• Proceedings of the Korean Society of Plant Biotechnology Conference
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• 2005.11a
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• pp.411-411
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• 2005

• Biotechnology and Bioprocess Engineering:BBE
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• v.9 no.4
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• pp.252-255
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• 2004

A pfl ldhA double mutant Escherichia coli strain NZN 111 was used to produce succinic acid by overexpressing the E. coli malic enzyme gene (sfcA). This strain, however, produced a large amount of malic acid as well as succinic acid. After the analyses of the metabolic pathways, the fumB gene encoding the anaerobic fumarase of E. coli was co-amplified to solve the problem of malic acid accumulation. A plasmid, pTrcMLFu, was constructed, which contains an artificial operon (sfcA-fumB) under the control of the inducible trc promoter. From the batch culture of recombinant E. coli NZN 111 harboring pTrcMLFu, 7 g/L of succinic acid was produced from 20 g/L of glucose, with no accumulation of malic acid. From the metabolic flux analysis the strain was found under reducing power limiting conditions by severe reorientation of metabolic fluxes.

• BMB Reports
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• v.45 no.7
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• pp.396-401
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• 2012

Overnutrition is one of the major causes of non-alcoholic fatty liver disease (NAFLD). NAFLD is characterized by an accumulation of lipids (triglycerides) in hepatocytes and is often accompanied by high plasma levels of free fatty acids (FFA). In this study, we compared the energy metabolism in acute steatotic and non-steatotic primary mouse hepatocytes. Acute steatosis was induced by pre-incubation with high concentrations of oleate and palmitate. Labeling experiments were conducted using [$U-^{13}C_5$,$U-^{15}N_2$] glutamine. Metabolite concentrations and mass isotopomer distributions of intracellular metabolites were measured and applied for metabolic flux estimation using transient $^{13}C$ metabolic flux analysis. FFAs were efficiently taken up and almost completely incorporated into triglycerides (TAGs). In spite of high FFA uptake rates and the high synthesis rate of TAGs, central energy metabolism was not significantly changed in acute steatotic cells. Fatty acid ${\beta}$-oxidation does not significantly contribute to the detoxification of FFAs under the applied conditions.

• Journal of Microbiology and Biotechnology
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• v.9 no.5
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• pp.593-603
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• 1999

Poly(3-hydroxybutyrate) (PHB) production by fermentation was examined under both restricted- and ample-oxygen supply conditions in a single fed-batch fermentation. Recombinant Escherichia coli transformed with the PHB production plasmid pSYLl07 was grown to reach high cell density (227 g/l dry cell weight) with a high PHB content (78％ of dry cell weight), using a glucose-based minimal medium. A simple flux model containing 12 fluxes was developed and applied to the fermentation data. A superior closure (95％) of the carbon mass balance was achieved. When the data were put into use, the results demonstrated a surprisingly large excretion of formate and lactate. Even though periods of severe oxygen limitation coincided with rapid acetate and lactate excretion, PHB productivity and carbon utilization efficiency were not significantly impaired. These results are very positive in reducing oxygen demand in an industrial PHA fermentation without sacrificing its PHA productivity, thereby reducing overall production costs.

• Journal of Microbiology and Biotechnology
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• v.16 no.8
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• pp.1174-1179
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• 2006

The wild-type Corynebacterium glutamicum ATIC 13032 and Corynebacterium glutamicum ATTC 13032 lysC S301Y, exhibiting a deregulated aspartokinase, were compared concerning growth, lysine production, and intracellular carbon fluxes. Both strains differ by only one single nucleotide over the whole genome. In comparison to the wild-type, the mutant showed significant production of lysine with a molar yield of 0.087 mol (mol glucose$^{-1}$) whereas the biomass yield was reduced. The deregulation of aspartokinase further led to a global rearrangement of carbon flux throughout the whole central metabolism. This involved an increased flux through the pentose phosphate pathway (PPP) and an increased flux through anaplerosis. Because of this, the mutant revealed an enhanced supply of NADPH and oxaloacetate required for lysine biosynthesis. Additionally, the lumped flux through phosphoenolpyruvate carboxykinase and malic enzyme, withdrawing oxaloacetate back to the glycolysis and therefore detrimental for lysine production, was increased. The reason for this might be a contribution of malic enzyme to NADPH supply in the mutant in the mutant. The observed complex changes are remarkable, because they are due to the minimum genetic modification possible, the exchange of only one single nucleotide.

• Journal of Microbiology and Biotechnology
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• v.18 no.3
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• pp.532-538
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• 2008

For the newly isolated $H_2$-producing chemoheterotrophic bacterium Citrobacter amalonaticus Y19, anaerobic glucose metabolism was studied in batch cultivation at varying initial glucose concentrations (3.5-9.5 g/l). The carbon-mass and energy balances were determined and utilized to analyze the carbon metabolic-pathways network. The analyses revealed (a) variable production of major metabolites ($H_2$, ethanol, acetate, lactate, $CO_2$, and cell mass) depending on initial glucose levels; (b) influence of NADH regeneration on the production of acetate, lactate, and ethanol; and (c) influence of the molar production of ATP on the production of biomass. The results reported in this paper suggest how the carbon metabolic pathway(s) should be designed for optimal Hz production, especially at high glucose concentrations, such as by blocking the carbon flux via lactate dehydrogenase from the pyruvate node.

• Proceedings of the Korean Society for Bioinformatics Conference
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• 2004.11a
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• pp.39-49
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• 2004

When there is a lack of detailed kinetic information, dFBA(dynamic flux balance analysis) has correctly predicted cellular behavior under given environmental conditions with FBA and different ial equations. However, until now, dFBA has centered on substrate concentration, cell growth, and gene on/off, but a detailed hierarchical structure of a regulatory network has not been taken into account. For this reason, the dFBA has limited the represen tation of interactions between specific regulatory proteins and genes and the whole transcriptional regulation mechanism with environmental change. Moreover, to calculate optimal metabolic flux distribution which maximizes the growth flux and predict the b ehavior of cell system, linear programming package(LINDO) and spreadsheet package(EXCEL) have been used simultaneously. thses two software package have limited in the visual representation of simulation results and it can be difficult for a user to look at the effects of changing inputs to the models. Here, we descirbes the construction of hierarchical regulatory network with defined symbolsand the development of an integrated system that can predict the total control mechanism of regulatory elements (opero ns, genes, effectors, etc.), substrate concentration, growth rate, and optimal flux distribution with time. All programming procedures were accoplished in a visual programming environment (LabVIEW).

• 한국생물공학회:학술대회논문집
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• 2005.10a
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• pp.590-590
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• 2005

• 한국생물공학회:학술대회논문집
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• 2005.10a
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• pp.586-587
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• 2005

• Current Research on Agriculture and Life Sciences
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• v.32 no.4
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• pp.199-202
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• 2014

The bioconversion of cellulosic biomass hydrolyzates consisting mainly of glucose and xylose requires the use of engineered Saccharomyces cerevisiae expressing a heterologous xylose pathway. However, there is concern that a fungal xylose pathway consisting of NADPH-specific xylose reductase (XR) and $NAD^+$-specific xylitol dehydrogenase (XDH) may result in a cellular redox imbalance. However, the glycerol biosynthesis and glycerol degradation pathways of S. cerevisiae, termed here as the glycerol cycle, has the potential to balance the cofactor requirements for xylose metabolism, as it produces NADPH by consuming NADH at the expense of one mole of ATP. Therefore, this study tested if the glycerol cycle could improve the xylose metabolism of engineered S. cerevisiae by cofactor balancing, as predicted by an in-silico analysis using elementary flux mode (EFM). When the GPD1 gene, the first step of the glycerol cycle, was overexpressed in the XR/XDH-expressing S. cerevisiae, the glycerol production significantly increased, while the xylitol and ethanol yields became negligible. The reduced xylitol yield suggests that enough $NAD^+$ was supplied for XDH by the glycerol cycle. However, the GPD1 overexpression completely shifted the carbon flux from ethanol to glycerol. Thus, moderate expression of GPD1 may be necessary to achieve improved ethanol production through the cofactor balancing.