scholarly journals A Cyclic Metabolic Network inPseudomonas protegensPf-5 Prioritizes the Entner-Doudoroff Pathway and Exhibits Substrate Hierarchy during Carbohydrate Co-Utilization

2018 ◽  
Vol 85 (1) ◽  
Author(s):  
Rebecca A. Wilkes ◽  
Caroll M. Mendonca ◽  
Ludmilla Aristilde
Keyword(s):  
Metabolic Network ◽  
Carbohydrate Metabolism ◽  
Metabolic Flux ◽  
Gene Annotation ◽  
Pentose Phosphate ◽  
Flux Analysis ◽  
Environmental Matrices ◽  
Content Type ◽  
Phosphofructokinase Activity ◽  
Fructose 1,6 Bisphosphate

ABSTRACTThe genetic characterization ofPseudomonas protegensPf-5 was recently completed. However, the inferred metabolic network structure has not yet been evaluated experimentally. Here, we employed13C-tracers and quantitative flux analysis to investigate the intracellular network for carbohydrate metabolism. In lieu of the direct phosphorylation of glucose by glucose kinase, glucose catabolism was characterized primarily by the oxidation of glucose to gluconate and 2-ketogluconate before the phosphorylation of these metabolites to feed the Entner-Doudoroff (ED) pathway. In the absence of phosphofructokinase activity, a cyclic flux from the ED pathway to the upper Embden-Meyerhof-Parnas (EMP) pathway was responsible for routing glucose-derived carbons to the non-oxidative pentose phosphate (PP) pathway. Consistent with the lack of annotated genes inP. protegensPf-5 for the transport or initial catabolism of pentoses and galactose, only glucose was assimilated into intracellular metabolites in the presence of xylose, arabinose, or galactose. However, when glucose was fed simultaneously with fructose or mannose, co-uptake of these hexoses was evident, but glucose was preferred over fructose (3 to 1) and over mannose (4 to 1). Despite gene annotation of mannose catabolism to fructose-6-phosphate, metabolite labeling patterns revealed that mannose was assimilated into fructose-1,6-bisphosphate, similarly to fructose catabolism. Remarkably, carbons from mannose and fructose were also found to cycle backward through the upper EMP pathway toward the ED pathway. Therefore, the operational metabolic network for processing carbohydrates inP. protegensPf-5 prioritizes flux through the ED pathway to channel carbons to EMP, PP, and downstream pathways.IMPORTANCESpecies of thePseudomonasgenus thrive in various nutritional environments and have strong biocatalytic potential due to their diverse metabolic capabilities. Carbohydrate substrates are ubiquitous both in environmental matrices and in feedstocks for engineered bioconversion. Here, we investigated the metabolic network for carbohydrate metabolism inPseudomonas protegensPf-5. Metabolic flux quantitation revealed the relative involvement of different catabolic routes in channeling carbohydrate carbons through a cyclic metabolic network. We also uncovered that mannose catabolism was similar to fructose catabolism, despite the annotation of a different pathway in the genome. Elucidation of the constitutive metabolic network inP. protegensis important for understanding its innate carbohydrate processing, thus laying the foundation for targeting metabolic engineering of this untappedPseudomonasspecies.

scholarly journals Metabolic Flux Hierarchy Prioritizes the Entner-Doudoroff Pathway for Carbohydrate Co-Utilization inPseudomonas protegensPf-5

2018 ◽  
Author(s):  
Rebecca A. Wilkes ◽  
Caroll M. Mendonca ◽  
Ludmilla Aristilde
Keyword(s):  
Metabolic Network ◽  
Carbohydrate Metabolism ◽  
Metabolic Pathways ◽  
Metabolic Flux ◽  
Gene Annotation ◽  
Central Carbon Metabolism ◽  
Flux Analysis ◽  
Environmental Matrices ◽  
Fructose 1,6 Bisphosphate ◽  
Kinase Phosphorylation

ABSTRACTThe genetic characterization ofPseudomonas protegensPf-5 was recently completed. However, the inferred metabolic network structure has not yet been evaluated experimentally. Here we employed13C-tracers and quantitative flux analysis to investigate the intracellular network for carbohydrate metabolism. Similar to otherPseudomonasspecies,P. protegensPf-5 relied primarily on the Entner-Doudoroff (ED) pathway to connect initial glucose catabolism to downstream metabolic pathways. Flux quantitation determined that, in lieu of the direct phosphorylation of glucose by glucose kinase, phosphorylation of oxidized products of glucose (gluconate and 2-ketogluconate) towards the ED pathway accounted for over 90% of consumed glucose and greater than 35% of consumed glucose was secreted as gluconate and 2-ketogluconate. Consistent with the lack of annotated pathways for the initial catabolism of pentoses and galactose inP. protegensPf-5, only glucose was assimilated into intracellular metabolites in the presence of xylose, arabinose, or galactose. However, when glucose was fed simultaneously with fructose or mannose, co-uptake of the hexoses was evident but glucose was preferred over fructose (3 to 1) and over mannose (4 to 1). Despite gene annotation of mannose catabolism toward fructose 6-phosphate, metabolite labeling patterns revealed that mannose-derived carbons specifically entered central carbon metabolism via fructose-1,6-bisphosphate, similarly to fructose catabolism. Remarkably, carbons from mannose and fructose were found to cycle backward through the upper Emden-Meyerhof-Parnas pathway to feed into the ED pathway. Therefore, the operational metabolic network for processing carbohydrates inP. protegensPf-5 prioritizes flux through the ED pathway to channel carbons to downstream metabolic pathways.IMPORTANCESpecies of thePseudomonasgenus thrive in various nutritional environments and have strong biocatalytic potential due to their diverse metabolic capabilities. Carbohydrate substrates are ubiquitous both in environmental matrices and in feedstocks for engineered bioconversion. Here we investigated the metabolic network for carbohydrate metabolism inP. protegensPf-5. Metabolic flux quantitation revealed the relative involvement of different catabolic routes in channeling carbohydrate carbons through the network. We also uncovered that mannose catabolism was similar to fructose catabolism, despite the gene annotation of two different pathways in the genome. Elucidation of the constitutive metabolic network inP. protegensis important for understanding its innate carbohydrate processing, thus laying the foundation for targeting metabolic engineering of this untappedPseudomonasspecies.

scholarly journals The Entner-Doudoroff and Nonoxidative Pentose Phosphate Pathways Bypass Glycolysis and the Oxidative Pentose Phosphate Pathway in Ralstonia solanacearum

mSystems ◽  
2020 ◽  
Vol 5 (2) ◽  
Author(s):  
Poonam Jyoti ◽  
Manu Shree ◽  
Chandrakant Joshi ◽  
Tulika Prakash ◽  
Suvendra Kumar Ray ◽  
...  
Keyword(s):  
Network Analysis ◽  
Metabolic Network ◽  
Pentose Phosphate Pathway ◽  
Ralstonia Solanacearum ◽  
Metabolic Flux ◽  
Pentose Phosphate ◽  
Flux Analysis ◽  
Content Type ◽  
Metabolic Network Analysis ◽  
Balance Analysis

ABSTRACT In Ralstonia solanacearum, a devastating phytopathogen whose metabolism is poorly understood, we observed that the Entner-Doudoroff (ED) pathway and nonoxidative pentose phosphate pathway (non-OxPPP) bypass glycolysis and OxPPP under glucose oxidation. Evidence derived from 13C stable isotope feeding and genome annotation-based comparative metabolic network analysis supported the observations. Comparative metabolic network analysis derived from the currently available 53 annotated R. solanacearum strains, including a recently reported strain (F1C1), representing the four phylotypes, confirmed the lack of key genes coding for phosphofructokinase (pfk-1) and phosphogluconate dehydrogenase (gnd) enzymes that are relevant for glycolysis and OxPPP, respectively. R. solanacearum F1C1 cells fed with [13C]glucose (99% [1-13C]glucose or 99% [1,2-13C]glucose or 40% [13C6]glucose) followed by gas chromatography-mass spectrometry (GC-MS)-based labeling analysis of fragments from amino acids, glycerol, and ribose provided clear evidence that rather than glycolysis and the OxPPP, the ED pathway and non-OxPPP are the main routes sustaining metabolism in R. solanacearum. The 13C incorporation in the mass ions of alanine (m/z 260 and m/z 232), valine (m/z 288 and m/z 260), glycine (m/z 218), serine (m/z 390 and m/z 362), histidine (m/z 440 and m/z 412), tyrosine (m/z 466 and m/z 438), phenylalanine (m/z 336 and m/z 308), glycerol (m/z 377), and ribose (m/z 160) mapped the pathways supporting the observations. The outcomes help better define the central carbon metabolic network of R. solanacearum that can be integrated with 13C metabolic flux analysis as well as flux balance analysis studies for defining the metabolic phenotypes. IMPORTANCE Understanding the metabolic versatility of Ralstonia solanacearum is important, as it regulates the trade-off between virulence and metabolism (1, 2) in a wide range of plant hosts. Due to a lack of clear evidence until this work, several published research papers reported on the potential roles of glycolysis and the oxidative pentose phosphate pathway (OxPPP) in R. solanacearum (3, 4). This work provided evidence from 13C stable isotope feeding and genome annotation-based comparative metabolic network analysis that the Entner-Doudoroff pathway and non-OxPPP bypass glycolysis and OxPPP during the oxidation of glucose, a component of the host xylem pool that serves as a potential carbon source (5). The outcomes help better define the central carbon metabolic network of R. solanacearum that can be integrated with 13C metabolic flux analysis as well as flux balance analysis studies for defining the metabolic phenotypes. The study highlights the need to critically examine phytopathogens whose metabolism is poorly understood.

scholarly journals Metabolic Fluxes in Corynebacterium glutamicum during Lysine Production with Sucrose as Carbon Source

2004 ◽  
Vol 70 (12) ◽  
pp. 7277-7287 ◽  
Author(s):  
Christoph Wittmann ◽  
Patrick Kiefer ◽  
Oskar Zelder
Keyword(s):  
Carbon Source ◽  
Corynebacterium Glutamicum ◽  
Metabolic Flux ◽  
Tca Cycle ◽  
Pentose Phosphate ◽  
Flux Analysis ◽  
Phosphotransferase System ◽  
Lysine Production ◽  
Metabolic Fluxes ◽  
Fructose 1,6 Bisphosphate

ABSTRACT Metabolic fluxes in the central metabolism were determined for lysine-producing Corynebacterium glutamicum ATCC 21526 with sucrose as a carbon source, providing an insight into molasses-based industrial production processes with this organism. For this purpose, 13C metabolic flux analysis with parallel studies on [1-13CFru]sucrose, [1-13CGlc]sucrose, and [13C6 Fru]sucrose was carried out. C. glutamicum directed 27.4% of sucrose toward extracellular lysine. The strain exhibited a relatively high flux of 55.7% (normalized to an uptake flux of hexose units of 100%) through the pentose phosphate pathway (PPP). The glucose monomer of sucrose was completely channeled into the PPP. After transient efflux, the fructose residue was mainly taken up by the fructose-specific phosphotransferase system (PTS) and entered glycolysis at the level of fructose-1,6-bisphosphate. Glucose-6-phosphate isomerase operated in the gluconeogenetic direction from fructose-6-phosphate to glucose-6-phosphate and supplied additional carbon (7.2%) from the fructose part of the substrate toward the PPP. This involved supply of fructose-6-phosphate from the fructose part of sucrose either by PTSMan or by fructose-1,6-bisphosphatase. C. glutamicum further exhibited a high tricarboxylic acid (TCA) cycle flux of 78.2%. Isocitrate dehydrogenase therefore significantly contributed to the total NADPH supply of 190%. The demands for lysine (110%) and anabolism (32%) were lower than the supply, resulting in an apparent NADPH excess. The high TCA cycle flux and the significant secretion of dihydroxyacetone and glycerol display interesting targets to be approached by genetic engineers for optimization of the strain investigated.

scholarly journals Combined Fluxomics and Transcriptomics Analysis of Glucose Catabolism via a Partially Cyclic Pentose Phosphate Pathway in Gluconobacter oxydans 621H

2013 ◽  
Vol 79 (7) ◽  
pp. 2336-2348 ◽  
Author(s):  
Tanja Hanke ◽  
Katharina Nöh ◽  
Stephan Noack ◽  
Tino Polen ◽  
Stephanie Bringer ◽  
...  
Keyword(s):  
Phase Ii ◽  
Growth Phase ◽  
Pentose Phosphate Pathway ◽  
Metabolic Flux ◽  
Glucose Dehydrogenase ◽  
Gluconobacter Oxydans ◽  
Pentose Phosphate ◽  
Flux Analysis ◽  
Content Type ◽  
Activity Measurements

ABSTRACTIn this study, the distribution and regulation of periplasmic and cytoplasmic carbon fluxes inGluconobacter oxydans621H with glucose were studied by13C-based metabolic flux analysis (13C-MFA) in combination with transcriptomics and enzyme assays. For13C-MFA, cells were cultivated with specifically13C-labeled glucose, and intracellular metabolites were analyzed for their labeling pattern by liquid chromatography-mass spectrometry (LC-MS). In growth phase I, 90% of the glucose was oxidized periplasmically to gluconate and partially further oxidized to 2-ketogluconate. Of the glucose taken up by the cells, 9% was phosphorylated to glucose 6-phosphate, whereas 91% was oxidized by cytoplasmic glucose dehydrogenase to gluconate. Additional gluconate was taken up into the cells by transport. Of the cytoplasmic gluconate, 70% was oxidized to 5-ketogluconate and 30% was phosphorylated to 6-phosphogluconate. In growth phase II, 87% of gluconate was oxidized to 2-ketogluconate in the periplasm and 13% was taken up by the cells and almost completely converted to 6-phosphogluconate. SinceG. oxydanslacks phosphofructokinase, glucose 6-phosphate can be metabolized only via the oxidative pentose phosphate pathway (PPP) or the Entner-Doudoroff pathway (EDP).13C-MFA showed that 6-phosphogluconate is catabolized primarily via the oxidative PPP in both phases I and II (62% and 93%) and demonstrated a cyclic carbon flux through the oxidative PPP. The transcriptome comparison revealed an increased expression of PPP genes in growth phase II, which was supported by enzyme activity measurements and correlated with the increased PPP flux in phase II. Moreover, genes possibly related to a general stress response displayed increased expression in growth phase II.

scholarly journals Comparative13C Metabolic Flux Analysis of Pyruvate Dehydrogenase Complex-Deficient, l-Valine-Producing Corynebacterium glutamicum

2011 ◽  
Vol 77 (18) ◽  
pp. 6644-6652 ◽  
Author(s):  
Tobias Bartek ◽  
Bastian Blombach ◽  
Siegmund Lang ◽  
Bernhard J. Eikmanns ◽  
Wolfgang Wiechert ◽  
...  
Keyword(s):  
Pyruvate Dehydrogenase ◽  
Metabolic Flux Analysis ◽  
Metabolic Flux ◽  
Pyruvate Dehydrogenase Complex ◽  
Pentose Phosphate ◽  
Strong Increase ◽  
Flux Analysis ◽  
Wild Type ◽  
Content Type ◽  
Split Ratio

ABSTRACTl-Valine can be formed successfully usingC. glutamicumstrains missing an active pyruvate dehydrogenase enzyme complex (PDHC). Wild-typeC. glutamicumand four PDHC-deficient strains were compared by13C metabolic flux analysis, especially focusing on the split ratio between glycolysis and the pentose phosphate pathway (PPP). Compared to the wild type, showing a carbon flux of 69% ± 14% through the PPP, a strong increase in the PPP flux was observed in PDHC-deficient strains with a maximum of 113% ± 22%. The shift in the split ratio can be explained by an increased demand of NADPH forl-valine formation. In accordance, the introduction of theEscherichia colitranshydrogenase PntAB, catalyzing the reversible conversion of NADH to NADPH, into anl-valine-producingC. glutamicumstrain caused the PPP flux to decrease to 57% ± 6%, which is below the wild-type split ratio. Hence, transhydrogenase activity offers an alternative perspective for sufficient NADPH supply, which is relevant for most amino acid production systems. Moreover, as demonstrated forl-valine, this bypass leads to a significant increase of product yield due to a concurrent reduction in carbon dioxide formation via the PPP.

scholarly journals Entner–Doudoroff pathway and Non-OxPPP bypasses glycolysis and OxPPP in Ralstonia solanacearum

2020 ◽  
Author(s):  
Poonam Jyoti ◽  
Manu Shree ◽  
Chandrakant Joshi ◽  
Tulika Prakash ◽  
Suvendra Kumar Ray ◽  
...  
Keyword(s):  
Network Analysis ◽  
Metabolic Network ◽  
Ralstonia Solanacearum ◽  
Metabolic Flux ◽  
Pentose Phosphate ◽  
Flux Analysis ◽  
Flux Balance ◽  
Metabolic Network Analysis ◽  
Central Carbon ◽  
Balance Analysis

AbstractIn Ralstonia solanacearum, a devastating phytopathogen whose metabolism is poorly understood, we observed that Entner-Doudoroff (ED) pathway and NonOxidative pentose phosphate pathway (OxPPP) bypasses glycolysis and OxPPP under glucose oxidation. Evidences derived from 13C stable isotopes feeding and genome annotation based comparative metabolic network analysis supported the observations. Comparative metabolic network analysis derived from the currently available 53 annotated R. solanacearum strains also including the recently reported strain (F1C1), representing the four phylotypes confirmed the lack of key genes coding for phosphofructokinase (pfk-1) and phosphogluconate dehydrogenase (gnd) enzymes that are relevant for glycolysis and OxPPP respectively. R. solanacearum F1C1 cells fed with 13C Glucose (99%[1-13C]- or 99%[1,2-13C]- or 40%[13C6]-glucose) followed by GC-MS based labelling analysis of fragments from amino acids, glycerol and ribose provided clear evidence that rather than Glycolysis and OxPPP, ED pathway and NonOxPPP are the main routes sustaining metabolism in R. solanacearum. The 13C incorporation in the mass ions of alanine (m/z 260, m/z 232); valine (m/z 288, m/z 260), glycine (m/z 218), serine (m/z 390, m/z 362), histidine (m/z 440, m/z 412), tyrosine (m/z 466, m/z 438), phenylalanine (m/z 336, m/z 308), glycerol (m/z 377) and ribose (m/z 160) mapped the pathways supporting the observations. The outcomes help better defining the central carbon metabolic network of R. solanacearum that can be integrated with 13C metabolic flux analysis as well as flux balance analysis studies for defining the metabolic phenotypes.ImportanceUnderstanding the metabolic versatility of Ralstonia solanacearum is important as it regulates the tradeoff between virulence and metabolism (1, 2) in a wide range of plant hosts. Due to a lack of clear evidence until this work, several published research papers reported on potential roles of Glycolysis and Oxidative pentose phosphate pathways (OxPPP) in R. solanacearum (3, 4). This work provided evidence from 13C stable isotopes feeding and genome annotation based comparative metabolic network analysis that Entner-Doudoroff pathway and Non-OxPPP bypasses glycolysis and OxPPP during the oxidation of Glucose, one of the host xylem pool that serves as a potential carbon source (5). The outcomes help better defining the central carbon metabolic network of R. solanacearum that can be integrated with 13C metabolic flux analysis as well as flux balance analysis studies for defining the metabolic phenotypes. The study highlights the need to critically examine phytopathogens whose metabolism is poorly understood.

68 Flux analysis of aerobic glycolysis in bovine blastocysts and CT1 cells

2019 ◽  
Vol 31 (1) ◽  
pp. 159
Author(s):  
J. Chung ◽  
R. Clifford ◽  
G. Sriram ◽  
C. Keefer
Keyword(s):  
Mass Spectrometry ◽  
Gas Chromatography ◽  
Metabolic Flux ◽  
Aerobic Glycolysis ◽  
Carbon Sources ◽  
Pentose Phosphate ◽  
Gas Chromatography Mass Spectrometry ◽  
Flux Analysis ◽  
Metabolic Modelling ◽  
Chromatography Mass Spectrometry

Embryo quality and maternal recognition are crucial for successful initiation of bovine pregnancy. Previous studies have proposed that better quality embryos use aerobic glycolysis to meet a high demand for biomass components. While hexoses are the principal carbon sources that provide energy to glycolysis, little is known about partitioning of hexoses into metabolic pathways or alteration of partitioning when different hexoses are simultaneously available. Specific metabolic utilisation of 13C-labelled substrates can be quantified by gas chromatography-mass spectrometry, an excellent noninvasive approach for studying cellular metabolism. To assess hexose flux through central metabolism, bovine blastocysts and CT1 cells (a bovine trophectoderm cell line) were cultured in SOF-based media supplemented with combinations of 50% uniformly labelled (U) and 50% naturally abundant (NA) glucose (Glc) or fructose (Fru) (U−13C Glc+NA Glc, U−13C Fru+NA Fru, U−13C Glc+NA Fru, and U−13C Fru+NA Glc), such that total hexose concentration was 1.5mM. Metabolites in spent media from 24-h cultures of single or 5 blastocysts (40-μL drops; 5% CO2, 5% O2, 90% N2) and 1-, 2-, 3-, 6-, 8-, and 24-h incubations of CT1 cells (150 μL; ~3×104 cells per well; 5% CO2, 95% air) were extracted with a MeOH-CHCl3 reagent, derivatized, and analysed by gas chromatography-mass spectrometry. Measurement of mass isotopomer distributions of metabolites, chiefly pyruvate, lactate, and amino acids, followed by correction for natural abundances and metabolic modelling, revealed several insights. For instance, five Day 7 or Day 8 blastocysts (Day 0=fertilization) supplied with U−13C Glc+NA Fru displayed 13C enrichments of 80.3%±1.4% for pyruvate and 71.6%±2.8% for lactate, whereas when supplied with U−13C Fru+NA Glc, they displayed lower 13C enrichments of 5.7%±2.4% for pyruvate and 2.8%±0.4% lactate (mean±standard deviation, n=3 to 4). Metabolic modelling revealed that when Glc and Fru are simultaneously available, the blastocysts used 2.5±0.2 moles of Fru per 100 moles of Glc used. Furthermore, 13C enrichment of pyruvate was 42.0±0.6% when U−13C Glc+NA Glc was supplied and 37.8±2.7% when U−13C Fru+NA Fru was supplied. Lactate enrichments followed a similar trend. This indicates that, individually, Glc and Fru were utilised majorly through aerobic glycolysis with some involvement of the pentose phosphate pathway. Alanine was negligibly labelled in all of the experiments, suggesting either a low TCA flux or that alanine is diluted by extra- or intracellular amino or fatty acids. Single blastocysts and CT1 cells showed a similar labelling pattern when hexoses were available. Following Glc depletion at 8h in CT1 cultures, the 13C enrichments of alanine and citrate in the media increased, suggesting a sharp alteration of metabolic state. These findings demonstrate that metabolic flux can be comprehensively analysed for single bovine blastocysts and CT1 cell metabolism models that of the blastocyst. This project was supported by Agriculture and Food Research Initiative Competitive Grant no. 2015-67015-23237 from the USDA National Institute of Food and Agriculture.

scholarly journals 472 Effects of Low-temperature Storage on Carbohydrate Metabolism in Potato Tubers

HortScience ◽  
1999 ◽  
Vol 34 (3) ◽  
pp. 526B-526 ◽  
Author(s):  
Robert W. Blenkinsop ◽  
Leslie J. Copp ◽  
Alejandro G. Marangoni ◽  
Rickey Y. Yada
Keyword(s):  
Low Temperature ◽  
Metabolic Rate ◽  
Carbohydrate Metabolism ◽  
Potato Chip ◽  
Anaerobic Respiration ◽  
Pentose Phosphate ◽  
Potato Tubers ◽  
Low Temperature Storage ◽  
C Storage ◽  
Phosphofructokinase Activity

Following exposure to low temperatures (i.e., <10 °C), potato tubers undergo low-temperature sweetening (LTS), the conversion of starch to sugars. This phenomenon is of great importance to potato chip processors because high levels of reducing sugars lead to undesirable nonenzymatic browning during potato chip frying operations. The purpose of this study was to elucidate the biochemical differences in carbohydrate metabolism between a tolerant (ND 860-2) and a sensitive (Novachip) cultivar during 4 °C storage. On chilling, there was an increase in the levels of sucrose, fructose, and glucose in both cultivars, with levels being at least 2-fold higher in the sensitive cultivar. Increased levels of ATP and NADH, along with a higher respiratory rate observed in the tolerant tubers, collectively indicate a higher metabolic rate in the LTS-tolerant cultivar. ATP- and pyrophosphate-dependent phosphofructokinase activity was similar in both cultivars. Higher levels of ethanol and lactate were also observed in ND 860-2, suggesting a greater flux of sugars via anaerobic respiration. No significant differences were observed in enzymatic activities in the oxidative pentose phosphate pathway (PPP) or in levels of NADPH, thereby suggesting that the PPP does not play a role in conferring LTS tolerance. Therefore, we propose that LTS-tolerant potatoes may maintain low tissue sugar concentrations via an overall increased metabolism, rather than differing in one specific metabolic step. This increased metabolic rate does not appear to be due to greater enzyme expression (i.e., coarse control) but, rather, to a greater overall flux of carbohydrates through glycolysis and respiration.

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