the fission yeast. Glucose dehydrogenase has been purified (580-fold) to homogeneity by the combined procedures of ammonium sulfate fractionation, Sephadex gel filtration, cation-exchange chromatography, matrex gel chromatography, and agarose-NADP+ affinity chromatography. The purified enzyme is monomeric with a relative molecular weight of 6.65 x 10(4) Da. Gluconate kinase has been purified (410-fold) to near homogeneity by a combination of chromatographic procedures using Bio-gels, matrex gel, and agarose gels. The purified enzyme is monomeric with a relative molecular weight of 2.4 x 10(4) Da. The gluconate pathway presented here provides an alternative route for the D-glucose metabolism in Sch. pombe. Meanwhile, this paper documents another metabolic difference between the fission and budding yeasts.

Carbon Isotopes↗
PubMed2002

Monitoring flux through the oxidative pentose phosphate pathway using [1-14C]gluconate.

The aim of this work was to examine the metabolism of exogenous gluconate by a 4-day-old cell suspension culture of Arabidopsis thaliana (L.) Heynh. Release of (14)CO(2) from [1-(14)C]gluconate was dependent on the concentration in the medium and could be resolved into a substrate-saturable component (apparent K(m) of approximately 0.4 mM) and an unsaturable component. At an external concentration of 0.3 mM, the rate of decarboxylation of applied gluconate was 0.2% of the rate of oxygen consumption by the cells. There was no effect of 0.3 mM gluconate on the rate of oxygen consumption, or on the rate of (14)CO(2) release from either [1-(14)C]glucose or [6-(14)C]glucose by the culture. The following observations argue that gluconate taken up by the cells is metabolised by direct phosphorylation to 6-phosphogluconate and subsequent decarboxylation through 6-phosphogluconate dehydrogenase. First, more than 95% of the label released from [1-(14)C]gluconate during metabolism by the cell culture was recovered as (14)CO(2). Secondly, inhibition of the oxidative pentose phosphate pathway (OPPP) by treatment with 6-aminonicotinamide preferentially inhibited release of (14)CO(2) from [1-(14)C]gluconate relative to that from [1-(14)C]glucose. Thirdly, perturbation of glucose metabolism by glucosamine did not affect (14)CO(2) from [1-(14)C]gluconate. Fourth, stimulation of the OPPP by phenazine methosulphate stimulated release of (14)CO(2) from [1-(14)C]gluconate to a far greater extent than that from [1-(14)C]glucose. It is proposed that measurement of (14)CO(2) from [1-(14)C]gluconate provides a simple and sensitive technique for monitoring flux through the OPPP pathway in plants.

6-Aminonicotinamide↗
PubMed1999

Protection of excitotoxic neuronal death by gluconate through blockade of N-methyl-D-aspartate receptors.

Excitotoxic neuronal death is mediated primarily by the N-methyl-D-aspartate receptor. N-methyl-D-aspartate induces two forms of excitotoxicity in CA1 pyramidal neurons of cultured rat hippocampal slices: the rapidly developing form that depends on external Na+ and Cl-, and the delayed form that requires external Ca2+ but not Cl-. Consistent with this notion, replacement of external Cl- with glucuronate, isethionate or methylsulfate attenuated or delayed selectively the rapid excitotoxicity. However, gluconate substituting for Cl- blocked both rapid and delayed forms of excitotoxicity. Gluconate also reduced N-methyl-D-aspartate-induced membrane currents recorded from CA1 neurons in a dose-dependent manner. This dose-dependence was remarkably similar to that observed for protection of N-methyl-D-aspartate-induced neuronal death by gluconate. Although gluconate chelated Ca2+ most strongly among the four Cl- substitutes examined, excitotoxic neuronal death could be protected by 7 mM gluconate without Ca2+ chelating action. The voltage-dependent Mg2+ block of N-methyl-D-aspartate receptors was not affected by gluconate. Gluconate suppressed the N-methyl-D-aspartate component of excitatory synaptic currents evoked in CA1 neurons. We conclude that protection of excitotoxic neuronal death by gluconate at low doses (<20 mM) is due to its antagonistic action on N-methyl-D-aspartate receptors. Gluconate is a widely used substitute for Cl-. Our unexpected findings give a warning that the results of any of the experiments concerning excitotoxicity or glutamate receptors obtained by gluconate substituting for Cl- must be interpreted with caution.

Animals↗
PubMed2002

Stimulation of butyrate production by gluconic acid in batch culture of pig cecal digesta and identification of butyrate-producing bacteria.

Gluconic acid reaches the large intestine to stimulate lactic acid bacteria. However, the fermentation pattern of gluconic acid has yet to be elucidated. Accordingly, we examined the fermentation properties induced by gluconic acid in the pig cecal digesta in vitro. We also tested sorbitol and glucose, substrates for which the fermentation rate and patterns are known. The gluconic acid-utilizing bacteria were further isolated from pig cecal digesta and identified to examine the effect of gluconic acid on hind gut fermentation. Gluconic acid was fermented more slowly than were the other two substrates. Gluconic acid stimulated butyrate production; the butyrate molar percentage reached 26%, which is considered a high butyrate production. The majority of gluconic acid fermenters were identified as lactic acid bacteria, such as Lactobacillus reuteri and L. mucosae, and acid-utilizing bacteria, such as Megasphaera elsdenii and Mitsuokella multiacida. The gluconic acid fermented by lactic acid bacteria, and the lactate and acetate that were produced were used to form butyrate by acid-utilizing bacteria, such as M. elsdenii. Gluconic acid may be useful as a prebiotic to stimulate butyrate production in the large intestine.

Acetates↗
PubMed2006

Bioconversion of grape must into modulated gluconic acid production by Aspergillus niger ORS-4.410.

AIMS: Analysis of regulators for modulated gluconic acid production under surface fermentation (SF) condition using grape must as the cheap carbohydrate source, by mutant Aspergillus niger ORS-4.410. Replacement of conventional fermentation condition by solid-state surface fermentation (SSF) for semi-continuous production of gluconic acid by pseudo-immobilization of A. niger ORS-4.410. METHODS AND RESULTS: Grape must after rectification was utilized for gluconic acid production in batch fermentation in SF and SSF processes using mutant strain of A. niger ORS-4.410. Use of rectified grape must led to the improved levels of gluconic acid production (80-85 g l(-1)) in the fermentation medium containing 0.075% (NH4)2HPO4; 0.1% KH2PO4 and 0.015% MgSO4.7H2O at an initial pH 6.6 (+/-0.1) under surface fermentation. Gluconic acid production was modulated by incorporating the 2% soybean oil, 2% starch and 1% H2O2 in fermentation medium at continuously high aeration rate (2.0 l min(-1)). Interestingly, 95.8% yield of gluconic acid was obtained when A. niger ORS-4.410 was pseudo-immobilized on cellulose fibres (bagasse) under SSF. Four consecutive fermentation cycles were achieved with a conversion rate of 0.752-0.804 g g(-1) of substrate into gluconic acid under SSF. CONCLUSIONS: Use of additives modulated the gluconic acid production under SF condition. Semi-continuous production of gluconic acid was achieved with pseudo-immobilized mycelia of A. niger ORS-4.410 having a promising yield (95.8%) under SSF condition. SIGNIFICANCE AND IMPACT OF THE STUDY: The bioconversion of grape must into modulated gluconic acid production under SSF conditions can further be employed in fermentation industries by replacing the conventional carbohydrate sources and expensive, energy consuming fermentation processes.

Aspergillus niger↗
PubMed1970

Gluconate catabolism in Rhizobium japonicum.

Gluconate catabolism in Rhizobium japonicum ATCC 10324 was investigated by the radiorespirometric method and by assaying for key enzymes of the major energy-yielding pathways. Specifically labeled gluconate gave the following results for growing cells, with values expressed as per cent (14)CO(2) evolution: C-1 = 93%, C-2 = 57%, C-3 = 30%, C-4 = 70%, C-6 = 39%. The preferential release of (14)CO(2) from C-1 and C-4 indicate that gluconate is degraded primarily by the Entner-Doudoroff pathway but the inequalities between C-1 and C-4 and between C-3 and C-6 indicate that another pathway(s) also participates. The presence of gluconokinase and a system for converting 6-phosphogluconate to pyruvate also indicate a role for the Entner-Doudoroff pathway. The extraordinarily high yield of (14)CO(2) from C-1 labeled gluconate suggests that the other participating pathway is a C-1 decarboxylative pathway. The key enzyme of the pentose phosphate pathway, 6-phosphogluconate dehydrogenase, could not be demonstrated. Specifically labeled 2-ketogluconate and 2,5-diketogluconate were oxidized by gluconate grown cells and gave ratios of C-1 to C-6 of 2.73 and 2.61, respectively. These compare with a ratio of 2.39 obtained with specifically labeled gluconate. Gluconate dehydrogenase, the first enzyme in the ketogluconate pathway found in acetic acid bacteria, was found. Oxidation of specifically labeled pyruvate, acetate, succinate, and glutamate by gluconate-grown cells yielded the preferential rates of (14)CO(2) evolution expected from the operation of the tricarboxylic acid cycle. These data are consistent with the operation of the Entner-Doudoroff pathway and tricarboxylic acid cycle as the primary pathways of gluconate oxidation in R. japonicum. An ancillary pathway for the initial breakdown of gluconate would appear to be the ketogluconate pathway which enters the tricarboxylic acid cycle at alpha-ketoglutarate.

Acetates↗
PubMed2000

Protective mechanisms of Mg-gluconate against oxidative endothelial cytotoxicity.

The potential anti-radical properties and cytoprotective effects of Mg-gluconate were studied. When microsomal membranes were peroxidized by a *O2- driven, Fe-catalyzed oxy-radical system (R* = dihydroxyfumarate + Fe2+), Mg-gluconate inhibited lipid peroxidation (TBARS formation) in a concentration-dependent manner with IC50 being 2.3 mM. For the entire range of .25-2 mM, MgSO4 or MgCl2 were < or = 20% effective compared to Mg-gluconate. When cultured bovine aortic endothelial cells were incubated with the R* for 50 min. at 37 degrees C, 56% loss of total glutathione occurred. Pre-treatment (10 min.) of the cells with 0.25-4 mM Mg-gluconate before R* exposure significantly (p<0.05) prevented the GSH loss to varying degrees; the EC50 was 1.1 mM. In separate experiments, with 30 min. of free radical incubation of endothelial monolayers (approximately 65% confluent), cell survival/proliferation determined by the tetrazolium salt MTT assay, decreased to 38% of control at 24 hrs; Mg-gluconate concentration-dependently attenuated the lost cell survival with EC50 of approximately 1.3 mM. For comparison, the effects provided by MgSO4 or MgCl2 were significantly lower and were < or = 1/3 as potent as that produced by Mg-gluconate. In a Fenton-reaction system consisting of Fe(II)+ H2O2, Mg-gluconate but not other Mg-salts, significantly inhibited the formation of OH radicals as determined by the ESR DMPO-OH signal intensity. Mg-gluconate also dose-dependently inhibited the 'Fe-catalyzed' deoxyribose degradation suggesting that Mg-gluconate could displace Fe from 'catalytic sites' of oxidative damage. These data suggest that Mg-gluconate may serve as a more advantageous Mg-salt for clinical use due to its additional anti-radical and cytoprotective activities.

Animals↗
PubMed1997

The effect of calcium gluconate and other calcium supplements as a dietary calcium source on magnesium absorption in rats.

The effects of commercially available calcium supplements (calcium carbonate, calcium gluconate, oyster shell preparation and bovine bone preparation) and gluconic acid on the absorption of calcium and magnesium were evaluated for 30 days in male Wistar rats. There were no differences in the apparent absorption ratio of calcium among rats fed each calcium supplement; however, the rats fed the calcium gluconate diet had a higher apparent absorption ratio of magnesium than the rats fed the other calcium supplements. Dietary gluconic acid also more markedly stimulated magnesium absorption than the calcium carbonate diet, and the bone (femur and tibia) magnesium contents of rats fed the gluconic acid diet were significantly higher than those of the rats fed the calcium carbonate diet. Furthermore, the weight of cecal tissue and the concentrations of acetic acid and butyric acid in cecal digesta of rats fed the calcium gluconate diet or the gluconic acid diet were significantly increased. We speculate that the stimulation of magnesium absorption in rats fed the calcium gluconate diet is a result of the gluconic acid component and the effect of gluconic acid on magnesium absorption probably results from cecal hypertrophy, magnesium solubility in the large intestine and the effects of volatile fatty acids on magnesium absorption.

Absorption↗
PubMed2003

Continuous gluconic acid production by isolated yeast-like mould strains of Aureobasidium pullulans.

By extensive microbial screening, about 50 strains with the ability to secrete gluconic acid were isolated from wild flowers. The strains belong to the yeast-like mould Aureobasidium pullulans (de Bary) Arnaud. In shake flask experiments, gluconic acid concentrations between 23 and 140 g/l were produced within 2 days using a mineral medium. In batch experiments, various important fermentation parameters influencing gluconic acid production by A. pullulans isolate 70 (DSM 7085) were identified. Continuous production of gluconic acid with free-growing cells of the isolated yeast-like microorganisms was studied. About 260 g/l gluconic acid at total glucose conversion could be achieved using continuous stirred tank reactors in defined media with residence times (RT) of about 26 h. The highest space-time-yield of 19.3 g l(-1) x h(-1)) with a gluconic acid concentration of 207.5 g/l was achieved with a RT of 10.8 h. The possibility of gluconic acid production with biomass retention by immobilised cells on porous sinter glass is discussed. The new continuous gluconate fermentation process provides significant advantages over traditional discontinuous operation employing Aspergillus niger. The aim of this work was the development of a continuous fermentation process for the production of gluconic acid. Process control becomes easier, offering constant product quality and quantity.

Ascomycota↗
PubMed2003

5-keto-D-gluconate production is catalyzed by a quinoprotein glycerol dehydrogenase, major polyol dehydrogenase, in gluconobacter species.

Acetic acid bacteria, especially Gluconobacter species, have been known to catalyze the extensive oxidation of sugar alcohols (polyols) such as D-mannitol, glycerol, D-sorbitol, and so on. Gluconobacter species also oxidize sugars and sugar acids and uniquely accumulate two different keto-D-gluconates, 2-keto-D-gluconate and 5-keto-D-gluconate, in the culture medium by the oxidation of D-gluconate. However, there are still many controversies regarding their enzyme systems, especially on D-sorbitol and also D-gluconate oxidations. Recently, pyrroloquinoline quinone-dependent quinoprotein D-arabitol dehydrogenase and D-sorbitol dehydrogenase have been purified from G. suboxydans, both of which have similar and broad substrate specificity towards several different polyols. In this study, both quinoproteins were shown to be identical based on their immuno-cross-reactivity and also on gene disruption and were suggested to be the same as the previously isolated glycerol dehydrogenase (EC 1.1.99.22). Thus, glycerol dehydrogenase is the major polyol dehydrogenase involved in the oxidation of almost all sugar alcohols in Gluconobacter sp. In addition, the so-called quinoprotein glycerol dehydrogenase was also uniquely shown to oxidize D-gluconate, which was completely different from flavoprotein D-gluconate dehydrogenase (EC 1.1.99.3), which is involved in the production of 2-keto-D-gluconate. The gene disruption experiment and the reconstitution system of the purified enzyme in this study clearly showed that the production of 5-keto-D-gluconate in G. suboxydans is solely dependent on the quinoprotein glycerol dehydrogenase.

Alcohol Oxidoreductases↗