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PubMed1964

EXTRACELLULAR POLYSACCHARIDES OF ALGAE: EFFECTS ON LIFE-SUPPORT SYSTEMS.

The amount of extracellular polysaccharide produced by eight species of green and blue-green algae ranges from 174 milligrams per liter to 557 milligrams per liter. Most of the polymers are composed of four monosaccharides: a hexose, a pentose, a methyl pentose, and uronic acid. The production of excessive amounts of these photosynthetic end products will undoubtedly influence the effective recycling time of growth media in life-support systems.

Arabinose↗
PubMed2006

Transcriptional and metabolic responses of Bacillus subtilis to the availability of organic acids: transcription regulation is important but not sufficient to account for metabolic adaptation.

The soil bacterium Bacillus subtilis can use sugars or organic acids as sources of carbon and energy. These nutrients are metabolized by glycolysis, the pentose phosphate pathway, and the Krebs citric acid cycle. While the response of B. subtilis to the availability of sugars is well understood, much less is known about the changes in metabolism if organic acids feeding into the Krebs cycle are provided. If B. subtilis is supplied with succinate and glutamate in addition to glucose, the cells readjust their metabolism as determined by transcriptome and metabolic flux analyses. The portion of glucose-6-phosphate that feeds into the pentose phosphate pathway is significantly increased in the presence of organic acids. Similarly, important changes were detected at the level of pyruvate and acetyl coenzyme A (acetyl-CoA). In the presence of organic acids, oxaloacetate formation is strongly reduced, whereas the formation of lactate is significantly increased. The alsSD operon required for acetoin formation is strongly induced in the presence of organic acids; however, no acetoin formation was observed. The recently discovered phosphorylation of acetolactate decarboxylase may provide an additional level of control of metabolism. In the presence of organic acids, both types of analyses suggest that acetyl-CoA was catabolized to acetate rather than used for feeding the Krebs cycle. Our results suggest that future work has to concentrate on the posttranslational mechanisms of metabolic regulation.

Adaptation, Physiological↗
PubMed1996

Development of an arabinose-fermenting Zymomonas mobilis strain by metabolic pathway engineering.

The substrate fermentation range of the ethanologenic bacterium Zymomonas mobilis was expanded to include the pentose sugar, L-arabinose, which is commonly found in agricultural residues and other lignocellulosic biomass. Five genes, encoding L-arabinose isomerase (araA), L-ribulokinase (araB), L-ribulose-5-phosphate-4-epimerase (araD), transaldolase (talB), and transketolase (tktA), were isolated from Escherichia coli and introduced into Z. mobilis under the control of constitutive promoters that permitted their expression even in the presence of glucose. The engineered strain grew on and produced ethanol from L-arabinose as a sole C source at 98% of the maximum theoretical ethanol yield, based on the amount of consumed sugar. This indicates that arabinose was metabolized almost exclusively to ethanol as the sole fermentation product, with little by-product formation. Although no diauxic growth pattern was evident, the microorganism preferentially utilized glucose before arabinose, apparently reflecting the specificity of the indigenous facilitated diffusion transport system. This microorganism may be useful, along with the previously developed xylose-fermenting Z. mobilis (M. Zhang, C. Eddy, K. Deanda, M. Finkelstein, and S. Picataggio, Science 267:240-243, 1995), in a mixed culture for efficient fermentation of the predominant hexose and pentose sugars in agricultural residues and other lignocellulosic feedstocks to ethanol.

Arabinose↗
PubMed1969

Transketolase mutants of Escherichia coli.

Transketolase mutants have been selected after ethyl methane sulfonate mutagenesis of Escherichia coli. These strains are unable to grow on any pentose and, in addition, require a supplement of aromatic amino acids or shikimic acid for normal growth on any other carbon source. Revertants are normal in both respects and also contain transketolase. Transketolase mutants do not require exogenous pentose for growth. Preliminary genetic mapping of the locus is presented.

Chromosome Mapping↗
PubMed1982

Pseudomonas cepacia mutants blocked in the Entner-Doudoroff pathway.

Pseudomonas cepacia mutants deficient in either 6-phosphogluconate (6PGA) dehydratase (Edd-) or 2-keto-3-deoxy-6-phosphogluconate (KDPG) aldolase (Eda-) failed to utilize glucose or gluconate despite the prominence of of 6-phosphogluconate dehydrogenase (6PGAD) ii this bacterium and the potential for utilizing the pentose shunt suggested by its growth on ribitol and xylose. The Eda- strains grew normally on glucuronic acid, indicating that in P. cepacia its degradation does not depend upon KDPG aldolase as it does in Escherichia coli. Both 6PGA dehydratase and KDPG aldolase were inducible enzymes, with 6PGA rather than gluconate the apparent inducer. Edd- as well as Eda- strains were sensitive to growth inhibition by glucose, gluconate, fructose, and related carbohydrates when these substrates were present in combination with alternate carbon sources such as citrate or phthalate, presumably as a consequence of accumulation and toxicity of 6PGA, KDPG, or both. Edd- mutants were somewhat less sensitive to such inhibition than were Eda- strains. Certain derivatives of the Edd- strains we examined were able to utilize gluconate despite their deficiency of 6PGA dehydratase. Such mutants formed higher levels of 6PGAD than did the wild type. It is likely that the elevated levels of 6PGAD in these strains prevents accumulation of toxic levels of 6PGA that would otherwise result from a block in he Entner-Doudoroff pathway. The results suggest that P. cepacia can mutate to grow slowly on gluconate utilizing only the pentose shunt.

Aldehyde-Lyases↗
PubMed1993

D-arabitol metabolism in Candida albicans: studies of the biosynthetic pathway and the gene that encodes NAD-dependent D-arabitol dehydrogenase.

Candida albicans produces large amounts of the pentitol D-arabitol in culture and in infected mammalian hosts, but the functional and pathogenic significance of D-arabitol in C. albicans is not known. In this study, we sought to elucidate the pathway by which C. albicans synthesizes D-arabitol and to identify and characterize key enzymes in this pathway. C. albicans B311 produced D-[14C-1]arabitol from [14C-2]glucose; this finding implies on structural grounds that D-ribulose-5-PO4 from the pentose pathway is the major metabolic precursor of D-arabitol. NAD- or NADP-dependent pentitol dehydrogenases catalyze the final steps in D-arabitol biosynthesis in other fungi; therefore, lysates of C. albicans B311 were tested for enzymes of this class and were found to contain a previously unknown NAD-dependent D-arabitol dehydrogenase (ArDH). The ArDH structural gene was cloned by constructing a new D-arabitol utilization pathway in Escherichia coli. The C. albicans ArDH gene expressed in E. coli and Saccharomyces cerevisiae an enzyme that catalyzes the reaction D-arabitol + NAD <-->D-ribulose + NADH; this gene was present as a single copy per haploid genome, and its deduced peptide sequence was homologous with sequences of several members of the short-chain dehydrogenase family of enzymes. These results suggest that (i) C. albicans synthesizes D-arabitol by dephosphorylating and reducing the pentose pathway intermediate D-ribulose-5-PO4 and (ii) ArDH catalyzes the final step in this pathway.

Amino Acid Sequence↗
PubMed1994

Enzymes of glucose and methanol metabolism in the actinomycete Amycolatopsis methanolica.

The actinomycete Amycolatopsis methanolica was found to employ the normal bacterial set of glycolytic and pentose phosphate pathway enzymes, except for the presence of a PPi-dependent phosphofructokinase (PPi-PFK) and a 3-phosphoglycerate mutase that is stimulated by 2,3-bisphosphoglycerate. Screening of a number of actinomycetes revealed PPi-PFK activity only in members of the family Pseudonocardiaceae. The A. methanolica PPi-PFK and 3-phosphoglycerate mutase enzymes were purified to homogeneity. PPi-PFK appeared to be insensitive to the typical effectors of ATP-dependent PFK enzymes. Nevertheless, strong N-terminal amino acid sequence homology was found with ATP-PFK enzymes from other bacteria. The A. methanolica pyruvate kinase was purified over 250-fold and characterized as an allosteric enzyme, sensitive to inhibition by P(i) and ATP but stimulated by AMP. By using mutants, evidence was obtained for the presence of transketolase isoenzymes functioning in the pentose phosphate pathway and ribulose monophosphate cycle during growth on glucose and methanol, respectively.

Actinobacteria↗
PubMed1997

Ribose biosynthesis and evidence for an alternative first step in the common aromatic amino acid pathway in Methanococcus maripaludis.

An acetate-requiring mutant of Methanococcus maripaludis allowed efficient labeling of riboses following growth in minimal medium supplemented with [2-(13)C]acetate. Nuclear magnetic resonance and mass spectroscopic analysis of purified cytidine and uridine demonstrated that the C-1' of the ribose was about 67% enriched for 13C. This value was inconsistent with the formation of erythrose 4-phosphate (E4P) exclusively by the carboxylation of a triose. Instead, these results suggest that either (i) E4P is formed by both the nonoxidative pentose phosphate and triose carboxylation pathways or (ii) E4P is formed exclusively by the nonoxidative pentose phosphate pathway and is not a precursor of aromatic amino acids.

Acetates↗
PubMed2003

Responses of the central metabolism in Escherichia coli to phosphoglucose isomerase and glucose-6-phosphate dehydrogenase knockouts.

The responses of Escherichia coli central carbon metabolism to knockout mutations in phosphoglucose isomerase and glucose-6-phosphate (G6P) dehydrogenase genes were investigated by using glucose- and ammonia-limited chemostats. The metabolic network structures and intracellular carbon fluxes in the wild type and in the knockout mutants were characterized by using the complementary methods of flux ratio analysis and metabolic flux analysis based on [U-(13)C]glucose labeling and two-dimensional nuclear magnetic resonance (NMR) spectroscopy of cellular amino acids, glycerol, and glucose. Disruption of phosphoglucose isomerase resulted in use of the pentose phosphate pathway as the primary route of glucose catabolism, while flux rerouting via the Embden-Meyerhof-Parnas pathway and the nonoxidative branch of the pentose phosphate pathway compensated for the G6P dehydrogenase deficiency. Furthermore, additional, unexpected flux responses to the knockout mutations were observed. Most prominently, the glyoxylate shunt was found to be active in phosphoglucose isomerase-deficient E. coli. The Entner-Doudoroff pathway also contributed to a minor fraction of the glucose catabolism in this mutant strain. Moreover, although knockout of G6P dehydrogenase had no significant influence on the central metabolism under glucose-limited conditions, this mutation resulted in extensive overflow metabolism and extremely low tricarboxylic acid cycle fluxes under ammonia limitation conditions.

Citric Acid Cycle↗
PubMed1988

Biosynthesis of epsilon-rhodomycinone from glucose by Streptomyces C5 and comparison with intermediary metabolism of other polyketide-producing streptomycetes.

The catabolism of glucose by Streptomyces C5, a producer of anthracycline antibiotics, was investigated to determine the pathways that supply precursors for anthracycline biosynthesis. Carbons for the biosynthesis of epsilon-rhodomycinone, an anthracycline aglycone, from radiolabelled glucose were derived primarily from the Embden-Meyerhof-Parnas pathway, with a minor contribution from the pentose phosphate pathway. Furthermore, the anthracycline-producing strain, Streptomyces C5, as well as Streptomyces aureofaciens and Streptomyces lividans, strains that produce nonanthracycline polyketide antibiotics, displayed enzyme activities indicative of the Embden-Meyerhof-Parnas and pentose phosphate glycolytic pathways. As determined from labelling patterns, Streptomyces C5 apparently has a complete tricarboxylic acid cycle, but does not have a glyoxylate bypass pathway.

Anthracyclines↗
PubMed1989

Testing of the assumptions made in estimating the extent of futile cycling.

In estimating glucose and fructose 6-phosphate futile cycling in vivo, complete detritiation of [2-3H]glucose is assumed at the glucose 6-phosphate level, [3-3H]glucose at triose phosphate formation, and [6-3H]glucose in its conversion to glucose via pyruvate. [3-3H]glucose detritiation via the pentose cycle is assumed to be negligible. Normal and non-insulin-dependent diabetic subjects, in the basal state and infused with glucose, were given [2-3H,2-14C]galactose, and 3H-to-14C ratios in blood glucose were determined. [2-3H,2-14C]glucose was given with acetaminophen, and 3H/14C in urinary glucuronide was determined. Detritiation at glucose 6-phosphate was approximately 80%. [3-3H,1-14C]fructose was infused, and 3H/14C was determined in blood glucose and urinary glucuronide. At triose phosphate, 75-90% of the 3H was removed. The pentose cycle contribution was only a few percent. [6-3H,6-14C]glucose was infused, and 3H/14C in blood lactate was determined. [3-3H,3-14C]lactate was infused, and ratios in blood glucose were determined. Maximally, 10% of 3H from [6-3H]glucose was retained. If glucose and galactose are metabolized in the same hepatic site(s), glucose conversion to three-carbon intermediates in the indirect pathway of glycogen formation occurs in extrahepatic tissue(s). Reported estimates of futile cycling, although qualitatively correct, quantitatively require correction.

Adult↗
PubMed2005

Biosynthesis of ribose-5-phosphate and erythrose-4-phosphate in archaea: a phylogenetic analysis of archaeal genomes.

A phylogenetic analysis of the genes encoding enzymes in the pentose phosphate pathway (PPP), the ribulose monophosphate (RuMP) pathway, and the chorismate pathway of aromatic amino acid biosynthesis, employing data from 13 complete archaeal genomes, provides a potential explanation for the enigmatic phylogenetic patterns of the PPP genes in archaea. Genomic and biochemical evidence suggests that three archaeal species (Methanocaldococcus jannaschii, Thermoplasma acidophilum and Thermoplasma volcanium) produce ribose-5-phosphate via the nonoxidative PPP (NOPPP), whereas nine species apparently lack an NOPPP but may employ a reverse RuMP pathway for pentose synthesis. One species (Halobacterium sp. NRC-1) lacks both the NOPPP and the RuMP pathway but may possess a modified oxidative PPP (OPPP), the details of which are not yet known. The presence of transketolase in several archaeal species that are missing the other two NOPPP genes can be explained by the existence of differing requirements for erythrose-4-phosphate (E4P) among archaea: six species use transketolase to make E4P as a precursor to aromatic amino acids, six species apparently have an alternate biosynthetic pathway and may not require the ability to make E4P, and one species (Pyrococcus horikoshii) probably does not synthesize aromatic amino acids at all.

Amino Acids, Aromatic↗
PubMed2005

K-ras codon-specific mutations produce distinctive metabolic phenotypes in NIH3T3 mice [corrected] fibroblasts.

Among K-ras mutations, codon 12 mutations have been identified as those conferring a more aggressive phenotype. This aggressiveness is primarily associated with slow proliferation but greatly increased resistance to apoptosis. Using transfected NIH3T3 fibroblasts with a mutated K-ras minigene either at codon 12 (K12) or at codon 13 (K13), and taking advantage of [1,2-13C2]glucose tracer labeling, we show that codon 12 mutant K-ras (K12)-transformed cells exhibit greatly increased glycolysis with only a slight increase in activity along pathways that produce nucleic acid and lipid synthesis precursors in the oxidative branch of the pentose phosphate pathway and via pyruvate dehydrogenase flux. K13 mutants display a modest increase in anaerobic glycolysis associated with a large increase in oxidative pentose phosphate pathway activity and pyruvate dehydrogenase flux. The distinctive differences in metabolic profiles of K12 and K13 codon mutated cells indicate that a strong correlation exists between the flow of glucose carbons towards either increased anaerobic glycolysis, and resistance to apoptosis (K12), or increased macromolecule synthesis, rapid proliferation, and increased sensitivity to apoptosis.

Anaerobiosis↗
PubMed1991

Indices of oxidative stress in hamster lung following exposure to cobalt(II) ions: in vivo and in vitro studies.

Cobalt, a metal with numerous industrial applications, has been associated with lung disease, an extreme form of which is an interstitial fibrosis. The biochemical mechanisms underlying this toxicity are not understood. In vitro studies have suggested that cobalt(II) ions are able to generate reactive oxidant species (possibly hydroxyl radical) in a reaction with hydrogen peroxide, and we have hypothesized that the occurrence of such an event in lung tissue, and the subsequent development of oxidative damage, may contribute to this pulmonary toxicity. The intratracheal instillation of CoCl2 into hamster lungs resulted after 3 h in decreased levels of reduced glutathione and increases in levels of oxidized glutathione and in the activity of the pentose phosphate pathway. These changes, which are compatible with the generation of oxidative stress, were reversed by 48 h at low Co2+ doses (1.0 to 1,000 micrograms/kg). Irreversible changes at higher doses coincided with the onset of pulmonary edema. Incubation of lung slices with CoCl2 (0.1 to 10 mM) resulted in time- and Co2+ concentration-dependent increases in levels of oxidized glutathione and protein-mixed disulfides and a decrease in reduced glutathione. A concentration-dependent stimulation of the pentose phosphate pathway was also observed. These changes preceded the detection of overt cell toxicity, as assessed by various biochemical parameters. These data indicate that thiol oxidation constitutes an early event in the pulmonary toxicity of cobalt(II) ions and are compatible with the hypothesis that the generation of oxidative stress may be of significance to the toxic process.

Animals↗
PubMed2005

Mechanism responsible for the decreased hepatic NADPH generation rate in rats with bilateral ureter ligation-induced renal failure.

We previously reported that a decrease in hepatic NADPH generation results in reduced hepatic first-pass clearance of propranolol in rats with bilateral ureteral ligation (BUL)-induced renal failure. The aim of the present study was to evaluate the mechanisms responsible for the reduced NADPH generation in the supernatant of liver homogenates (SUP) obtained from rats with BUL. The NADPH generation in the SUP in the presence of NADP(+) was decreased in BUL rats as compared with control rats. After the addition of glucose-6-phosphate or 6-phosphogluconic acid, the increase in NADPH in the SUP of BUL rats was similar to that in control rats. The NADPH generation in the SUP after the addition of the ultrafiltrate of BUL rat SUP was smaller than that after the addition of the ultrafiltrate of control rat SUP. These findings suggest that the enzymatic activities in the pentose phosphate pathway were not decreased significantly in BUL rats, and that the decrease in the generation of NADPH in BUL rats was mainly caused by the decreased concentration of endogenous substrate(s) and/or the increased concentration of endogenous inhibitor(s) for the pentose phosphate pathway.

Acute Kidney Injury↗
PubMed2003

A possible role of NADPH-dependent cytochrome P450nor isozyme in glycolysis under denitrifying conditions.

The denitrifying fungus Cylindrocarpon tonkinense contains two isozymes of cytochrome P450nor. One isozyme, P450nor1, uses NADH specifically as its electron donor whereas the other isozyme P450nor2 prefers NADPH to NADH. Here we show that P450nor1 is localized in both cytosol and mitochondria, like P450nor of Fusarium oxysporum, while P450nor2 is exclusively in cytosol. We also found that the addition of glucose as a carbon source to the culture media leads to the production of much more P450nor2 in the fungal cells than a non-fermentable substrate (glycerol or acetate) does. These results suggest that the NADP-dependent pentose phosphate cycle acts predominantly in C. tonkinense as the glycolysis pathway under the denitrifying conditions, which was confirmed by the observation that glucose induced enzyme activities involved in the cycle. These results showed that P450nor2 should act as the electron sink under anaerobic, denitrifying conditions to regenerate NADP+ for the pentose phosphate cycle.

Ascomycota↗
PubMed2003

Radiation response of cells during altered protein thiol redox.

The major focus of this work was to investigate how altered protein thiol redox homeostasis affects radiation-induced cell death. We used the cells of wild-type CHO cell line K1, the CHO cell line E89, which is null for G6PD activity, and a radiation-sensitive CHO cell line, XRS5. The protein-thiol redox status of cells was altered with cell-permeable disulfides, hydroxyethyldisulfide (HEDS) or lipoate. HEDS is primarily reduced by thioltransferase (glutaredoxin), with GSH as the electron donor. In contrast, lipoate is reduced by thioredoxin reductase. HEDS was reduced at a greater rate than lipoate by G6PD-containing K1 (wild-type) cells. Reduction of disulfides by G6PD-deficient cells was significantly slower with HEDS as substrate and was nearly absent with lipoate. The rate of reduction of HEDS by E89 cells decelerated to near zero by 30 min, whereas the reduction continued at nearly the same rate during the entire measurement period for K1 cells. HEDS treatment decreased the GSH and protein thiol (PSH) content more in G6PD-deficient cells than in G6PD-containing cells. On the other hand, lipoate did not significantly alter the protein thiol, but it increased the GSH in K1 cells. Acute depletion of GSH by l-buthionine-sulfoximine (l-BSO) in combination with dimethylfumarate significantly decreased the rate of reduction of HEDS by K1 cells close to that of G6PD-deficient cells. Prior GSH depletion by l-BSO alone significantly decreased the PSH in glucose-depleted E89 cells exposed to HEDS, but this did not occur with K1 cells. The radiation response of G6PD-deficient cells was significantly sensitized by HEDS, but HEDS did not have this effect on K1 cells. The DNA repair-deficient XRS5 CHO cells displayed the same capacity as K1 cells for HEDS reduction, and like K1 cells the XRS5 cells were not sensitized to radiation by HEDS treatment. Deprivation of glucose, which provides the substrate for G6PD in the oxidative pentose phosphate cycle, decreased the rate of bioreduction of HEDS and lipoate in G6PD-containing cells to the level in G6PD-deficient cells. In the absence of glucose, HEDS treatment diminished non-protein thiol and protein thiol to the same level as those in G6PD-deficient cells and sensitized the K1 cells to HEDS treatment. However, depletion of glucose did not alter the sensitivity of XRS5 cells in either the presence or absence of HEDS. Overall the results suggest a major role for pentose cycle control of protein redox state coupled to the activities of the thioltransferase and thioredoxin systems. The results also show that protein thiol status is a critical factor in cell survival after irradiation.

Animals↗
PubMed2003

Metabolic biomarker and kinase drug target discovery in cancer using stable isotope-based dynamic metabolic profiling (SIDMAP).

Tumor cells respond to growth signals by the activation of protein kinases, altered gene expression and significant modifications in substrate flow and re-distribution among biosynthetic pathways. This results in a proliferating phenotype with altered cellular function. These transformed cells exhibit unique anabolic characteristics, which includes increased and preferential utilization of glucose through the non-oxidative steps of the pentose cycle for nucleic acid synthesis but limited de novo fatty acid synthesis and TCA cycle glucose oxidation. This primarily non-oxidative anabolic profile reflects an undifferentiated highly proliferative aneuploid cell phenotype and serves as a reliable metabolic biomarker to determine cell proliferation rate and the level of cell transformation/differentiation in response to drug treatment. Novel drugs effective in particular cancers exert their anti-proliferative effects by inducing significant reversions of a few specific non-oxidative anabolic pathways. Here we present evidence that cell transformation of various mechanisms is sustained by a unique disproportional substrate distribution between the two branches of the pentose cycle for nucleic acid synthesis, glycolysis and the TCA cycle for fatty acid synthesis and glucose oxidation. This can be demonstrated by the broad labeling and unique specificity of [1,2-(13)C(2)]glucose to trace a large number of metabolites in the metabolome. Stable isotope-based dynamic metabolic profiles (SIDMAP) serve the drug discovery process by providing a powerful new tool that integrates the metabolome into a functional genomics approach to developing new drugs. It can be used in screening kinases and their metabolic targets, which can therefore be more efficiently characterized, speeding up and improving drug testing, approval and labeling processes by saving trial and error type study costs in drug testing.

Biomarkers, Tumor↗