Aerobic Glucose Catabolism Research Articles

Inducible Systemic Gcn1 Deletion in Mice Leads to Transient Body Weight Loss upon Tamoxifen Treatment Associated with Decrease of Fat and Liver Glycogen Storage.

GCN1 is an evolutionarily-conserved ribosome-binding protein that mediates the amino acid starvation response as well as the ribotoxic stress response. We previously demonstrated that Gcn1 mutant mice lacking the GCN2-binding domain suffer from growth retardation and postnatal lethality via GCN2-independent mechanisms, while Gcn1-null mice die early in embryonic development. In this study, we explored the role of GCN1 in adult mice by generating tamoxifen-inducible conditional knockout (CKO) mice. Unexpectedly, the Gcn1 CKO mice showed body weight loss during tamoxifen treatment, which gradually recovered following its cessation. They also showed decreases in liver weight, hepatic glycogen and lipid contents, blood glucose and non-esterified fatty acids, and visceral white adipose tissue weight with no changes in food intake and viability. A decrease of serum VLDL suggested that hepatic lipid supply to the peripheral tissues was primarily impaired. Liver proteomic analysis revealed the downregulation of mitochondrial β-oxidation that accompanied increases of peroxisomal β-oxidation and aerobic glucose catabolism that maintain ATP levels. These findings show the involvement of GCN1 in hepatic lipid metabolism during tamoxifen treatment in adult mice.

Cyclic AMP-Dependent Catabolite Repression Is the Dominant Control Mechanism of Metabolic Fluxes under Glucose Limitation in Escherichia coli

Although a whole arsenal of mechanisms are potentially involved in metabolic regulation, it is largely uncertain when, under which conditions, and to which extent a particular mechanism actually controls network fluxes and thus cellular physiology. Based on (13)C flux analysis of Escherichia coli mutants, we elucidated the relevance of global transcriptional regulation by ArcA, ArcB, Cra, CreB, CreC, Crp, Cya, Fnr, Hns, Mlc, OmpR, and UspA on aerobic glucose catabolism in glucose-limited chemostat cultures at a growth rate of 0.1 h(-1). The by far most relevant control mechanism was cyclic AMP (cAMP)-dependent catabolite repression as the inducer of the phosphoenolpyruvate (PEP)-glyoxylate cycle and thus low tricarboxylic acid cycle fluxes. While all other mutants and the reference E. coli strain exhibited high glyoxylate shunt and PEP carboxykinase fluxes, and thus high PEP-glyoxylate cycle flux, this cycle was essentially abolished in both the Crp and Cya mutants, which lack the cAMP-cAMP receptor protein complex. Most other mutations were phenotypically silent, and only the Cra and Hns mutants exhibited slightly altered flux distributions through PEP carboxykinase and the tricarboxylic acid cycle, respectively. The Cra effect on PEP carboxykinase was probably the consequence of a specific control mechanism, while the Hns effect appears to be unspecific. For central metabolism, the available data thus suggest that a single transcriptional regulation process exerts the dominant control under a given condition and this control is highly specific for a single pathway or cycle within the network.

Impact of global transcriptional regulation by ArcA, ArcB, Cra, Crp, Cya, Fnr, and Mlc on glucose catabolism in Escherichia coli.

Even though transcriptional regulation plays a key role in establishing the metabolic network, the extent to which it actually controls the in vivo distribution of metabolic fluxes through different pathways is essentially unknown. Based on metabolism-wide quantification of intracellular fluxes, we systematically elucidated the relevance of global transcriptional regulation by ArcA, ArcB, Cra, Crp, Cya, Fnr, and Mlc for aerobic glucose catabolism in batch cultures of Escherichia coli. Knockouts of ArcB, Cra, Fnr, and Mlc were phenotypically silent, while deletion of the catabolite repression regulators Crp and Cya resulted in a pronounced slow-growth phenotype but had only a nonspecific effect on the actual flux distribution. Knockout of ArcA-dependent redox regulation, however, increased the aerobic tricarboxylic acid (TCA) cycle activity by over 60%. Like aerobic conditions, anaerobic derepression of TCA cycle enzymes in an ArcA mutant significantly increased the in vivo TCA flux when nitrate was present as an electron acceptor. The in vivo and in vitro data demonstrate that ArcA-dependent transcriptional regulation directly or indirectly controls TCA cycle flux in both aerobic and anaerobic glucose batch cultures of E. coli. This control goes well beyond the previously known ArcA-dependent regulation of the TCA cycle during microaerobiosis.

Cofactor engineering: a novel approach to metabolic engineering in Lactococcus lactis by controlled expression of NADH oxidase.

NADH oxidase-overproducing Lactococcus lactis strains were constructed by cloning the Streptococcus mutans nox-2 gene, which encodes the H2O-forming NADH oxidase, on the plasmid vector pNZ8020 under the control of the L. lactis nisA promoter. This engineered system allowed a nisin-controlled 150-fold overproduction of NADH oxidase at pH 7.0, resulting in decreased NADH/NAD ratios under aerobic conditions. Deliberate variations on NADH oxidase activity provoked a shift from homolactic to mixed-acid fermentation during aerobic glucose catabolism. The magnitude of this shift was directly dependent on the level of NADH oxidase overproduced. At an initial growth pH of 6.0, smaller amounts of nisin were required to optimize NADH oxidase overproduction, but maximum NADH oxidase activity was twofold lower than that found at pH 7.0. Nonetheless at the highest induction levels, levels of pyruvate flux redistribution were almost identical at both initial pH values. Pyruvate was mostly converted to acetoin or diacetyl via alpha-acetolactate synthase instead of lactate and was not converted to acetate due to flux limitation through pyruvate dehydrogenase. The activity of the overproduced NADH oxidase could be increased with exogenously added flavin adenine dinucleotide. Under these conditions, lactate production was completely absent. Lactate dehydrogenase remained active under all conditions, indicating that the observed metabolic effects were only due to removal of the reduced cofactor. These results indicate that the observed shift from homolactic to mixed-acid fermentation under aerobic conditions is mainly modulated by the level of NADH oxidation resulting in low NADH/NAD+ ratios in the cells.

Anaerobic metabolism in aerobic mammalian cells: information from the ratio of calorimetric heat flux and respirometric oxygen flux

Calorimetric and respirometric studies of cultured cells show that both neoplastic and non-neoplastic cell types maintain an anaerobic contribution to their total heat flux. In many mammalian cells this can be explained quantitatively by lactate production observed under fully aerobic conditions. Uncoupling and enhanced futile substrate cycling increase the ratio of heat flux to oxygen flux, the calorimetric-respirometric (CR) ratio. The interpretation of calorimetric and respirometric measurements requires an energy balance approach in which experimentally measured CR ratios are compared with thermochemically derived oxycaloric equivalents. The oxycaloric equivalent is the enthalpy change per mole of oxygen consumed, and equals −470 kJ / mol O 2 in the aerobic catabolism of glucose, assuming that catabolism is 100% dissipative (the net efficiency of metabolic heat transformation is zero). CR ratios more negative than −470 kJ / mol O 2 have been reported in well-oxygenated cell cultures and are discussed in terms of integrated aerobic and anaerobic metabolism.

Calorimetric measurement of the effect of pH on the anaerobic and aerobic catabolism of glucose by Streptococcus agalactiae.

Calorimetric measurement of the effect of pH on the anaerobic and aerobic catabolism of glucose by Streptococcus agalactiae.

Testicular Metabolism in Adrenalectomized and Corticosterone Treated Rats

SummaryTesticular metabolism was examined after adult rats were adrenalectom-ized and/or treated with corticosterone (0.7S, 1.5, and 3.0 mg/day) for 5 days. The weight and DNA and RNA concentrations of testes were not affected by either adrenalectomy or corticosterone replacement but corticosterone (3.0 mg) reduced (p<0.05) testis protein and prevented the loss of testis carbohydrate noted after adrenalectomy. Anaerobic glucose catabolism (cell-free preparations) increased 12% (p<0.05) after adrenalectomy and decreased 13% (p<0.05) after corticosterone (3.0 mg) therapy but neither of these treatments affected aerobic glucose catabolism. Corticosterone (3.0 mg) depressed (p<0.05) the oxidation of glucose-1-14C and glucose-6-14C to 14CO2; whereas adrenalectomy showed a tendency to increase the activity of 14CO2. Testosterone synthesis dropped (p<0.05) after corticosterone (3.0 mg) therapy but was not altered by adrenalectomy. The results suggest that adrenalectomy modifies testicular glucose ca-tabolism and...

Effects of colicins E1 and K on cellular metabolism.

Colicins E1 and K inhibited a whole series of energy-dependent reactions in Escherichia coli cells, including motility, biosynthesis of nucleic acids, proteins and polysaccharides, and the conversion of ornithine to citrulline. Respiration was only partially affected, and substrates such as glucose continued to be catabolized through the normal pathways, albeit with reduced CO(2) production. The soluble products of aerobic glucose catabolism by colicin-treated cells were analyzed. Pyruvate replaced acetate as the major excreted product, and the following intermediates of glycolysis were excreted in significant amounts: glucose-6-phosphate, fructose-1,6-diphosphate, dihydroxyacetone phosphate, and 3-phosphoglycerate. Anaerobically growing cells manifested a somewhat enhanced tolerance to the colicins. This protection by anaerobiosis appeared to depend on the exclusion of oxygen more than on the extent of fermentative catabolism versus catabolism of the respiratory type. These results are interpreted in terms of possible functions of colicin in lowering the adenosine triphosphate (ATP) content of the cells and in terms of the role of lowered ATP levels in inhibiting many of the energy-requiring reactions.

Carbon Dioxide Effects on Glucose Catabolism by Mixed Microbial Cultures

Results have shown that, with mixed culture (sewage) inocula, the lag period in aerobic catabolism of glucose can be reduced by increased CO 2 tension. Conversely, removal of CO 2 from the air supply to the growth flasks and Warburg vessels may increase the lag period.

Carbon Dioxide Effects on Glucose Catabolism by Mixed Microbial Cultures1

Results have shown that, with mixed culture (sewage) inocula, the lag period in aerobic catabolism of glucose can be reduced by increased CO(2) tension. Conversely, removal of CO(2) from the air supply to the growth flasks and Warburg vessels may increase the lag period.

FORMATION OF VALINE BY STREPTOMYCIN-DEPENDENT ESCHERICHIA COLI.

Bragg, P. D. (University of British Columbia, Vancouver, British Columbia, Canada), and W. J. Polglase. Formation of valine by streptomycin-dependent Escherichia coli. J. Bacteriol. 88:1006-1009. 1964.-The primary extracellular products of the aerobic catabolism of glucose in streptomycin-dependent Escherichia coli were found to be carbon dioxide and acetate, the ratio of these two products being dependent on the rate of aeration but independent of antibiotic. Secondary extracellular products of dependent E. coli were valine and lactic acid; the former was produced in the presence of antibiotic under aerobic conditions, and the latter metabolite was formed under conditions of either antibiotic depletion or oxygen deprivation. The fact that the same products were formed when either streptomycin or oxygen was limiting supports the hypothesis that the antibiotic is required to complete hydrogen transport in dependent E. coli. The formation of valine appears to represent an anomalous pathway of aerobic glucose catabolism, whereby a neutral, relatively highly reduced end product is excreted.