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Reducing Equivalents (reducing + equivalent)
Selected AbstractsBioenergetics and the epigenome: Interface between the environment and genes in common diseasesDEVELOPMENTAL DISABILITIES RESEARCH REVIEW, Issue 2 2010Douglas C. Wallace Abstract Extensive efforts have been directed at using genome-wide association studies (GWAS) to identify the genes responsible for common metabolic and degenerative diseases, cancer, and aging, but with limited success. While environmental factors have been evoked to explain this conundrum, the nature of these environmental factors remains unexplained. The availability of and demands for energy constitute one of the most important aspects of the environment. The flow of energy through the cell is primarily mediated by the mitochondrion, which oxidizes reducing equivalents from hydrocarbons via acetyl-CoA, NADH + H+, and FADH2 to generate ATP through oxidative phosphorylation (OXPHOS). The mitochondrial genome encompasses hundreds of nuclear DNA (nDNA)-encoded genes plus 37 mitochondrial DNA (mtDNA)-encoded genes. Although the mtDNA has a high mutation rate, only milder, potentially adaptive mutations are introduced into the population through female oocytes. In contrast, nDNA-encoded bioenergetic genes have a low mutation rate. However, their expression is modulated by histone phosphorylation and acetylation using mitochondrially-generated ATP and acetyl-CoA, which permits increased gene expression, growth, and reproduction when calories are abundant. Phosphorylation, acetylaton, and cellular redox state also regulate most signal transduction pathways and activities of multiple transcription factors. Thus, mtDNA mutations provide heritable and stable adaptation to regional differences while mitochondrially-mediated changes in the epigenome permit reversible modulation of gene expression in response to fluctuations in the energy environment. The most common genomic changes that interface with the environment and cause complex disease must, therefore, be mitochondrial and epigenomic in origin. © 2010 Wiley-Liss, Inc. Dev Disabil Res Rev 2010;16:114,119. [source] The Auxiliary Substrate Concept: From simple considerations to heuristically valuable knowledgeENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 4 2009Wolfgang Babel Abstract Microorganisms are used in biotechnology. They are either (i) aim and purpose of a process, e.g. with the production of single cell proteins, or (ii) mean to an end insofar as they serve as a catalyst or "factory" for syntheses (e.g. of products of primary and secondary metabolism, of enzymes and antibiotics) or for the degradation and detoxification of harmful organics and inorganics. In all cases, the efficiency and velocity, finally the productivity, are parameters which essentially determine the economy of the processes. Therefore, search for approaches to optimize these processes is a permanent task and challenge for scientists and engineers. It is shown that the auxiliary substrate concept is suitable to increase the yield coefficients. It is based on the energetic evaluation of organics, on the knowledge that organics as sources of carbon and energy for growth are deficient in ATP and/or reducing equivalents, and says that it is possible to improve the carbon conversion efficiency up to the carbon metabolism determined upper limit. The latter is determined by inevitable losses of carbon along the way of assimilation and anabolism and amounts to about 85% for so-called glycolytic substrates, e.g. glucose, methanol, and to about 75% for gluconeogenetic substrates, e.g. C2 -substrates (acetic acid, hexadecane). The approach is explained and some experimental examples are presented. By simultaneous utilization of an extra energy source (auxiliary substrate) the yield coefficient can be increased (i) in glucose from about 0.5 to 0.7,g/g (by means of formate), (ii) in acetate from 0.34,0.4 to 0.5,0.65,g/g (by means of formate and thiosulfate, respectively), and (iii) in hexadecane from about 0.94 to 1.26,g/g (by means of formate). The precalculated yield coefficients and mixing ratios agree well with the experimentally attained ones. The approach is easily feasible and economically valuable. [source] Respiratory protection of nitrogenase in Azotobacter species: is a widely held hypothesis unequivocally supported by experimental evidence?FEMS MICROBIOLOGY REVIEWS, Issue 4 2000Jürgen Oelze Abstract The hypothesis of respiratory protection, originally formulated on the basis of results obtained with Azotobacter species, postulates that consumption of O2 at the surface of diazotrophic prokaryotes protects nitrogenase from inactivation by O2. Accordingly, it is assumed that, at increased ambient O2 concentrations, nitrogenase activity depends on increased activities of a largely uncoupled respiratory electron transport system. The present review compiles evidence indicating that cellular O2 consumption as well as both the activity and the formation of the respiratory system of Azotobacter vinelandii are controlled by the C/N ratio, that is to say the ratio at which the organism consumes the substrate (i.e. the source of carbon, reducing equivalents and ATP) per source of compound nitrogen. The maximal respiratory capacity which can be attained at increased C/N ratios, however, is controlled, within limits, by the ambient O2 concentration. When growth becomes N-limited at increased C/N ratios, cells synthesize nitrogenase and fix N2. Under these diazotrophic conditions, cellular O2 consumption remains constant at a level controlled by the O2 concentration. Control by O2 has been studied on the basis of both whole cell respiration and defined segments of the respiratory electron transport chain. The results demonstrate that the effect of O2 on the respiratory system is restricted to the lower range of O2 concentrations up to about 70 ,M. Nevertheless, azotobacters are able to grow diazotrophically at dissolved O2 concentrations of up to about 230 ,M indicating that respiratory protection is not warranted at increased ambient O2 concentrations. This conclusion is supported and extended by a number of results largely excluding an obvious relationship between nitrogenase activity and the actual rate of cellular O2 consumption. On the basis of theoretical calculations, it is assumed that the rate of O2 diffusion into the cells is not significantly affected by respiration. All of these results lead to the conclusion that, in the protection of nitrogenase from O2 damage, O2 consumption at the cell surface is less effective than generally assumed. It is proposed that alternative factors like the supply of ATP and reducing equivalents are more important. [source] The potential significance of microbial Fe(III) reduction during deposition of Precambrian banded iron formationsGEOBIOLOGY, Issue 3 2005K. O. KONHAUSER ABSTRACT During deposition of late Archean,early Palaeoproterozoic Precambrian banded iron formations (BIFs) the downward flux of ferric hydroxide (Fe(OH)3) and phytoplankton biomass should have facilitated microbial Fe(III) reduction. However, quantifying the significance of such a metabolic pathway in the Precambrian is extremely difficult, considering the post-depositional alteration of the rocks and the lack of ideal modern analogues. Consequently, we have very few constraints on the Fe cycle at that time, namely (i) the concentration of dissolved Fe(II) in the ocean waters; (ii) by what mechanisms Fe(II) was oxidized (chemical, photochemical or biological, the latter using either O2 or light); (iii) where the ferric hydroxide was precipitated (over the shelf vs. open ocean); (iv) the amount of phytoplankton biomass, which relates to the nutrient status of the surface waters; (v) the relative importance of Fe(III) reduction vs. the other types of metabolic pathways utilized by sea floor microbial communities; and (vi) the proportion of primary vs. diagenetic Fe(II) in BIF. Furthermore, although estimates can be made regarding the quantity of reducing equivalents necessary to account for the diagenetic Fe(II) component in Fe-rich BIF layers, those same estimates do not offer any insights into the magnitude of Fe(III) actually generated within the water column, and hence, the efficiency of Fe and C recycling prior to burial. Accordingly, in this study, we have attempted to model the ancient Fe cycle, based simply on conservative experimental rates of photosynthetic Fe(II) oxidation in the euphotic zone. We estimate here that under ideal growth conditions, as much as 70% of the biologically formed Fe(III) could have been recycled back into the water column via fermentation and organic carbon oxidation coupled to microbial Fe(III) reduction. By comparing the potential amount of biomass generated phototrophically with the reducing equivalents required for Fe(III) reduction and magnetite formation, we also hypothesize that another anaerobic metabolic pathway might have been utilized in the surface sediment to oxidize the fermentation by-products. Based on the premise that the deep ocean waters were anoxic, this role could have been fulfilled by methanogens, and maybe even methanotrophs that employed Fe(III) reduction. [source] Ethanol synthesis from glycerol by Escherichia coli redox mutants expressing adhE from Leuconostoc mesenteroidesJOURNAL OF APPLIED MICROBIOLOGY, Issue 2 2010P.I. Nikel Abstract Aims:, Analysis of the physiology and metabolism of Escherichia coli arcA and creC mutants expressing a bifunctional alcohol-acetaldehyde dehydrogenase from Leuconostoc mesenteroides growing on glycerol under oxygen-restricted conditions. The effect of an ldhA mutation and different growth medium modifications was also assessed. Methods and Results:, Expression of adhE in E. coli CT1061 [arcA creC(Con)] resulted in a 1·4-fold enhancement in ethanol synthesis. Significant amounts of lactate were produced during micro-oxic cultures and strain CT1061LE, in which fermentative lactate dehydrogenase was deleted, produced up to 6·5 ± 0·3 g l,1 ethanol in 48 h. Escherichia coli CT1061LE derivatives resistant to >25 g l,1 ethanol were obtained by metabolic evolution. Pyruvate and acetaldehyde addition significantly increased both biomass and ethanol concentrations, probably by overcoming acetyl-coenzyme A (CoA) shortage. Yeast extract also promoted growth and ethanol synthesis, and this positive effect was mainly attributable to its vitamin content. Two-stage bioreactor cultures were conducted in a minimal medium containing 100 ,g l,1 calcium d -pantothenate to evaluate oxic acetyl-CoA synthesis followed by a switch into fermentative conditions. Ethanol reached 15·4 ± 0·9 g l,1 with a volumetric productivity of 0·34 ± 0·02 g l,1 h,1. Conclusions:,Escherichia coli responded to adhE over-expression by funnelling carbon and reducing equivalents into a highly reduced metabolite, ethanol. Acetyl-CoA played a key role in micro-oxic ethanol synthesis and growth. Significance and Impact of the Study:, Insight into the micro-oxic metabolism of E. coli growing on glycerol is essential for the development of efficient industrial processes for reduced biochemicals production from this substrate, with special relevance to biofuels synthesis. [source] Energy sources for glutamate neurotransmission in the retina: absence of the aspartate/glutamate carrier produces reliance on glycolysis in gliaJOURNAL OF NEUROCHEMISTRY, Issue 1 2007Y. Xu Abstract The mitochondrial transporter, the aspartate/glutamate carrier (AGC), is a necessary component of the malate/aspartate cycle, which promotes the transfer into mitochondria of reducing equivalents generated in the cytosol during glycolysis. Without transfer of cytosolic reducing equivalents into mitochondria, neither glucose nor lactate can be completely oxidized. In the present study, immunohistochemistry was used to demonstrate the absence of AGC from retinal glia (Müller cells), but its presence in neurons and photoreceptor cells. To determine the influence of the absence of AGC on sources of ATP for glutamate neurotransmission, neurotransmission was estimated in both light- and dark-adapted retinas by measuring flux through the glutamate/glutamine cycle and the effect of light on ATP-generating reactions. Neurotransmission was 80% faster in the dark as expected, because photoreceptors become depolarized in the dark and this depolarization induces release of excitatory glutamate neurotransmitter. Oxidation of [U- 14C]glucose, [1- 14C]lactate, and [1- 14C]pyruvate in light- and dark-adapted excised retinas was estimated by collecting 14CO2. Neither glucose nor lactate oxidation that require participation of the malate/aspartate shuttle increased in the dark, but pyruvate oxidation that does not require the malate/aspartate shuttle increased to 36% in the dark. Aerobic glycolysis was estimated by measuring the rate of lactate appearance. Glycolysis was 37% faster in the dark. It appears that in the retina, ATP consumed during glutamatergic neurotransmission is replenished by ATP generated glycolytically within the retinal Müller cells and that oxidation of glucose within the Müller cells does not occur or occurs only slowly. [source] Importance of AOX pathway in optimizing photosynthesis under high light stress: role of pyruvate and malate in activating AOXPHYSIOLOGIA PLANTARUM, Issue 1 2010Challabathula Dinakar The present study shows the importance of alternative oxidase (AOX) pathway in optimizing photosynthesis under high light (HL). The responses of photosynthesis and respiration were monitored as O2 evolution and O2 uptake in mesophyll protoplasts of pea pre-incubated under different light intensities. Under HL (3000 µmol m,2 s,1), mesophyll protoplasts showed remarkable decrease in the rates of NaHCO3 -dependent O2 evolution (indicator of photosynthetic carbon assimilation), while decrease in the rates of respiratory O2 uptake were marginal. While the capacity of AOX pathway increased significantly by two fold under HL, the capacity of cytochrome oxidase (COX) pathway decreased by >50% compared with capacities under darkness and normal light (NL). Further, the total cellular levels of pyruvate and malate, which are assimilatory products of active photosynthesis and stimulators of AOX activity, were increased remarkably parallel to the increase in AOX protein under HL. Upon restriction of AOX pathway using salicylhydroxamic acid (SHAM), the observed decrease in NaHCO3 -dependent O2 evolution or p -benzoquinone (BQ)-dependent O2 evolution [indicator of photosystem II (PSII) activity] and the increase in total cellular levels of pyruvate and malate were further aggravated/promoted under HL. The significance of raised malate and pyruvate levels in activation of AOX protein/AOX pathway, which in turn play an important role in dissipating excess chloroplastic reducing equivalents and sustenance of photosynthetic carbon assimilation to balance the effects of HL stress on photosynthesis, was depicted as a model. [source] Environmental and hormonal regulation of the activity,dormancy cycle in the cambial meristem involves stage-specific modulation of transcriptional and metabolic networksTHE PLANT JOURNAL, Issue 4 2007Nathalie Druart Summary We have performed transcript and metabolite profiling of isolated cambial meristem cells of the model tree aspen during the course of their activity,dormancy cycle to better understand the environmental and hormonal regulation of this process in perennial plants. Considerable modulation of cambial transcriptome and metabolome occurs throughout the activity,dormancy cycle. However, in addition to transcription, post-transcriptional control is also an important regulatory mechanism as exemplified by the regulation of cell-cycle genes during the reactivation of cambial cell division in the spring. Genes related to cold hardiness display temporally distinct induction patterns in the autumn which could explain the step-wise development of cold hardiness. Factors other than low temperature regulate the induction of early cold hardiness-related genes whereas abscisic acid (ABA) could potentially regulate the induction of late cold hardiness-related genes in the autumn. Starch breakdown in the autumn appears to be regulated by the ,short day' signal and plays a key role in providing substrates for the production of energy, fatty acids and cryoprotectants. Catabolism of sucrose and fats provides energy during the early stages of reactivation in the spring, whereas the reducing equivalents are generated through activation of the pentose phosphate shunt. Modulation of gibberellin (GA) signaling and biosynthesis could play a key role in the regulation of cambial activity during the activity,dormancy cycle as suggested by the induction of PttRGA which encodes a negative regulator of growth in the autumn and that of a GA-20 oxidase, a key gibberellin biosynthesis gene during reactivation in spring. In summary, our data reveal the dynamics of transcriptional and metabolic networks and identify potential targets of environmental and hormonal signals in the regulation of the activity,dormancy cycle in cambial meristem. [source] Effect of high environmental temperatures on ascorbic acid, sulfhydryl residue and oxidized lipid concentrations in plasma of dairy cowsANIMAL SCIENCE JOURNAL, Issue 3 2007Masahito TANAKA ABSTRACT Information on oxidative stress under hot conditions from the levels of cells to organs and the whole body has accumulated in the last decades. Although a hot climate decreased dairy performance, changes of oxidative stress markers under hot conditions have remained obscure. Therefore, the effect of high environmental temperature on ascorbic acid, sulfhydryl (SH) residue and oxidized lipids concentrations in plasma from a total of 128 dairy cows was investigated. The monthly average maximum day temperature varied from 9.2°C in January to 32°C in August of 2004 in this institute. High ambient temperatures increased the rectal temperature of dairy cows up to 39.3°C in August. One of the reducing equivalents in plasma, SH residue concentration, decreased in July compared with December (P < 0.05). Another antiradical molecule, ascorbic acid concentration in plasma, also decreased in July (P < 0.01). The oxidative stress index, thiobarbituric acid reactive substance (TBARS), which was produced from the oxidation of polyunsaturated fatty acids under oxidative conditions, increased in summer (P < 0.05). A significant positive relationship of SH residue and ascorbic acid concentrations in the hot season was observed (P < 0.01). A negative correlation between rectal temperatures and ascorbic acid concentrations in the hot season was obtained (P < 0.01). However, TBARS concentration varied independently of the SH residue and ascorbic acid concentration. These results suggest that the response of oxidative stress markers of SH residue, ascorbic acid and TBARS concentration to oxidative stress under hot conditions were not shown to be the same, and that oxidative stress in dairy cows in the hot season increased. [source] Structure of Hordeum vulgare NADPH-dependent thioredoxin reductase 2.ACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2009Unwinding the reaction mechanism Thioredoxins (Trxs) are protein disulfide reductases that regulate the intracellular redox environment and are important for seed germination in plants. Trxs are in turn regulated by NADPH-dependent thioredoxin reductases (NTRs), which provide reducing equivalents to Trx using NADPH to recycle Trxs to the active form. Here, the first crystal structure of a cereal NTR, HvNTR2 from Hordeum vulgare (barley), is presented, which is also the first structure of a monocot plant NTR. The structure was determined at 2.6,Å resolution and refined to an Rcryst of 19.0% and an Rfree of 23.8%. The dimeric protein is structurally similar to the structures of AtNTR-B from Arabidopsis thaliana and other known low-molecular-weight NTRs. However, the relative position of the two NTR cofactor-binding domains, the FAD and the NADPH domains, is not the same. The NADPH domain is rotated by 25° and bent by a 38% closure relative to the FAD domain in comparison with AtNTR-B. The structure may represent an intermediate between the two conformations described previously: the flavin-oxidizing (FO) and the flavin-reducing (FR) conformations. Here, analysis of interdomain contacts as well as phylogenetic studies lead to the proposal of a new reaction scheme in which NTR,Trx interactions mediate the FO to FR transformation. [source] Transplasma membrane electron transport comes in two flavorsBIOFACTORS, Issue 3 2008Darius J. R. Lane Abstract All tested cells possess transplasma membrane electron transfer (tPMET) systems that are capable of reducing extracellular electron acceptors at the cost of cytosolic electron donors. In mammals, classically NAD(P)H- and NADH-dependent systems have been distinguished. The NADH-dependent system has been suggested to be involved in non-transferrin-bound iron (NTBI) reduction and uptake. Recently we reported that transplasma membrane ascorbate/dehydroascorbate cycling can promote NTBI reduction and uptake by human erythroleukemia (K562) cells (D.J.R. Lane and A. Lawen, J Biol Chem 283 (2008), 12701-12708). This system, involves i) cellular import of dehydroascorbate, ii) intracellular reduction of dehydroascorbate to ascorbate using metabolically-derived reducing equivalents, iii) export of ascorbate down its concentration gradient, iv) direct reduction of low molecular weight iron chelates by ascorbate, and v) uptake of iron (II) into the cell. We here propose the consideration of this system as a novel form of tPMET which shares with classical enzyme-mediated tPMET systems the net transfer of reducing equivalents from the cytoplasmic compartment to the extracellular space, but lacks the involvement of the plasma membrane oxidoreductases responsible for the latter. Thus, transplasma membrane electron transfer can and does occur at two mechanistically distinct levels: i) enzyme-mediated transmembrane electron transfer and ii) transmembrane metabolite shuttling/cycling. [source] Effect of Overexpression of a Soluble Pyridine Nucleotide Transhydrogenase (UdhA) on the Production of Poly(3-hydroxybutyrate) in Escherichia coliBIOTECHNOLOGY PROGRESS, Issue 2 2006Ailen M. Sánchez A soluble pyridine nucleotide transhydrogenase (UdhA) has been used to increase the productivity and yield of PHB in vivo. By inducing a high level of UdhA, which can transfer reducing equivalents between NAD and NADP, we have increased NADPH availability, resulting in high yield and productivity of PHB in Escherichia coli. Coexpression of the phboperon from Alcaligenes eutrophusH16 and the native udhAfrom E. coli from high copy plasmids resulted in an increase in PHB yield from 49 to 66% g of PHB per gram of total cell dry weight and an increase in final concentration from 3.52 to 6.42 g/L; the PHB concentration of the udhA carrying strain is almost twice that of the control strain expressing only the phb operon. The results of this study demonstrate the effectiveness of cofactor manipulation and its application as a tool in metabolic engineering. [source] | |||||||||||||||||||