scholarly journals Supply and consumption of glucose 6-phosphate in the chloroplast stroma

2018 ◽  
Author(s):  
Alyssa L. Preiser ◽  
Aparajita Banerjee ◽  
Nicholas Fisher ◽  
Thomas D. Sharkey
Keyword(s):  
Redox Regulation ◽  
Alternative Pathway ◽  
Starch Synthesis ◽  
Significant Activity ◽  
High Concentration ◽  
Futile Cycle ◽  
Reducing Conditions ◽  
Futile Cycling ◽  
Chloroplast Stroma ◽  
Glucose 6 Phosphate Dehydrogenase

AbstractFructose 6-phosphate is an intermediate in the Calvin-Benson cycle and can be acted on by phosphoglucoisomerase to make glucose 6-phosphate (G6P) for starch synthesis. A high concentration of G6P is favorable for starch synthesis but can also stimulate G6P dehydrogenase initiating the glucose-6-phosphate shunt an alternative pathway around the Calvin-Benson cycle. A low concentration of glucose 6-phosphate will limit this futile cycle. In order to understand the biochemical regulation of plastidic glucose 6-phosphate supply and consumption, we characterized biochemical parameters of two key enzymes, phosphoglucoisomerase (PGI) and G6P dehydrogenase (G6PDH). We have found that the plastidic PGI in has a higher Km for G6P compared to that for fructose 6-phosphate. The Km of G6PDH isoform 1 is increased under reducing conditions. The other two isoforms exhibit less redox regulation; isoform 2 is the most inhibited by NADPH. Our results support the conclusion that PGI restricts stromal G6P synthesis limiting futile cycling via G6PDH. It also acts like a one-way valve, allowing carbon to leave the Calvin-Benson cycle but not reenter. We found flexible redox regulation of G6PDH that could regulate the glucose-6-phosphate shunt.HighlightGlucose 6-phosphate stimulates glucose-6-phosphate dehydrogenase. This enzyme is less active during the day but retains significant activity that is very sensitive to the concentration of glucose 6-phopshate.

scholarly journals Plastidic glucose-6-phosphate dehydrogenases are regulated to maintain activity in the light

2019 ◽  
Vol 476 (10) ◽  
pp. 1539-1551 ◽  
Author(s):  
Alyssa L. Preiser ◽  
Nicholas Fisher ◽  
Aparajita Banerjee ◽  
Thomas D. Sharkey
Keyword(s):  
Recombinant Proteins ◽  
Biochemical Parameters ◽  
Redox Regulation ◽  
Substrate Inhibition ◽  
The Other ◽  
Significant Activity ◽  
Enzyme Kinetic ◽  
Reducing Conditions ◽  
Glucose 6 Phosphate Dehydrogenase

Abstract Glucose-6-phosphate dehydrogenase (G6PDH) can initiate the glucose-6-phosphate (G6P) shunt around the Calvin–Benson cycle. To understand the regulation of flux through this pathway, we have characterized the biochemical parameters and redox regulation of the three functional plastidic isoforms of Arabidopsis G6PDH. When purified, recombinant proteins were measured, all three exhibited significant substrate inhibition by G6P but not NADP+, making the determination of enzyme kinetic parameters complex. We found that the half-saturation concentration of G6PDH isoform 1 is increased under reducing conditions. The other two isoforms exhibit less redox regulation, however, isoform 2 is strongly inhibited by NADPH. Redox regulation of G6PDH1 can be partially reversed by hydrogen peroxide or protected against by the presence of its substrate, G6P. Overall, our results support the conclusion that G6PDH can have significant activity throughout the day and can be dynamically regulated to allow or prevent flux through the glucose-6-phosphate shunt.

Thioredoxin-like2/2-Cys peroxiredoxin redox cascade acts as oxidative activator of glucose-6-phosphate dehydrogenase in chloroplasts

2019 ◽  
Vol 476 (12) ◽  
pp. 1781-1790 ◽  
Author(s):  
Keisuke Yoshida ◽  
Eriko Uchikoshi ◽  
Satoshi Hara ◽  
Toru Hisabori
Keyword(s):  
Redox Regulation ◽  
Pentose Phosphate ◽  
Activation Mechanism ◽  
Protein Activation ◽  
Fluctuating Light ◽  
State Determination ◽  
Chloroplast Metabolism ◽  
Oxidative Activation ◽  
Glucose 6 Phosphate Dehydrogenase ◽  
Novel Protein

Abstract Thiol-based redox regulation is crucial for adjusting chloroplast functions under fluctuating light environments. We recently discovered that the thioredoxin-like2 (TrxL2)/2-Cys peroxiredoxin (2CP) redox cascade supports oxidative thiol modulation by using hydrogen peroxide (H2O2) as an oxidizing force. This system plays a key role in switching chloroplast metabolism (e.g. Calvin–Benson cycle) during light to dark transitions; however, information on its function is still limited. In this study, we report a novel protein-activation mechanism based on the TrxL2/2CP redox cascade. Glucose-6-phosphate dehydrogenase (G6PDH) catalyzes the first step of the oxidative pentose phosphate pathway (OPPP). Biochemical studies, including redox state determination and measurement of enzyme activity, suggested that the TrxL2/2CP pathway is involved in the oxidative activation of G6PDH. It is thus likely that the TrxL2/2CP redox cascade shifts chloroplast metabolism to night mode by playing a dual role, namely, down-regulation of the Calvin–Benson cycle and up-regulation of OPPP. G6PDH was also directly oxidized and activated by H2O2, particularly when H2O2 concentration was elevated. Therefore, G6PDH is thought to be finely tuned by H2O2 levels in both direct and indirect manners.

scholarly journals Is There an Alternative Pathway for Starch Synthesis?

1992 ◽  
Vol 100 (2) ◽  
pp. 560-564 ◽  
Author(s):  
Thomas W. Okita
Keyword(s):  
Alternative Pathway ◽  
Starch Synthesis

Redox regulation of the ryanodine receptor/calcium release channel

2006 ◽  
Vol 34 (5) ◽  
pp. 919-921 ◽  
Author(s):  
S. Zissimopoulos ◽  
F.A. Lai
Keyword(s):  
Ryanodine Receptor ◽  
Protein Interactions ◽  
Redox Regulation ◽  
Opposite Effect ◽  
Calcium Release ◽  
Calcium Release Channel ◽  
Release Channel ◽  
Reducing Conditions ◽  
Channel Opening ◽  
Redox Sensitivity

The RyR (ryanodine receptor)/calcium release channel contains a number of highly reactive thiol groups that endow it with redox sensitivity. In general, oxidizing conditions favour channel opening, while reducing conditions have the opposite effect. Thiol modification affects the channel sensitivity to its principal effectors, Ca2+, Mg2+ and ATP, and alters RyR protein interactions. Here, we give a brief account of the major findings and prevailing views in the field.

scholarly journals Roles for cytosolic NADPH redox in regulating pulmonary artery relaxation by thiol oxidation-elicited subunit dimerization of protein kinase G1α

2013 ◽  
Vol 305 (3) ◽  
pp. H330-H343 ◽  
Author(s):  
Boon Hwa Neo ◽  
Dhara Patel ◽  
Sharath Kandhi ◽  
Michael S. Wolin
Keyword(s):  
Protein Kinase ◽  
Redox Regulation ◽  
Soluble Guanylate Cyclase ◽  
Pulmonary Arteries ◽  
Thiol Oxidation ◽  
Hypoxic Conditions ◽  
Vasp Phosphorylation ◽  
Thioredoxin 1 ◽  
Nadph Oxidation ◽  
Glucose 6 Phosphate Dehydrogenase

The activity of glucose-6-phosphate dehydrogenase (G6PD) appears to control a vascular smooth muscle relaxing mechanism regulated through cytosolic NADPH oxidation. Since our recent studies suggest that thiol oxidation-elicited dimerization of the 1α form of protein kinase G (PKG1α) contributes to the relaxation of isolated endothelium-removed bovine pulmonary arteries (BPA) to peroxide and responses to hypoxia, we investigated whether cytosolic NADPH oxidation promoted relaxation by PKG1α dimerization. Relaxation of BPA to G6PD inhibitors 6-aminonicotinamide (6-AN) and epiandrosterone (studied under hypoxia to minimize basal levels of NADPH oxidation and PKG1α dimerization) was associated with increased PKG1α dimerization and PKG-mediated vasodilator-stimulated phosphoprotein (VASP) phosphorylation. Depletion of PKG1α by small inhibitory RNA (siRNA) inhibited relaxation of BPA to 6-AN and attenuated the increase in VASP phosphorylation. Relaxation to 6-AN did not appear to be altered by depletion of soluble guanylate cyclase (sGC). Depletion of G6PD, thioredoxin-1 (Trx-1), and Trx reductase-1 (TrxR-1) in BPA with siRNA increased PKG1α dimerization and VASP phosphorylation and inhibited force generation under aerobic and hypoxic conditions. Depletion of TrxR-1 with siRNA inhibited the effects of 6-AN and enhanced similar responses to peroxide. Peroxiredoxin-1 depletion by siRNA inhibited PKG dimerization to peroxide, but it did not alter PKG dimerization under hypoxia or the stimulation of dimerization by 6-AN. Thus regulation of cytosolic NADPH redox by G6PD appears to control PKG1α dimerization in BPA through its influence on Trx-1 redox regulation by the NADPH dependence of TrxR-1. NADPH regulation of PKG dimerization may contribute to vascular responses to hypoxia that are associated with changes in NADPH redox.

scholarly journals LOCALIZATION OF NICOTINAMIDE ADENINE DINUCLEOTIDE PHOSPHATE-DEPENDENT DEHYDROGENASES IN CATECHOLAMINE-CONTAINING NEURONS OF RAT BRAIN STUDIES ON THE NUCLEUS LOCUS CERULEUS

1974 ◽  
Vol 22 (1) ◽  
pp. 20-28 ◽  
Author(s):  
F. C. KAUFFMAN ◽  
F. E. BLOOM ◽  
K. L. SIMS ◽  
V. M. PICKEL
Keyword(s):  
Brain Stem ◽  
Rat Brain ◽  
Nicotinamide Adenine Dinucleotide ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Locus Ceruleus ◽  
Nicotinamide Adenine ◽  
High Concentration ◽  
Intense Staining ◽  
Phosphogluconate Dehydrogenase ◽  
Glucose 6 Phosphate Dehydrogenase

Histochemical and cytochemical methods have been used to localize glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, isocitrate (nicotinamide adenine dinucleotide phosphate (NADP)) dehydrogenase and malic enzyme in the nucleus locus ceruleus and other catecholamine-containing neuronal groups of the rat brain stem. The four NADP-dependent dehydrogenases were studied by both quantitative and qualitative histochemical techniques using adjacent tissue sections. Both types of analyses were done on neuronal nuclei known to contain catecholamines in high concentration, the nucleus locus ceruleus and the superior cervical sympathetic ganglion; other known catecholamine-containing nuclei were surveyed by the cytologic technique only. There was intense staining of cell bodies and neuropil of the nucleus locus ceruleus after all four of the NADP dehydrogenase histochemical reactions. In contrast, little staining was observed in the adjacent vestibular nuclei or mesencephalic root nucleus of the trigeminal with the exception of appreciable glucose 6-phosphate dehydrogenase activity present in neuropil elements. Quantitative microchemical determinations in the nucleus locus ceruleus corroborate the histochemical results which indicated high NADP dehydrogenase activities particularly for 6-phosphogluconate dehydrogenase. This same pattern of high NADP enzyme activity as determined by combined cytochemical and quantitative chemical techniques was also observed in the superior cervical ganglion and cytochemically in other catecholamine-containing nuclei of the brain stem. Our findings suggest that a high capacity to generate or utilize nicotinamide adenine dinucleotide phosphate (reduced) may be characteristic of those neurons which either receive adrenergic terminals or synthesize catecholamines.

scholarly journals A mutant phosphofructokinase produces a futile cycle during gluconeogenesis in Escherichia coli

1997 ◽  
Vol 327 (3) ◽  
pp. 675-684 ◽  
Author(s):  
C. Juan TORRES ◽  
Victoria GUIXÉ ◽  
Jorge BABUL
Keyword(s):  
Escherichia Coli ◽  
Carbon Source ◽  
Kinetic Equations ◽  
British Library ◽  
Wild Type ◽  
Futile Cycle ◽  
Co2 Output ◽  
Futile Cycling ◽  
Fructose 1,6 Bisphosphate

Strains of Escherichia coli bearing different forms of phosphofructokinase were used to assess the occurrence of futile cycling in cell resuspensions supplied with glycerol as gluconeogenic carbon source. A model was used to simulate results of different kinds of experiments for different levels of futile cycle. The main predictions of the model were experimentally confirmed in a strain with a mutant phosphofructokinase-2 (phosphofructokinase-2*) which is not inhibited by MgATP. The intracellular fructose 1,6-bisphosphate concentration reaches significantly higher levels in the mutant-bearing strain than in strains with either phosphofructokinase-1 or -2. Also, this strain showed a higher rate and level of in vivo radioactive labelling of fructose 1,6-bisphosphate, from a trace of [U-14C]glucose supplied during gluconeogenesis, indicating higher kinase activity in these conditions. Cell resuspensions of the mutant-bearing strain produced higher levels of radioactively labelled CO2 when supplied with [U-14C]glycerol as the only carbon source. Simultaneously, fewer glycerol carbons were incorporated into HClO4-insoluble macromolecules. Finally, radioactive CO2 output was measured in resuspensions supplied with glycerol as the major carbon source with traces of either [1-14C]glucose or [6-14C]glucose. It was found that, whereas in the strains with either of the wild-type phosphofructokinase isoenzymes, radioactive CO2 output from [1-14C]glucose was higher than with [6-14C]glucose, the reverse is found for the strain with phosphofructokinase-2*. This result also agrees with the corresponding prediction of the model. Using the radioactivity flux rates predicted by the model, an explanation linking the futile cycle to the differential labelling of CO2 is advanced. Finally, on the basis of these results it is proposed that strains bearing phosphofructokinase-2* sustain higher rates of futile cycling during gluconeogenesis than strains bearing either of the wild-type isoforms of phosphofructokinase. The kinetic equations and parameter values used for the model simulations are given in Supplementary Publication SUP 50183 (8 pages), which has been deposited at the British Library Document Supply Centre, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1997) 321, 8.

scholarly journals RNA Futile Cycling in Model Persisters Derived from MazF Accumulation

mBio ◽  
2015 ◽  
Vol 6 (6) ◽  
Author(s):  
Wendy W. K. Mok ◽  
Junyoung O. Park ◽  
Joshua D. Rabinowitz ◽  
Mark P. Brynildsen
Keyword(s):  
Critical Role ◽  
Glucose Consumption ◽  
Rna Degradation ◽  
Futile Cycle ◽  
Bacterial Populations ◽  
Content Type ◽  
Inducible Promoters ◽  
E Coli ◽  
Futile Cycling ◽  
Futile Cycles

ABSTRACTMetabolism plays an important role in the persister phenotype, as evidenced by the number of strategies that perturb metabolism to sabotage this troublesome subpopulation. However, the absence of techniques to isolate high-purity populations of native persisters has precluded direct measurement of persister metabolism. To address this technical challenge, we studiedEscherichia colipopulations whose growth had been inhibited by the accumulation of the MazF toxin, which catalyzes RNA cleavage, as a model system for persistence. Using chromosomally integrated, orthogonally inducible promoters to express MazF and its antitoxin MazE, bacterial populations that were almost entirely tolerant to fluoroquinolone and β-lactam antibiotics were obtained upon MazF accumulation, and these were subjected to direct metabolic measurements. While MazF model persisters were nonreplicative, they maintained substantial oxygen and glucose consumption. Metabolomic analysis revealed accumulation of all four ribonucleotide monophosphates (NMPs). These results are consistent with a MazF-catalyzed RNA futile cycle, where the energy derived from catabolism is dissipated through continuous transcription and MazF-mediated RNA degradation. When transcription was inhibited, oxygen consumption and glucose uptake decreased, and nucleotide triphosphates (NTPs) and NTP/NMP ratios increased. Interestingly, the MazF-inhibited cells were sensitive to aminoglycosides, and this sensitivity was blocked by inhibition of transcription. Thus, in MazF model persisters, futile cycles of RNA synthesis and degradation result in both significant metabolic demands and aminoglycoside sensitivity.IMPORTANCEMetabolism plays a critical role in controlling each stage of bacterial persistence (shutdown, stasis, and reawakening). In this work, we generated anE. colistrain in which the MazE antitoxin and MazF toxin were artificially and independently inducible, and we used this strain to generate model persisters and study their metabolism. We found that even though growth of the model persisters was inhibited, they remained highly metabolically active. We further uncovered a futile cycle driven by continued transcription and MazF-mediated transcript degradation that dissipated the energy derived from carbon catabolism. Interestingly, the existence of this futile cycle acted as an Achilles’ heel for MazF model persisters, rendering them vulnerable to killing by aminoglycosides.

Redox regulation of chloroplastic glucose-6-phosphate dehydrogenase: A new role for f-type thioredoxin

FEBS Letters ◽  
2009 ◽  
Vol 583 (17) ◽  
pp. 2827-2832 ◽  
Author(s):  
Guillaume Née ◽  
Mirko Zaffagnini ◽  
Paolo Trost ◽  
Emmanuelle Issakidis-Bourguet
Keyword(s):  
Redox Regulation ◽  
Glucose 6 Phosphate Dehydrogenase

Chemical Composition and Biological Activity of Propolis from Brazilian Meliponinae

2000 ◽  
Vol 55 (9-10) ◽  
pp. 785-789 ◽  
Author(s):  
Milena Velikova ◽  
Vassya Bankova ◽  
Maria C. Marcucci ◽  
Iva Tsvetkova ◽  
Atanas Kujumgiev
Keyword(s):  
Biological Activity ◽  
Chemical Composition ◽  
Stingless Bees ◽  
Geographical Location ◽  
Artemia Salina ◽  
Cytotoxic Activities ◽  
Significant Activity ◽  
High Concentration ◽  
E Coli ◽  
High Cytotoxic Activity

Abstract Twenty-one propolis samples produced by 12 different Meliponinae species were analyzed by GC-MS. Several chemical types of stingless bees’ propolis could be grouped, according to the prevailing type of compounds like: “gallic acid”, “diterpenic” and “triterpenic” types. The results confirm that neither the bee species nor the geographical location determine the chemical composition of Meliponinae propolis and the choice of its plant source, respectively. This could be explained by the fact that Meliponinae forage over short distances (maximum 500 m) and thus use as propolis source the first plant exudate they encounter during their flights. The antibacterial, antifungal and cytotoxic activities of the samples were also investigated. Most samples had weak or no activity against E. coli, weak action against Candida albicans. Some of them showed significant activity against St. aureus., presumably connected to the high concentration of diterpenic acids. Samples rich in diterpenic acids possessed also high cytotoxic activity (Artemia salina test).

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