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PubMed2003

Metabolic engineering for improved fermentation of pentoses by yeasts.

The fermentation of xylose is essential for the bioconversion of lignocellulose to fuels and chemicals, but wild-type strains of Saccharomyces cerevisiae do not metabolize xylose, so researchers have engineered xylose metabolism in this yeast. Glucose transporters mediate xylose uptake, but no transporter specific for xylose has yet been identified. Over-expressing genes for aldose (xylose) reductase, xylitol dehydrogenase and moderate levels of xylulokinase enable xylose assimilation and fermentation, but a balanced supply of NAD(P) and NAD(P)H must be maintained to avoid xylitol production. Reducing production of NADPH by blocking the oxidative pentose phosphate cycle can reduce xylitol formation, but this occurs at the expense of xylose assimilation. Respiration is critical for growth on xylose by both native xylose-fermenting yeasts and recombinant S, cerevisiae. Anaerobic growth by recombinant mutants has been reported. Reducing the respiration capacity of xylose-metabolizing yeasts increases ethanol production. Recently, two routes for arabinose metabolism have been engineered in S. cerevisiae and adapted strains of Pichia stipitis have been shown to ferment hydrolysates with ethanol yields of 0.45 g g(-1) sugar consumed, so commercialization seems feasible for some applications.

Aerobiosis↗
PubMed2001

Transaldolase deficiency: liver cirrhosis associated with a new inborn error in the pentose phosphate pathway.

This article describes the first patient with a deficiency of transaldolase (TALDO1 [E.C.2.2.1.2]). Clinically, the patient presented with liver cirrhosis and hepatosplenomegaly during early infancy. In urine and plasma, elevated concentrations of ribitol, D-arabitol, and erythritol were found. By incubating the patient's lymphoblasts and erythrocytes with ribose-5-phosphate and subsequently analyzing phosphate sugar metabolites, we discovered a deficiency of transaldolase. Sequence analysis of the transaldolase gene from this patient showed a homozygous deletion of 3 bp. This deletion results in absence of serine at position 171 of the transaldolase protein. This amino acid is invariable between species and is located in a conserved region, indicating its importance for enzyme activity. The detection of this new inborn error of pentose metabolism has implications for the diagnostic workup of liver problems of unknown etiology.

Amino Acid Sequence↗
PubMed1964

METABOLISM OF PENTOSES AND PENTITOLS BY AEROBACTER AEROGENES. II. MECHANISM OF ACQUISITION OF KINASE, ISOMERASE, AND DEHYDROGENASE ACTIVITY.

Mortlock, R. P. (Michigan State University, East Lansing), and W. A. Wood. Metabolism of pentoses by Aerobacter aerogenes. II. Mechanism of acquisition of kinase, isomerase, and dehydrogenase activity. J. Bacteriol. 88:845-849. 1964.-Aerobacter aerogenes PRL-R3 possesses the genetic information to synthesize, in the presence of the appropriate inducer, at least three members of the family of ketopentokinases, two members of the family of pentitol dehydrogenases, and two members of the family of aldopentose isomerases. That is, d-xylulokinase, d-ribulokinase, l-ribulokinase, ribitol dehydrogenase, d-arabitol dehydrogenase, d-xylose (--> d-xylulose) isomerase, and l-arabinose (--> l-ribulose) isomerase activities were detectable within 4 hr after addition of inducer. The possibility that mutation and selection are involved in the formation of l-xylulokinase, l-arabitol dehydrogenase, d-arabinose (--> d-ribulose) isomerase and d-lyxose (--> d-xylulose) isomerase could not be eliminated, because 11 hr or more of incubation after the addition of inducer were required before the appearance of these enzyme activities. d-Xylulokinase activity was induced in less than 2 hr when d-xylose or d-arabitol were inducers, but 45 hr were required for the appearance of activity when xylitol was the inducer, and 83 hr were required when d-lyxose was the inducer. Likewise, the time required for induction of ribitol dehydrogenase was 2 hr for ribitol, 12 hr for d-arabinose, and 45 hr for xylitol. The time required for the appearance of enzyme activity correlated with the time required for the beginning of cell growth and substrate utilization.

Alcohols↗
PubMed1965

METABOLISM OF PENTOSES AND PENTITOLS BY AEROBACTER AEROGENES. 3. PHYSICAL AND IMMUNOLOGICAL PROPERTIES OF PENITOL DEHYDROGENASES AND PENTULOKINASES.

Mortlock, R. P. (Michigan State University, East Lansing), D. D. Fossitt, D. H. Petering, and W. A. Wood. Metabolism of pentoses and pentitols by Aerobacter aerogenes. III. Physical and immunological properties of pentitol dehydrogenases and pentulokinases. J. Bacteriol. 89:129-135. 1965.-Four pentulokinases and three pentitol dehydrogenases were purified from Aerobacter aerogenes PRL-R3, and the properties of the enzymes within each family were compared. d-Ribulokinase was purified from cells grown on ribitol, d-arabitol, and xylitol, and from a mutant constitutive for ribitol dehydrogenase; d-xylulokinase, from cells grown on d-xylose and xylitol; l-ribulokinase, from cells grown on l-arabinose; and l-xylulokinase, after growth on l-xylose. Similarly, ribitol dehydrogenase was purified after growth on ribitol, d-arabinose, and xylitol, and from the ribitol dehydrogenase-constitutive mutant. d-Arabitol dehydrogenase was obtained after growth on d-arabitol or d-xylose, and xylitol dehydrogenase was obtained after growth on xylitol. Except for l-xylulokinase, which also had a different S(20) value, the pentulokinases had identical pH optima, K(m) for the ketopentose, and sedimentation constants, and fractionated identically by a number of procedures. These kinases could be distinguished only by their substrate and immunological specificity. Ribitol dehydrogenase and d-arabitol dehydrogenase could be distinguished by several properties, but the properties of xylitol dehydrogenase were always similar to ribitol dehydrogenase. In all cases, individual kinases or dehydrogenases produced by different inducers had identical properties. These data constitute evidence against multiple forms of the same enzyme being produced by different inducers and against the dehydrogenase family containing essentially identical proteins differing only at the active site. For the kinases, three of the four appear to differ only at the active site.

Antibodies↗
PubMedDate not supplied

Stimulation of glucose catabolism through the pentose pathway by the absence of the two pyruvate kinase isoenzymes in Escherichia coli.

Escherichia coli strains devoid of one or both of the two pyruvate kinase isoenzymes (PKA and PKF), were grown on minimal media in batch fermentations. The strain lacking both PKs showed a 28% decrease on its specific growth rate when compared to the wild type. However, protein and CO2 yields did not change. Using radioactive 1-C14 glucose and collecting the CO2 produced by the cultures, it was found that the mutant lacking both pyruvate kinases, metabolized glucose mainly through the pentose pathway (PP). The increased participation of the PP in glucose metabolism in this strain, was also reflected on the levels of the glucose-6-phosphate and 6-phosphogluconate dehydrogenases.

Escherichia coli↗
PubMed1998

Methotrexate: pentose cycle and oxidative stress.

The effect of methotrexate (MTX) and leucovorin (LCV) on pentose cycle enzymes and the activity of enzymes involved in enzyme defence mechanisms against ROS in HeLa cells, were studied. The effect of MTX was also investigated on the cellular levels of glutathione. MTX inhibited the activity of glucose-6-phosphate and 6-phosphogluconate dehydrogenases. The activities of glutathione reductase and gamma-glutamylcysteine synthetase were also inhibited by the drug. No effect was observed on the activities of catalase, superoxide dismutase or transketolase. LCV had no effect on any of the enzymes studied. MTX decreased the cellular levels of glutathione (70 per cent), while the presence of LCV and glutamine did not interfere with the effect of MTX. The net results appear to show that the biological situation resulting from treatment with MTX leads to a reduction of effectiveness of the antioxidant enzyme defence system.

Aminoacyltransferases↗
PubMed1996

In vivo detection by 31P NMR of pentose phosphate pathway block secondary to biochemical modulation.

The chemotherapeutic regimen of N-(phosphonacetyl)-L-aspartate (PALA) followed 17 h later by 6-methylmercaptopurine riboside (MMPR) and 6-aminonicotanamide (6AN) has been shown to be a potent sensitizer of anti-neoplastic therapy. We undertook this study to compare the therapeutic and metabolic effects of this triple drug combination vs one of its components, 6AN, in a murine mammary carcinoma. After treatment with PALA, MMPR and 6AN, a new peak was detected which was assigned to 6-phosphogluconate (6PG), which is a marker of inhibition of the pentose phosphate pathway at the 6-phosphogluconate dehydrogenase step. Treatment with PALA, MMPR and 6AN also induced a decrease in the ratios of nucleoside triphosphate/inorganic phosphate (NTP/Pi) and phosphocreatine/inorganic phosphate (PCr/Pi) similar to previous results with a different tumor model. These effects were most pronounced at 6 and 10 h. In addition, an increase in PME'/phosphocholine (PME' = downfield peak in the phosphomonoester region) was detected, which was expected because of the cytotoxic effect of this regimen. Treatment with 6AN alone also resulted in the detection of 6PG with a maximum intensity at 6 h post-6AN. Treatment with 6AN alone induced a smaller change in PME'/PC and failed to cause a decrease in PCr/Pi or NTP/Pi at 6 and 10 h. The enhanced response to the combination of PALA, MMPR and 6AN vs 6AN alone, both with regard to cytotoxicity and radiosensitization, may be due to energy depletion.

6-Aminonicotinamide↗
PubMed1977

Hormonal sensitivity of human breast tumors in vitro: pentose-shunt activity.

Recent studies indicated that response to endocrine therapy might be predicted in human breast carcinomas using the sensitivity of the pentose-shunt pathway to hormones in organ culture. Thirty breast tumors were examined using this histochemical method, and three independent assessments were made. There was poor agreement between the observers, and we consider that this test is not reproducible in its present form.

Breast Neoplasms↗
PubMed2001

Simple and robust method for estimation of the split between the oxidative pentose phosphate pathway and the Embden-Meyerhof-Parnas pathway in microorganisms.

The flux through the oxidative pentose phosphate (PP) pathway was estimated in Bacillus clausii, Saccharomyces cerevisiae, and Penicillium chrysogenum growing in chemostats with [1-(13)C]glucose as the limiting substrate. The flux calculations were based on a simple algebraic expression that is valid irrespective of isotope rearrangements arising from reversibilities of the reactions in the PP pathway and the upper part of the Embden-Meyerhof-Parnas pathway. The algebraically calculated fluxes were validated by comparing the results with estimates obtained using a numerical method that includes the entire central carbon metabolism. Setting the glucose uptake rate to 100, the algebraic expression yielded estimates of the PP pathway flux in B. clausii, S. cerevisiae, and P. chrysogenum of 20, 42, and 75, respectively. These results are in accordance with the results from the numerical method. The information on the labeling patterns of glucose and the proteinogenic amino acids were obtained using gas chromatography / mass spectrometry, which is a very sensitive technique, and therefore only a small amount of biomass is needed for the analysis. Furthermore, the method developed in this study is fast and readily accessible, as the calculations are based on a simple algebraic expression.

Bacillus↗
PubMed2006

Kinetic modeling to optimize pentose fermentation in Zymomonas mobilis.

Zymomonas mobilis engineered to express four heterologous enzymes required for xylose utilization ferments xylose along with glucose. A network of pentose phosphate (PP) pathway enzymatic reactions interacting with the native glycolytic Entner Doudoroff (ED) pathway has been hypothesized. We have investigated this putative reaction network by developing a kinetic model incorporating all of the enzymatic reactions of the PP and ED pathways, including those catalyzed by the heterologous enzymes. Starting with the experimental literature on in vitro characterization of each enzymatic reaction, we have developed a kinetic model to enable dynamic simulation of intracellular metabolite concentrations along the network of interacting PP and ED metabolic pathways. This kinetic model is useful for performing in silico simulations to predict how varying the different enzyme concentrations will affect intracellular metabolite concentrations and ethanol production rate during continuous fermentation of glucose and xylose mixtures. Among the five enzymes whose concentrations were varied as inputs to the model, ethanol production in the continuous fermentor was optimized when xylose isomerase (XI) was present at the highest level, followed by transaldolase (TAL). Predictions of the model that the interconnecting enzyme phosphoglucose isomerase (PGI) does not need to be overexpressed were recently confirmed through experimental investigations. Through such systematic analysis, we can develop efficient strategies for maximizing the fermentation of both glucose and xylose, while minimizing the expression of heterologous enzymes.

Fermentation↗
PubMed1992

The effect of sammo administration on some fundamental enzymes of pentose phosphate pathway and energy metabolites of alloxanized rats.

Sammo plant which is traditionally used in Egypt for the treatment of diabetes mellitus, was administered at low and high levels (4% and 8% respectively at the expense of starch) to adult male alloxanized albino rats, to study its effect on energy metabolism. Adenosine-5-triphosphate (ATP) in the brain (B), liver (L) and kidneys (K) organs of alloxanized rats was significantly lowered compared with the negative control. On the other hand, adenosine-5-diphosphate (ADP) and adenosine-5-monophosphate (AMP) contents in the same organs were elevated markedly. In this connection myokinase activity in cytoplasmic and mitochondrial fractions of B, L and K organs was stimulated at control. Also, the activities of some fundamental enzymes of the oxidative pentose phosphate pathway i.e. glucose-6-phosphate dehydrogenase (G-6-PD) and 6-phospho-gluconate dehydrogenase (6-PGD) in cytoplasmic and mitochondrial fractions of the same organs were markedly increased. Administration of Sammo at low and high levels reduced the consumption of ATP in B, L and K organs relative to positive control. Whereas, ADP and AMP contents were relatively reduced. Also, myokinase activity in the same organs were relatively inhibited. The activity of G-6-PD and 6-PGD in cytoplasmic and mitochondrial fractions of the same organs were also decreased relative to the positive control.

Adenosine Diphosphate↗
PubMed1998

Endotoxemia, pentose cycle, and the oxidant/antioxidant balance in the hepatic sinusoid.

During the innate immune response, excessive release of reactive oxygen species (ROS) from sequestered phagocytes and activated resident macrophages represents the predominant component of oxidative stress in the liver and other tissues. The consequence of oxidative stress is determined by the status and adaptive changes of antioxidant pathways. In this review, we present evidence that the synchronized response of hepatic sinusoidal endothelial cells, the primary sites of phagocyte attachment, plays an important role in defense against phagocyte-derived ROS. An essential component of the metabolic adaptation of hepatic sinusoidal cells to lipopolysaccharide (LPS)-induced oxidative stress is the stimulated expression of glucose-6-phosphate dehydrogenase (G6PD), the key enzyme of the pentose cycle (hexose monophosphate shunt, HMS). All major ROS-metabolic enzymes, i.e., glutathione peroxidase, glutathione reductase, catalase, superoxide dismutases, NADPH oxidase, and nitric oxide synthase, directly or indirectly depend on NADPH, which is produced in the HMS in these cells. The functional significance of up-regulated HMS within a particular cell type depends on the accompanying adaptive changes in ROS-metabolizing enzymes. In LPS-activated Kupffer cells, the elevated expression of glucose transporter GLUT1 and G6PD mainly serves primed production of superoxide anion, hydrogen peroxide, and nitric oxide. In sinusoidal endothelial cells, the LPS-induced response pattern of glucose- and ROS-metabolizing enzymes results in elevated ROS detoxifying capacity. The described studies also suggest the existence of an intercellular oxidant balance between pro-oxidant Kupffer cells and antioxidant endothelial cells in the hepatic micro-environment. Maintenance of the intercellular oxidant/antioxidant balance between phagocytes and endothelial cells may represent an important mechanism protecting the hepatic parenchyma against exogenous oxidative stress during the inflammatory response.

Animals↗
PubMed2002

Structural characterization of hexoses and pentoses using lead cationization. An electrospray ionization and tandem mass spectrometric study.

The analytical potential of the complexation of isomeric underivatized hexoses (D-glucose, D-galactose, D-mannose, D-talose, D-fructose), methylglycosides (1-O-methyl-alpha-D-glucose and 1-O-methyl-beta-D-glucose) and pentoses (D-ribose, D-xylose, D-arabinose and D-lyxose) by Pb(2+) ions, was investigated by electrospray ionization and tandem mass spectrometry (MS/MS). Pb(2+) ions react mainly with monosaccharides by proton abstraction to generate [Pb(monosaccharide)(m) - H](+) ions (m = 1-3). At low cone voltage, a less abundant series of doubly charged ions of general formula [Pb(monosaccharide)(n)](2+) is also observed. The maximum number n of monosaccharides surrounding a single Pb(2+) ion depends on the metal : monosaccharide ratio. Our study shows that MS/MS experiments have to be performed to differentiate Pb(2+)-coordinated monosaccharides. Upon collision, [Pb(monosaccharide) - H](+) species mainly dissociate according to cross-ring cleavages, leading to the elimination of C(n)H(2n)O(n) neutrals. The various fragmentation processes observed allow the C(1), C(2) and C(4) stereocenters of aldohexoses to be characterized, and also a clear distinction aldoses and fructose. Furthermore, careful analysis of tandem mass spectra also leads to successful aldopentose distinction. Lead cationization combined with MS/MS therefore appears particularly useful to identify underivatized monosaccharides.

Cations, Divalent↗
PubMed2002

Direct stereochemical assignment of hexose and pentose residues in flavonoid O-glycosides by fast atom bombardment and electrospray ionization mass spectrometry.

Mass spectrometric methods have been developed which allow the direct stereochemical assignment of terminal monosaccharide residues in flavonoid O-glycosides without the need for chemical hydrolysis. Standards containing a glucose, galactose, mannose, xylose, arabinose or apiose residue were examined because these monosaccharides are by far the most commonly encountered in flavonoid glycosides. Following acetylation, the major peracetylated sugar related fragments, generated by fast atom bombardment (FAB) or electrospray ionization (ESI), were selected for collisional activation employing a broad range of collision energies. Both FAB and ESI proved to be useful as ionization techniques. Stereoselective fragmentation was achieved and allowed us clearly to differentiate and characterize isomeric monosaccharide residues. The method developed was successfully applied to an unknown flavonoid containing a terminal pentose and hexose residue which was isolated from Farsetia aegyptia.

Flavonoids↗
PubMed2004

Effects of oxidative stress and inhibitors of the pentose phosphate pathway on sexually dimorphic production of IFN-tau by bovine blastocysts.

Bovine interferon-tau (IFN-tau), the anti-luteolytic factor secreted by conceptuses of pecoran ruminants, is a product of autosomal genes, yet in vitro produced (IVP) female expanded blastocysts (EB) secrete about twice as much IFN-tau as males. Two possible explanations have been tested here. One is that embryos of one sex are differentially susceptible to oxidative stress. The second is that female EB produce more IFN-tau because pentose-phosphate pathway (PPP) activity is elevated as a result of delayed X-chromosome inactivation. IVP bovine zygotes were cultured to the 8-cell stage and placed under conditions designed either to promote oxidative stress (+/-H2O2; 20 vs. 5% O2), or to inhibit glucose 6-phosphate dehydrogenase (G6PDH) activity (addition of dehydroepiandrosterone, DHEA or 6-aminonicotinamide, 6-AN to the medium). At day 8, blastocysts were cultured individually for a further 48 hr to assess IFN-tau production, and embryo sex determined retrospectively. Blastocyst numbers were reduced (P < 0.05) and their continued development impaired (P < 0.05) in presence of H2O2 (200 microM) and 20% O2, but neither IFN-tau production nor sexually dimorphic expression of IFN-tau were affected. IFN-tau production was reduced, particularly in females (P < 0.05), and sexual dimorphic differences in production were lost in the presence of both DHEA (100 microM) and 6-AN (1 microM). In the case of 6-AN, these effects were achieved without a significant decline in blastocyst developmental progression, quality, or cell number. The data suggest that the higher production of IFN-tau by female EB is an indirect outcome of the increased activity of the oxidative arm of the PPP pathway.

6-Aminonicotinamide↗
PubMed2005

Involvement of the pentose phosphate pathway and redox regulation in fertilization in the mouse.

Glucose metabolism is necessary for successful fertilization in the mouse. Both spermatozoa and oocytes metabolize glucose through the pentose phosphate pathway (PPP), and NADPH appears required for gamete fusion. The aims of this study were to further characterize the utilization of glucose by the fertilizing spermatozoon and the fertilized oocyte, to demonstrate the importance of the PPP in different steps of fertilization, and to examine whether the beneficial effect of glucose could be mediated by a NADPH-dependent enzyme involved in redox regulation. By using a fluorescent analog of 2-deoxyglucose, glucose uptake was evidenced in both the head and flagellum of motile spermatozoa. After sperm-oocyte fusion, an increase in glucose uptake by the fertilized oocyte was observed but not before the formation of the male and female pronuclei. By using a microphotometric technique, activity of glucose 6-phosphate dehydrogenase (G6PDH), the key enzyme of the PPP, was localized to the sperm head and midpiece. When epididymal spermatozoa were released into a glucose-containing medium, the NADPH/NADP ratio increased with capacitation. Sperm-oocyte fusion and meiosis reinitiation of the fertilized oocyte was inhibited by the PPP inhibitor 6-aminonicotinamide (6-AN); inhibition of sperm-oocyte fusion was relieved by NADPH. Sperm-oocyte fusion and meiosis reinitiation were also inhibited by diphenylamine iodonium, which is a flavoenzyme inhibitor reported to prevent reactive oxygen species (ROS) generation in mouse spermatozoa and embryos. These findings indicate that the PPP is involved in different steps of fertilization. Subsequent regulation of a NADPH-dependent flavoenzyme responsible of ROS production is envisaged.

Animals↗
PubMed2005

Effects of D-glucose concentration, D-fructose, and inhibitors of enzymes of the pentose phosphate pathway on the development and sex ratio of bovine blastocysts.

D-glucose at 5.6 mM reduces the progression of in vitro-produced (IVP) bovine embryos from the morula to the blastocyst stage and skews sex ratio towards males. Possibly, the presence of two transcriptionally active X-chromosomes compromises female embryo development through imbalance in glucose metabolism. Here, we have determined the threshold of embryo sensitivity to glucose, whether substitution of D-fructose for glucose reduces the selective loss of female embryos, and whether inhibition of an X-linked gene product, glucose 6-phosphate dehydrogenase (G6PD), normalizes sex ratio among bovine blastocysts. IVP zygotes were cultured in glucose-free medium to 72 hr post-insemination, at which time 8-cell embryos were selected for treatment and cultured until 144 hr post-insemination. Addition of 4 mM glucose at the 8-cell stage reduced (P < 0.05) the number of blastocyst that formed, whereas 2.5 and 1 mM glucose had no effect. Sex ratio in the presence of 4 and 2.5 mM glucose differed significantly from 0.5, while 1 mM glucose had no effect. D-fructose (5.6 mM) did not compromise development to blastocyst and did not alter the sex ratio of blastocysts that formed. When G6PD inhibitors (dehydroepiandrosterone: DHEA and 6-aminonicotinamide: 6-AN), which effectively inhibit the reduction of the NADPH-sensitive dye, brilliant cresyl blue (BCB) in bovine morulae, were added to the culture medium containing 4 mM glucose, embryo development was moderately reduced, but sex ratio skewing was corrected (with 6-AN) or lowered (with DHEA). In conclusion, glucose above 2.5 mM impairs bovine embryo development and increases sex ratio, most likely as a result of increased pentose-phosphate (PP) pathway activity in female embryos.

Animals↗
PubMed1989

Pathways for the synthesis of sorbitol from 13C-labeled hexoses, pentose, and glycerol in renal papillary tissue.

Suspensions of rabbit renal papillary tissue were incubated with D-[6-13C]glucose, D-[1-13C]fructose, D-[1-13C]ribose, and [2-13C]glycerol. The perchloric acid extracts of the above incubations were investigated with 13C NMR spectroscopy. All 13C-labeled substrates give rise to 13C-labeled D-sorbitol. D-[6-13C]Glucose and D-[1-13C]fructose are converted directly into D-sorbitol via the aldose reductase and sorbitol dehydrogenase pathway, respectively, whereas D-[1-13C]ribose and [2-13C]glycerol give rise to labeling of the D-glyceraldehyde pool which on its turn causes a labeling of D-sorbitol. Label exchanges observed from incubations with glycerol and D-ribose indicate that the pentose shunt plays a role in this synthesis of D-sorbitol.

Animals↗