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1
Liu, Xiao Chen, Ping Wang, Ying Long He, Yong Lei Kou, Biao Zhang, Gui Fu Dai e Jian Wu. "Rapid Determination of Pentose and Hexose Sugars in Mixed Sugars by Multiple Linear Regression Calibration Method". Applied Mechanics and Materials 145 (dicembre 2011): 159–63. http://dx.doi.org/10.4028/www.scientific.net/amm.145.159.
Testo completoAbstract (sommario):
This research provides an improvement for the method of Douglas to determine pentose and hexose sugars in mixed sugars. Specific absorption wave of 553 nm for pentose derivatives and 408 nm for hexose derivatives are selected for determination, and the interference from pentose sugar to hexose sugar is corrected with multiple linear regression method. The results show that the interference from pentose sugar is reduced greatly after multiple linear regression calibration; the error is lower than 5.0 %. The experimental results show a satisfying precision and accuracy, with a recovery range from 95.1 % to 106.8%. This method is suitable for simultaneously rapid determination of pentose and hexose sugars in practical application.
2
Balibrea, María E., Cristina Martínez-Andújar, Jesús Cuartero, María C. Bolarín e Francisco Pérez-Alfocea. "The high fruit soluble sugar content in wild Lycopersicon species and their hybrids with cultivars depends on sucrose import during ripening rather than on sucrose metabolism". Functional Plant Biology 33, n. 3 (2006): 279. http://dx.doi.org/10.1071/fp05134.
Testo completoAbstract (sommario):
Soluble sugar content has been studied in relation to sucrose metabolism in the hexose-accumulating cultivated tomato Lycopersicon esculentum Mill, the wild relative species Lycopersicon cheesmanii Riley, in the sucrose-accumulating wild relative species Lycopersicon chmielewskii Rick, Kesicky, Fobes & Holle. and in two hexose-accumulating interspecific F1 hybrids (L. esculentum × L. cheesmanii; L. esculentum × L. chmielewskii), cultivated under two irrigation regimes (control: EC = 2.1 and saline: EC = 8.4 dS m–1). Under control conditions the total soluble sugar content (as hexose equivalents) in the ripe fruits of L. cheesmanii was 3-fold higher than in L. esculentum, while L. chmielewskii and both F1 hybrids contained twice as much as the cultivar. With the exception of L. esculentum × L. cheesmanii, salinity increased the sugar content by 1.3 (wild species) and 1.7 times (cultivar and L. esculentum × L. chmielewskii) with respect to control fruits. Wild germplasm or salinity provided two different mechanisms for the increases in fruit sugar content. The hexoses accumulated in ripe fruits were strongly influenced by those accumulated at the start of ripening, but the hydrolysed starch before start of ripening only partially explained the final hexose levels and especially the increase under salinity. The early cell wall acid invertase and the late neutral invertase activities appeared to be related to the amount of hexoses accumulated in ripe fruits. However, no metabolic parameter was positively related to the amount of sugar accumulated (including sucrose). The major differences between genotypes appeared in ripe fruits, in which up to 50% of the total amount of sugars accumulated in the wild species (mainly in L. cheesmanii) and hybrids cannot be explained by the sugars accumulated and the starch hydrolysed before the start of ripening stage. As a consequence, the higher fruit quality of the wild species compared with L. esculentum may depend more on the continuation of sucrose import during ripening than on osmotic or metabolic particularities such as the hexose / sucrose-accumulator character or specific enzyme activities.
3
Granot, David. "Role of tomato hexose kinases". Functional Plant Biology 34, n. 6 (2007): 564. http://dx.doi.org/10.1071/fp06207.
Testo completoAbstract (sommario):
Hexose phosphorylation is an essential step of sugar metabolism. Only two classes of glucose and fructose phosphorylating enzymes, hexokinases (HXK) and fructokinases (FRK), have been found in plants. Tomato (Lycopersicon esculentum Mill.) is the only plant species from which four HXK and four FRK genes have been identified and characterised. One HXK and one FRK isozyme are located within plastids. The other three HXK isozymes are associated with the mitochondria, and the other three FRK isozymes are dispersed in the cytosol. These differences in location suggest that the cytoplasmic HXK and FRK have distinct roles to play in sugar metabolism. The specific roles of each of the HXK and FRK genes have been investigated using transgenic plants with modified expression of the genes. Sugar signalling effects were obtained with modified expression of the mitochondria associated HXK. In contrast, modified expression of the cytosolic FRK affected fructose metabolism rather than sugar signalling. Future research efforts will aim to determining the roles of specific hexose phosphorylating enzymes in tomato plants, the source of the hexose monomers to be phosphorylated, and their intracellular trafficking route.
4
Siu, Sarah, Anna Robotham, Susan M. Logan, John F. Kelly, Kaoru Uchida, Shin-Ichi Aizawa e Ken F. Jarrell. "Evidence that Biosynthesis of the Second and Third Sugars of the Archaellin Tetrasaccharide in the Archaeon Methanococcus maripaludis Occurs by the Same Pathway Used by Pseudomonas aeruginosa To Make a Di-N-Acetylated Sugar". Journal of Bacteriology 197, n. 9 (2 marzo 2015): 1668–80. http://dx.doi.org/10.1128/jb.00040-15.
Testo completoAbstract (sommario):
ABSTRACTMethanococcus maripaludishas two surface appendages, archaella and type IV pili, which are composed of glycoprotein subunits. Archaellins are modified with an N-linked tetrasaccharide with the structure Sug-1,4-β-ManNAc3NAmA6Thr-1,4-β-GlcNAc3NAcA-1,3-β-GalNAc, where Sug is (5S)-2-acetamido-2,4-dideoxy-5-O-methyl-α-l-erythro-hexos-5-ulo-1,5-pyranose. The pilin glycan has an additional hexose attached to GalNAc. In this study, genes located in two adjacent, divergently transcribed operons (mmp0350-mmp0354andmmp0359-mmp0355) were targeted for study based on annotations suggesting their involvement in biosynthesis of N-glycan sugars. Mutants carrying deletions inmmp0350,mmp0351,mmp0352, ormmp0353were nonarchaellated and synthesized archaellins modified with a 1-sugar glycan, as estimated from Western blots. Mass spectroscopy analysis of pili purified from the Δmmp0352strain confirmed a glycan with only GalNAc, suggestingmmp0350tommp0353were all involved in biosynthesis of the second sugar (GlcNAc3NAcA). The Δmmp0357mutant was archaellated and had archaellins with a 2-sugar glycan, as confirmed by mass spectroscopy of purified archaella, indicating a role for MMP0357 in biosynthesis of the third sugar (ManNAc3NAmA6Thr).M. maripaludismmp0350,mmp0351,mmp0352,mmp0353, andmmp0357are proposed to be functionally equivalent toPseudomonas aeruginosawbpABEDI, involved in converting UDP-N-acetylglucosamine to UDP-2,3-diacetamido-2,3-dideoxy-d-mannuronic acid, an O5-specific antigen sugar. Cross-domain complementation of the final step of theP. aeruginosapathway withmmp0357supports this hypothesis.IMPORTANCEThis work identifies a series of genes in adjacent operons that are shown to encode the enzymes that complete the entire pathway for generation of the second and third sugars of the N-linked tetrasaccharide that modifies archaellins ofMethanococcus maripaludis. This posttranslational modification of archaellins is important, as it is necessary for archaellum assembly. Pilins are modified with a different N-glycan consisting of the archaellin tetrasaccharide but with an additional hexose attached to the linking sugar. Mass spectrometry analysis of the pili of one mutant strain provided insight into how this different glycan might ultimately be assembled. This study includes a rare example of an archaeal gene functionally replacing a bacterial gene in a complex sugar biosynthesis pathway.
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Lothier, Jérémy, Bertrand Lasseur, Marie-Pascale Prud'homme e Annette Morvan-Bertrand. "Hexokinase-dependent sugar signaling represses fructan exohydrolase activity in Lolium perenne". Functional Plant Biology 37, n. 12 (2010): 1151. http://dx.doi.org/10.1071/fp10086.
Testo completoAbstract (sommario):
Defoliation of perennial ryegrass (Lolium perenne L.) by grazing animals leads to fructan mobilisation via an increase of fructan exohydrolase (FEH) activity. To highlight the regulation of fructan metabolism in perennial ryegrass, the role of sugars as signalling molecules for regulation of FEH activity after defoliation was evaluated. We used an original approach in planta by spraying stubble of defoliated plants (sugar starved plants) during 24 h with metabolisable sugars (glucose, fructose, sucrose) and sugar analogues (3-O-methylglucose, mannose, lactulose, turanose, palatinose). Metabolisable sugar (glucose, fructose, sucrose) supply following defoliation led to the repression of FEH activity increase. The supply of mannose, which is phosphorylated by hexokinase but not further metabolisable, led to the same repressive effect, whereas 3-O-methylglucose, which is not a substrate for hexokinase, had no effect. These results indicate that hexoses could be sensed by hexokinase, triggering a chain of events leading to the repression of FEH activity. By contrast, it was not possible to determine the role of sucrose as a signal since the supply of sucrose analogues (lactulose, turanose and palatinose) enhanced internal hexose content.
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Li, Yaxin, Huan Liu, Xuehui Yao, Jiang Wang, Sheng Feng, Lulu Sun, Si Ma, Kang Xu, Li-Qing Chen e Xiaolei Sui. "Hexose transporter CsSWEET7a in cucumber mediates phloem unloading in companion cells for fruit development". Plant Physiology 186, n. 1 (5 febbraio 2021): 640–54. http://dx.doi.org/10.1093/plphys/kiab046.
Testo completoAbstract (sommario):
Abstract In the fleshy fruit of cucumbers (Cucumis sativus L.), the phloem flow is unloaded via an apoplasmic pathway, which requires protein carriers to export sugars derived from stachyose and raffinose into the apoplasm. However, transporter(s) involved in this process remain unidentified. Here, we report that a hexose transporter, CsSWEET7a (Sugar Will Eventually be Exported Transporter 7a), was highly expressed in cucumber sink tissues and localized to the plasma membrane in companion cells of the phloem. Its expression level increased gradually during fruit development. Down-regulation of CsSWEET7a by RNA interference (RNAi) resulted in smaller fruit size along with reduced soluble sugar levels and reduced allocation of 14C-labelled carbon to sink tissues. CsSWEET7a overexpression lines showed an opposite phenotype. Interestingly, genes encoding alkaline α-galactosidase (AGA) and sucrose synthase (SUS) were also differentially regulated in CsSWEET7a transgenic lines. Immunohistochemical analysis demonstrated that CsAGA2 co-localized with CsSWEET7a in companion cells, indicating cooperation between AGA and CsSWEET7a in fruit phloem unloading. Our findings indicated that CsSWEET7a is involved in sugar phloem unloading in cucumber fruit by removing hexoses from companion cells to the apoplasmic space to stimulate the raffinose family of oligosaccharides (RFOs) metabolism so that additional sugars can be unloaded to promote fruit growth. This study also provides a possible avenue towards improving fruit production in cucumber.
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Schmidt, Stefan, Hans-Georg Joost e Annette Schürmann. "GLUT8, the enigmatic intracellular hexose transporter". American Journal of Physiology-Endocrinology and Metabolism 296, n. 4 (aprile 2009): E614—E618. http://dx.doi.org/10.1152/ajpendo.91019.2008.
Testo completoAbstract (sommario):
GLUT8 is a class III sugar transporter predominantly expressed in testis and brain. In contrast to the class I and class II transporters, hydrophobicity plots predict a short extracellular loop between transmembrane domain (TM)1 and TM2 and a long extracellular loop between TM9 and TM10 that contains the only N-glycosylation site. In vitro translated GLUT8 migrates as a 35-kDa protein that is glycosylated in the presence of microsomal membranes. In heterologous expression systems, glucose transport activity ( Km of 2 mM) was inhibited by fructose and galactose. The transporter carries an NH2-terminal endosomal/lysosomal targeting motif ([DE]XXXL[LI]). Accordingly, constitutive GLUT8 has been found to be associated with endosomes and lysosomes but also with membranes of the endoplasmic reticulum. A similar distribution was detected after overexpression of wild-type or tagged GLUT8 in different cell systems. In these cells, none of the conventional signals tested induced a translocation of GLUT8 to the plasma membrane. Therefore, GLUT8 appears to catalyze transport of sugars or sugar derivatives through intracellular membranes. Slc2a8 knockout mice were viable, developed normally, and showed mild alterations in brain (increased proliferation of neuronal cells in dentate gyrus of the hippocampus, hyperactivity), heart (impaired transmission of electrical wave through the atrium), and sperm cells (reduced number of motile sperm cells associated with reduced mitochondrial membrane potential and ATP levels in sperm). The links between molecular function, cellular localization and phenotype of the knockout mouse is unclear and remains to be determined.
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Dai, Zhan Wu, Philippe Vivin, Thierry Robert, Sylvie Milin, Shao Hua Li e Michel Génard. "Model-based analysis of sugar accumulation in response to source - sink ratio and water supply in grape (Vitis vinifera) berries". Functional Plant Biology 36, n. 6 (2009): 527. http://dx.doi.org/10.1071/fp08284.
Testo completoAbstract (sommario):
The dynamics of sugar (hexose) concentration in ripening grape berries (Vitis vinifera L.) were simulated with a refined mechanistic model. Changes in sugar concentration were reproduced by the sum of sugar import (S), sugar metabolism (M) and water budget (W). S and W were derived from model inputs of fresh and dry mass, and M was simulated with a relative metabolism rate describing the depletion of hexose. The relative metabolism rate was associated with the relative growth rate of dry mass with a coefficient (k) that was constant for a given cultivar under various growth conditions (temperature, water supply, and source–sink ratio) but varied with genotype. The k value was ~20% higher for cv. Merlot than for cv. Cabernet Sauvignon, indicating more imported sugars would be depleted by Merlot than Cabernet Sauvignon. The model correctly simulated the negative effect of lowered leaf-to-fruit ratio and the positive effect of water shortage on sugar concentration. Sensitivity analysis revealed that the present model was weakly sensitive to k because of sugar accumulation being predominantly controlled by S, with M relatively small (~20%) with respect to the increment of sugar concentration. Model simulation indicated that the decreasing leaf-to-fruit ratio reduced S more than M and W, causing a net decrease in sugar concentration. In contrast, the water shortage decreased S less than M and W, resulting in a net increase in sugar concentration.
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Downs, Colleen T. "Sugar Preference and Apparent Sugar Assimilation in the Red Lory". Australian Journal of Zoology 45, n. 6 (1997): 613. http://dx.doi.org/10.1071/zo97034.
Testo completoAbstract (sommario):
The red lory, Eos bornea (family Psittacidae), was tested to determine its preference for hexose sugars or sucrose. The indices of sugar preference used were (a) number of visits to feeders, (b) time spent feeding and (c) volume of solution drunk. The red lory showed no preference for a specific sugar when offered a choice of glucose, fructose and sucrose at a concentration of 0.73 mol L-1. However, when concentration of the sugars was 0.25 mol L-1, the red lory showed no significant preference by the number of visits but it showed a preference for sucrose by increasing the time spent feeding and the volume drunk. The choice made at lower concentrations may reflect preference for the sugar with the highest energy reward. Birds were fed 0.25 mol L-1 sucrose, 0.73 mol L-1 sucrose and 0.73 mol L-1 glucose in separate laboratory trials to determine the concentration of sugar in the excreta. The red lory was efficient at energy extraction, excreting less than 1% sucrose equivalent, irrespective of the initial sugar concentration of each diet.
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Díaz-Fernández, David, Gloria Muñoz-Fernández, Victoria Isabel Martín, José Luis Revuelta e Alberto Jiménez. "Sugar transport for enhanced xylose utilization in Ashbya gossypii". Journal of Industrial Microbiology & Biotechnology 47, n. 12 (9 ottobre 2020): 1173–79. http://dx.doi.org/10.1007/s10295-020-02320-5.
Testo completoAbstract (sommario):
AbstractThe co-utilization of mixed (pentose/hexose) sugars constitutes a challenge for microbial fermentations. The fungus Ashbya gossypii, which is currently exploited for the industrial production of riboflavin, has been presented as an efficient biocatalyst for the production of biolipids using xylose-rich substrates. However, the utilization of xylose in A. gossypii is hindered by hexose sugars. Three A. gossypii homologs (AFL204C, AFL205C and AFL207C) of the yeast HXT genes that code for hexose transporters have been identified and characterized by gene-targeting approaches. Significant differences in the expression profile of the HXT homologs were found in response to different concentrations of sugars. More importantly, an amino acid replacement (N355V) in AFL205Cp, introduced by CRISPR/Cas9-mediated genomic edition, notably enhanced the utilization of xylose in the presence of glucose. Hence, the introduction of the afl205c-N355V allele in engineered strains of A. gossypii will further benefit the utilization of mixed sugars in this fungus.
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Park, Sang-Hyun, Bok-Rye Lee, Van Hien La, Md Al Mamun, Dong-Won Bae e Tae-Hwan Kim. "Drought Intensity-Responsive Salicylic Acid and Abscisic Acid Crosstalk with the Sugar Signaling and Metabolic Pathway in Brassica napus". Plants 10, n. 3 (23 marzo 2021): 610. http://dx.doi.org/10.3390/plants10030610.
Testo completoAbstract (sommario):
The aim of this study was to characterize hormonal crosstalk with the sugar signaling and metabolic pathway based on a time course analysis of drought intensity. Drought intensity-responsive changes in the assimilation of newly fixed carbon (C) into soluble sugar, the content of sugar and starch, and expression of genes involved in carbohydrate metabolism were interpreted as being linked to endogenous abscisic acid (ABA) and salicylic acid (SA) levels and their signaling genes. The ABA and SA levels in the drought-stressed leaves increased together during the early drought period (days 0–6), and additional ABA accumulation occurred with depressed SA during the late period (days 6–14). Although drought treatment decreased the assimilation of newly fixed C into soluble sugar, representing a 59.9%, 33.1%, and 62.9% reduction in 13C-glucose, 13C-fructose, and 13C-sucrose on day 14, respectively, the drought-responsive accumulation of soluble sugars was significant. During the early period, the drought-responsive accumulation of hexose and sucrose was concurrent with the upregulated expression of hexokinase 1 (HXK1), which, in turn, occurred parallel to the upregulation of ABA synthesis gene 9-sis-epoxycarotenoid dioxygenase (NCED3) and SA-related genes (isochorismate synthase 1 (ICS1) and non-expressor of pathogenesis-related gene (NPR1)). During the late period, hexose accumulation, sucrose phloem loading, and starch degradation were dominant, with a highly enhanced expression of the starch degradation-related genes β-amylase 1 (BAM1) and α-amylase 3 (AMY3), which were concomitant with the parallel enhancement of sucrose non-fermenting−1 (Snf1)-related protein kinase 2 (SnRK2).2 and ABA-responsive element binding 2 (AREB2) expression in an ABA-dependent manner. These results indicate that the drought-responsive accumulation of sugars (especially SA-mediated sucrose accumulation) is part of the acclamatory process during the early period. Conversely, ABA-responsive hexose accumulation and sucrose phloem loading represent severe drought symptoms during the late drought period.
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Brown, Victoria, Jessica A. Sexton e Mark Johnston. "A Glucose Sensor in Candida albicans". Eukaryotic Cell 5, n. 10 (ottobre 2006): 1726–37. http://dx.doi.org/10.1128/ec.00186-06.
Testo completoAbstract (sommario):
ABSTRACT The Hgt4 protein of Candida albicans (orf19.5962) is orthologous to the Snf3 and Rgt2 glucose sensors of Saccharomyces cerevisiae that govern sugar acquisition by regulating the expression of genes encoding hexose transporters. We found that HGT4 is required for glucose induction of the expression of HGT12, HXT10, and HGT7, which encode apparent hexose transporters in C. albicans. An hgt4Δ mutant is defective for growth on fermentable sugars, which is consistent with the idea that Hgt4 is a sensor of glucose and similar sugars. Hgt4 appears to be sensitive to glucose levels similar to those in human serum (∼5 mM). HGT4 expression is repressed by high levels of glucose, which is consistent with the idea that it encodes a high-affinity sugar sensor. Glucose sensing through Hgt4 affects the yeast-to-hyphal morphological switch of C. albicans cells: hgt4Δ mutants are hypofilamented, and a constitutively signaling form of Hgt4 confers hyperfilamentation of cells. The hgt4Δ mutant is less virulent than wild-type cells in a mouse model of disseminated candidiasis. These results suggest that Hgt4 is a high-affinity glucose sensor that contributes to the virulence of C. albicans.
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Zhang, Zhan, Luming Zou, Chong Ren, Fengrui Ren, Yi Wang, Peige Fan, Shaohua Li e Zhenchang Liang. "VvSWEET10 Mediates Sugar Accumulation in Grapes". Genes 10, n. 4 (28 marzo 2019): 255. http://dx.doi.org/10.3390/genes10040255.
Testo completoAbstract (sommario):
Sugar accumulation is a critical event during grape berry ripening that determines the grape market values. Berry cells are highly dependent on sugar transporters to mediate cross-membrane transport. However, the role of sugar transporters in improving sugar accumulation in berries is not well established in grapes. Herein we report that a Sugars Will Eventually be Exported Transporter (SWEET), that is, VvSWEET10, was strongly expressed at the onset of ripening (véraison) and can improve grape sugar content. VvSWEET10 encodes a plasma membrane-localized transporter, and the heterologous expression of VvSWEET10 indicates that VvSWEET10 is a hexose-affinity transporter and has a broad spectrum of sugar transport functions. VvSWEET10 overexpression in grapevine calli and tomatoes increased the glucose, fructose, and total sugar levels significantly. The RNA sequencing results of grapevine transgenic calli showed that many sugar transporter genes and invertase genes were upregulated and suggest that VvSWEET10 may mediate sugar accumulation. These findings elucidated the role of VvSWEET10 in sugar accumulation and will be beneficial for the improvement of grape berry quality in the future.
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Heiland, Sylvia, Nada Radovanovic, Milan Höfer, Joris Winderickx e Hella Lichtenberg. "Multiple Hexose Transporters ofSchizosaccharomyces pombe". Journal of Bacteriology 182, n. 8 (15 aprile 2000): 2153–62. http://dx.doi.org/10.1128/jb.182.8.2153-2162.2000.
Testo completoAbstract (sommario):
ABSTRACT We have identified a family of six hexose transporter genes (Ght1 to Ght6) in the fission yeastSchizosaccharomyces pombe. Sequence homology toSaccharomyces cerevisiae and mammalian hexose transporters (Hxtp and GLUTp, respectively) and secondary-structure predictions of 12 transmembrane domains for each of the Ght proteins place them into the sugar porter subfamily within the major facilitator superfamily. Interestingly, among this sugar porter family, the emerging S. pombe hexose transporter family clusters are separate from monosaccharide transporters of other yeasts (S. cerevisiae,Kluyveromyces lactis, and Candida albicans) and of humans, suggesting that these proteins form a distinct structural family of hexose transporters. Expression of the Ght1,Ght2, Ght5, and Ght6 genes in theS. cerevisiae mutant RE700A may functionally complement itsd-glucose uptake-deficient phenotype. Northern blot analysis and reverse transcription-PCR showed that among allGht's of S. pombe, Ght5 is the most prominently expressed hexose transporter. Ght1p, Ght2p, and Ght5p displayed significantly higher specificities for d-glucose than for d-fructose. Analysis of the previously describedS. pombe d-glucose transport-deficient mutant YGS-5 revealed that this strain is defective in the Ght1,Ght5, and Ght6 genes. Based on an analysis of three S. pombe strains bearing single or double mutations in Ght3 and Ght4, we conclude that the Ght3p function is required for d-gluconate transport in S. pombe. The function of Ght4p remains to be clarified. Ght6p exhibited a slightly higher affinity to d-fructose than tod-glucose, and among the Ght's it is the transporter with the highest specificity for d-fructose.
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Sujan, SMA, MS Jamal, MA Asad e ANM Fakhruddin. "Bio-ethanol production from Jatropha curcus". Bangladesh Journal of Scientific and Industrial Research 54, n. 1 (25 marzo 2019): 39–46. http://dx.doi.org/10.3329/bjsir.v54i1.40729.
Testo completoAbstract (sommario):
Separate hydrolysis and fermentation (SHF) were employed to produce bio-ethanol from the jatropha stem and husk. This study investigates the favorable condition required to improve yield of monomeric sugars. Substrate was pretreated physically at first through cutter mill and subsequently by ball milling. Acremonium cellulase and optimash BG hydrolyzed the pretreated sample into fermentable sugars. In condition of 10% substrate concentration, ball milling for 60 min and 4 FPU/g enzyme loading and optimum sugar yield were observed. By comparison, jatropha stem is more favorable feedstock compared to jatropha husk in terms of both inherent sugar composition and sugar yield in enzymatic saccharification (hydrolysis). Yeast Saccharomyces cerevisiae, capable of converting hexose sugars into ethanol,was utilized in fermentation step. It was possible to extract 0.14 L and 0.20 L of ethanol per kg of dry substrate-based jatropha husk and jatropha stem, respectively.
Bangladesh J. Sci. Ind. Res.54(1), 39-46, 2019
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Fourie, J. F., e G. Holz. "Effects of Fruit and Pollen Exudates on Growth of Botrytis cinerea and Infection of Plum and Nectarine Fruit". Plant Disease 82, n. 2 (febbraio 1998): 165–70. http://dx.doi.org/10.1094/pdis.1998.82.2.165.
Testo completoAbstract (sommario):
Sugars in exudates from Harry Pickstone plum and Sunlite nectarine fruit and from pollen of weeds commonly found in orchards were determined by gas-liquid chromatography, and their effect on the development of Botrytis cinerea was determined in vitro and in vivo. Fructose, glucose, and sorbitol were the only sugars detected in exudates of immature fruit. They occurred at low concentrations, but their concentration generally increased as fruit ripened. Sucrose was first detected during maturation. In nectarine, an increase in sugar concentration, especially sucrose, was pronounced during the period of rapid cell enlargement, which occurred approximately 2 weeks before harvest. Absorbance readings of culture media amended with sugar indicated that the hexose sugars (fructose and glucose) and sucrose did not markedly influence growth of B. cinerea at concentrations below 0.22 and 0.12 mM, respectively. The hexose sugars caused a steady increase in growth when supplied at concentrations in excess of 0.44 mM, and sucrose caused a steady increase in growth at 0.23 mM. The stimulatory effect of fruit exudates on growth of B. cinerea on glass slides coincided with the period of rapid sugar release from the fruit and the shift in susceptibility to decay. Only fructose (1.72 mM) and glucose (0.72 mM) were detected in nectarine pollen exudates. Pollen exudates from weeds stimulated fungal growth and significantly increased the aggressiveness of the pathogen on plum and nectarine fruit when added to conidia during the last 4 weeks prior to the picking-ripe stage. The study showed that changes in the composition of nectarine and plum fruit exudates may contribute to the late-season susceptibility of these fruit to B. cinerea infection.
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Ouattara, Badiori, Idriss Sermé, Korodjouma Ouattara, Michel P. Sédogo e Hassan Bismark Nacro. "Cropping System Effects on Soil Monosaccharides in Western Burkina Faso". Journal of Agricultural Studies 5, n. 4 (20 novembre 2017): 97. http://dx.doi.org/10.5296/jas.v5i4.11985.
Testo completoAbstract (sommario):
Labile pools of soil organic matter (SOM), including soil sugars, are important to the formation and stabilization of soil aggregates and to microbial activity and nutrient cycling. The effects of cropping systems at farm level in tropical areas on SOM labile pool dynamics have not been adequately studied and the results are sparse and inconsistent. The objective of this study was to determine the effects of soil management intensity on soil sugar monomers derived from plant debris or microbial activity in cotton (Gossypium herbaceum)-based cropping systems of western Burkina Faso. Thirty-three (33) plots were sampled at 0-15 cm soil depth considering field-fallow successions and tillage intensity. Two pentose (arabinose, xylose) and four hexose (glucose, galactose, mannose, glucosamine) monomers accounted for 2 to 18% of soil organic carbon (SOC) content. Total sugar content was significantly less with tillage, especially for the hexose monomeric sugars glucose and mannose, the latter of microbial origin. Soil mannose was 63 and 80% less after 10 years of cultivation, without and with annual ploughing respectively, compared with fallow conditions. Soil monosaccharide content was rapidly restored with fallow and soon approached the equilibrium level observed under old fallow lands. Therefore, the soil monosaccharides, in particular galactose and mannose from microbial synthesis are early indicators of changes in SOC.
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KOMOR, Ewald, Christian SCHOBERT e Bong-Heuy CHO. "Sugar specificity and sugar-proton interaction for the hexose-proton-symport system of Chlorella". European Journal of Biochemistry 146, n. 3 (febbraio 1985): 649–56. http://dx.doi.org/10.1111/j.1432-1033.1985.tb08700.x.
Testo completo
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Bazer, Fuller, Jinyoung Kim, Gwonhwa Song e Guoyao Wu. "Fructose: A Hexose Sugar in Search of a Functional Role." Biology of Reproduction 87, Suppl_1 (1 agosto 2012): 395. http://dx.doi.org/10.1093/biolreprod/87.s1.395.
Testo completo
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Verlinden, Sven, Silvanda M. Silva, Robert C. Herner e Randolph M. Beaudry. "Time-dependent Changes in the Longitudinal Sugar and Respiratory Profiles of Asparagus Spears During Storage at 0 °C". Journal of the American Society for Horticultural Science 139, n. 4 (luglio 2014): 339–48. http://dx.doi.org/10.21273/jashs.139.4.339.
Testo completoAbstract (sommario):
The rate of respiration and the concentrations of sucrose, glucose, and fructose were measured along the length of intact asparagus (Asparagus officinalis cv. Jersey Giant) spears during storage at 0 °C. Carbon dioxide production by each of five sections along the spear was initially high but underwent a rapid and extensive decline within the first 24 hours after harvest with the rate of decline slowing thereafter. The respiration rate was highest at the tip (Section 1), decreasing as the distance from the tip increased (Sections 2 through 5 with Section 5 being more basal). Initially, the respiration rate of the tip was approximately four times that of the base, but after 23 days at 0 °C, the respiration rate of the tip was only twice that of the base. Sugar levels were measured in Sections 1 through 4. Sugar levels declined with time, but increased, unlike respiration, with distance from the tip. Sucrose underwent a rapid decline within the first 24 hours of storage in the tip and Sections 3 and 4. Sucrose depletion was most extensive in the tip, reaching more than 95% by Day 23. Glucose underwent the most rapid decline in Section 2. The relatively higher rate of glucose depletion in Section 2, the zone of rapid cell elongation, may have been to support a relatively higher rate of cell wall biosynthesis in this section. For the first day after harvest, sugar depletion far outstripped hexose equivalents respired as CO2. Afterward, however, the rate of respiration (as hexose equivalents) was similar to the rate of sugar depletion for all sections except the most basipetal, which lost carbohydrate faster than could be accounted for by respired CO2. The data suggest that hexoses were exported from more basipetal tissues to support the metabolic activity of more acropetal sections.
21
Lecourieux, Fatma, David Lecourieux, Céline Vignault e Serge Delrot. "A Sugar-Inducible Protein Kinase, VvSK1, Regulates Hexose Transport and Sugar Accumulation in Grapevine Cells". Plant Physiology 152, n. 2 (18 novembre 2009): 1096–106. http://dx.doi.org/10.1104/pp.109.149138.
Testo completo
22
Hill, L. M., e S. Rawsthorne. "Carbon supply for storage-product synthesis in developing seeds of oilseed rape". Biochemical Society Transactions 28, n. 6 (1 dicembre 2000): 667–69. http://dx.doi.org/10.1042/bst0280667.
Testo completoAbstract (sommario):
The aim of this work was to find out how the sugars in the endosperm of oilseed rape contribute to the flux of oil synthesis. While the hexose content of the liquid endosperm decreased during development the sucrose content increased. It is important to understand the relative rates of use of the endosperm sugars for two reasons. Firstly we need to know which sugars are used, and at what stages in development, in order to understand the roles of enzymes involved in their metabolism. Secondly, changes in sugar concentration have been implicated in the regulation of expression of genes determining storage-product synthesis [see Weber, Borisjuk and Wobus (1997) Trends Plant Sci. 2, 169–174, for review]. The rate of consumption of sugar is one factor governing its concentration. We present data showing both the concentration-dependence of conversion of sugar to oil, and the in vivo concentrations of sugars; we relate these data sets to each other and discuss the effects of the intracellular pool of sucrose. Glucose, fructose and sucrose are all substrates for oil synthesis, but the rates of their use (particularly sucrose) are underestimated because of dilution by sucrose from the intracellular pool.
23
Mitchell, Wilfrid J. "The Phosphotransferase System in Solventogenic Clostridia". Journal of Molecular Microbiology and Biotechnology 25, n. 2-3 (2015): 129–42. http://dx.doi.org/10.1159/000375125.
Testo completoAbstract (sommario):
The acetone-butanol-ethanol fermentation employing solventogenic clostridia was a major industrial process during the 20th century, but declined for economic reasons. In recent times, interest in the process has been revived due to the perceived potential of butanol as a superior biofuel. Redevelopment of an efficient fermentation process will require a detailed understanding of the physiology of carbohydrate utilization by the bacteria. Genome sequences have revealed that, as in other anaerobes, the phosphotransferase system (PTS) and associated regulatory functions are likely to play an important role in sugar uptake and its regulation. The genomes of <i>Clostridium acetobutylicum</i> and <i>C. beijerinckii</i> encode 13 and 43 phosphotransferases, respectively. Characterization of clostridial phosphotransferases has demonstrated that they are involved in the uptake and phosphorylation of hexoses, hexose derivatives and disaccharides, although the functions of many systems remain to be determined. Glucose is a dominant sugar which represses the utilization of other carbon sources, including the non-PTS pentose sugars xylose and arabinose, by the clostridia. Targeting of the CcpA-dependent mechanism of carbon catabolite repression has been shown to be an effective strategy for reducing the repressive effects of glucose, indicating potential for developing strains with improved fermentation performance.
24
Liu, Xuan, Paul W. Robinson, Monica A. Madore, Guy W. Witney e Mary Lu Arpaia. "`Hass' Avocado Carbohydrate Fluctuations. II. Fruit Growth and Ripening". Journal of the American Society for Horticultural Science 124, n. 6 (novembre 1999): 676–81. http://dx.doi.org/10.21273/jashs.124.6.676.
Testo completoAbstract (sommario):
Changes in soluble sugar and starch reserves in avocado (Persea americana Mill. on `Duke 7' rootstock) fruit were followed during growth and development and during low temperature storage and ripening. During the period of rapid fruit size expansion, soluble sugars accounted for most of the increase in fruit tissue biomass (peel: 17% to 22%, flesh: 40% to 44%, seed: 32% to 41% of the dry weight). More than half of the fruit total soluble sugars (TSS) was comprised of the seven carbon (C7) heptose sugar, D-mannoheptulose, and its polyol form, perseitol, with the balance being accounted for by the more common hexose sugars, glucose and fructose. Sugar content in the flesh tissues declined sharply as oil accumulation commenced. TSS declines in the seed were accompanied by a large accumulation of starch (≈30% of the dry weight). During postharvest storage at 1 or 5 °C, TSS in peel and flesh tissues declined slowly over the storage period. Substantial decreases in TSS, and especially in the C7 sugars, was observed in peel and flesh tissues during fruit ripening. These results suggest that the C7 sugars play an important role, not only in metabolic processes associated with fruit development, but also in respiratory processes associated with postharvest physiology and fruit ripening.
25
Stoop, Johan M. H., e David M. Pharr. "Growth Substrate and Nutrient Salt Environment Alter Mannitol-to-Hexose Partitioning in Celery Petioles". Journal of the American Society for Horticultural Science 119, n. 2 (marzo 1994): 237–42. http://dx.doi.org/10.21273/jashs.119.2.237.
Testo completoAbstract (sommario):
The fleshy parenchyma tissue of celery [Apium graveolens L. var. dulce (Mill.) Pers.] petioles is the major storage tissue for the sugar alcohol mannitol and for the hexoses, glucose and fructose. In this study, we found that plants grown in the soilless mixture, Promix, fertilized weekly with a nutrient solution, or grown in a hydroponic container culture, differed in carbohydrate composition. However, plant growth was not affected. Higher mannitol and lower hexose concentrations were present in petioles from plants grown hydroponically. This was true in petioles that did not differ in total soluble carbohydrate concentration. The ratio of mannitol to hexose concentration in petioles was ≈2-fold higher for hydroponically grown plants compared to Promix-grown plants, and the higher ratio was maintained during the entire 12-week experimental period. Carbohydrate partitioning was also affected by petiole development within the plant. Sucrose and hexose concentrations were highest in mature petioles, whereas mannitol was relatively high in all petioles except the oldest ones. Because the mineral solution applied to the Promix-grown plants had a lower total salt concentration compared to hydroponically grown plants, we postulated that the salt concentration of the mineral solution might be an important factor affecting C partitioning in celery petioles. When plants were grown hydroponically at two different salt concentrations [electrical conductivity (EC) = 2.7 and 6.0 mS·cm-1], high mannitol-to-hexose ratios were observed in celery petioles of plants grown at high salt concentration (EC = 6.0 mS·cm-1), a result supporting the hypothesis that the salt environment might alter mannitol and hexose concentrations in a coordinated way. These data are consistent with the hypothesis that elevated mannitol levels may be a significant component of plant adjustment to salt stress, possibly adding osmotic adjustment and preventing inactivation of metabolic processes.
26
Rossouw, Gerhard C., Jason P. Smith, Celia Barril, Alain Deloire e Bruno P. Holzapfel. "Implications of the Presence of Maturing Fruit on Carbohydrate and Nitrogen Distribution in Grapevines under Postveraison Water Constraints". Journal of the American Society for Horticultural Science 142, n. 2 (marzo 2017): 71–84. http://dx.doi.org/10.21273/jashs03982-16.
Testo completoAbstract (sommario):
Grapevine (Vitis vinifera) berries are sugar and nitrogen (N) sinks between veraison and fruit maturity. Limited photoassimilation, often caused by water constraints, induces reserve total nonstructural carbohydrate (TNC) remobilization, contributing to berry sugar accumulation, while fruit N accumulation can be affected by vine water supply. Although postveraison root carbohydrate remobilization toward the fruit has been identified through 14C tracing studies, it is still unclear when this remobilization occurs during the two phases of berry sugar accumulation (rapid and slow). Similarly, although postveraison N reserve mobilization toward the fruit has been reported, the impact of water constraints during berry N accumulation on its translocation from the different grapevine organs requires clarification. Potted grapevines were grown with or without fruit from the onset of veraison. Vines were irrigated to sustain water constraints, and fortnightly root, trunk, shoot, and leaf structural biomass, starch, soluble sugar, total N, and amino N concentrations were determined. The fruit sugar and N accumulation was also assessed. Root starch depletion coincided with root sucrose and hexose accumulation during peak berry sugar accumulation. Defruiting at veraison resulted in continuous root growth, earlier starch storage, and root hexose accumulation. Leaf N depletion coincided with fruit N accumulation, while the roots of defruited vines accumulated N reserves. Root growth, starch, and N reserve accumulation were affected by maturing fruit during water constraints. Root starch is an alternative source to support fruit sugar accumulation, resulting in reserve starch depletion during rapid fruit sugar accumulation, while root starch refills during slow berry sugar accumulation. On the other hand, leaf N is a source toward postveraison fruit N accumulation, and the fruit N accumulation prevents root N storage.
27
Atanassova, Rossitza, Marina Leterrier, Cécile Gaillard, Alice Agasse, Emeric Sagot, Pierre Coutos-Thévenot e Serge Delrot. "Sugar-Regulated Expression of a Putative Hexose Transport Gene in Grape". Plant Physiology 131, n. 1 (1 gennaio 2003): 326–34. http://dx.doi.org/10.1104/pp.009522.
Testo completo
28
Ha-Tran, Dung Minh, Trinh Thi My Nguyen, Shou-Chen Lo e Chieh-Chen Huang. "Utilization of Monosaccharides by Hungateiclostridium thermocellum ATCC 27405 through Adaptive Evolution". Microorganisms 9, n. 7 (4 luglio 2021): 1445. http://dx.doi.org/10.3390/microorganisms9071445.
Testo completoAbstract (sommario):
Hungateiclostridium thermocellum ATCC 27405 is a promising bacterium for consolidated bioprocessing with a robust ability to degrade lignocellulosic biomass through a multienzyme cellulosomal complex. The bacterium uses the released cellodextrins, glucose polymers of different lengths, as its primary carbon source and energy. In contrast, the bacterium exhibits poor growth on monosaccharides such as fructose and glucose. This phenomenon raises many important questions concerning its glycolytic pathways and sugar transport systems. Until now, the detailed mechanisms of H. thermocellum adaptation to growth on hexose sugars have been relatively poorly explored. In this study, adaptive laboratory evolution was applied to train the bacterium in hexose sugars-based media, and genome resequencing was used to detect the genes that got mutated during adaptation period. RNA-seq data of the first culture growing on either fructose or glucose revealed that several glycolytic genes in the Embden–Mayerhof–Parnas pathway were expressed at lower levels in these cells than in cellobiose-grown cells. After seven consecutive transfer events on fructose and glucose (~42 generations for fructose-adapted cells and ~40 generations for glucose-adapted cells), several genes in the EMP glycolysis of the evolved strains increased the levels of mRNA expression, accompanied by a faster growth, a greater biomass yield, a higher ethanol titer than those in their parent strains. Genomic screening also revealed several mutation events in the genomes of the evolved strains, especially in those responsible for sugar transport and central carbon metabolism. Consequently, these genes could be applied as potential targets for further metabolic engineering to improve this bacterium for bio-industrial usage.
29
Harrington, Gregory N., Katherine E. Dibley, Raymond J. Ritchie, Christina E. Offler e John W. Patrick. "Hexose uptake by developing cotyledons of Vicia faba: physiological evidence for transporters of differing affinities and specificities". Functional Plant Biology 32, n. 11 (2005): 987. http://dx.doi.org/10.1071/fp05081.
Testo completoAbstract (sommario):
Cotyledons of broad bean (Vicia faba L.) develop in an apoplasmic environment that shifts in composition from one dominated by hexoses to one dominated by sucrose. During the latter phase of development, sucrose / H+ symporter activity and expression is restricted to cotyledon epidermal transfer cell complexes that support sucrose fluxes that are 8.5-fold higher than those exhibited by the storage parenchyma. In contrast, the flux difference between these cotyledon tissues is only 1.7-fold for hexoses. Glucose and fructose uptake was shown to be sensitive to PCMBS and phloridzin, both of which slow H+-sugar transport. A low Km (or high affinity transporter, HAT) mechanism transports glucose and glucose-analogues exclusively. No HAT system for fructose could be found. A high Km (low affinity transporter, LAT) mechanism transports a broader range of hexoses, including glucose and fructose. Consistent with glucose and fructose transport being H+-coupled, their uptake was inhibited by dissipating the proton motive force (pmf) by treating cotyledons with carbonyl cyanide m-chlorophenol hydrazone, propionic acid or tetraphenylphosphonium ion. Erythrosin B inhibited hexose uptake, indicating a role for the P-type H+-ATPase in establishing the pmf. It is concluded that H+-coupled glucose and fructose transport mechanisms occur at plasma membranes of dermal transfer cell complexes and storage parenchyma cells. These transport mechanisms are active during pre- and storage phases of cotyledon development. However, hexose symport only makes a quantitative contribution to cotyledon biomass gain during the pre-storage stage of development.
30
Nicolson, Susan W., e Ben-Erik Van Wyk. "Nectar Sugars in Proteaceae: Patterns and Processes". Australian Journal of Botany 46, n. 4 (1998): 489. http://dx.doi.org/10.1071/bt97039.
Testo completoAbstract (sommario):
The nectar sugar composition is presented for 147 species from 16 genera of South African and Australian Proteaceae. Patterns associated with flower age, different plants and populations, plant phylogeny and pollination have been examined. In addition to the usual three nectar sugars (sucrose, fructose and glucose), the nectar of Protea and Faurea contains the pentose sugar xylose at concentrations of up to 39% of total sugar. Xylose has not previously been reported from floral nectar and is absent from the nectar of Adenanthos, Banksia, Brabejum, Dryandra, Grevillea, Hakea, Lambertia, Leucospermum, Macadamia, Mimetes, Orothamnus, Paranomus, Stenocarpus and Telopea. Most genera and species have hexose-dominant nectar, but within the large genera Banksia, Grevillea, Leucospermum and Protea some of the seemingly more derived species have sucrose-dominant nectar. This interesting dichotomy of low versus high sucrose is of diagnostic value at the species level and indicative of phylogenetic relationships within the larger genera. At the generic level, the presence of xylose is a convincing synapomorphy for Protea and Faurea. Studies of physiological processes (e.g. enzyme activities) and ecological processes (e.g. pollination) may help to explain some of the conservative and taxonomically interesting nectar sugar patterns.
31
Ma, Hongmei, Henrik H. Albert, Robert Paull e Paul H. Moore. "Metabolic engineering of invertase activities in different subcellular compartments affects sucrose accumulation in sugarcane cells". Functional Plant Biology 27, n. 11 (2000): 1021. http://dx.doi.org/10.1071/pp00029.
Testo completoAbstract (sommario):
Transgenic sugarcane (Saccharum officinarum L.) lines were created to express altered invertase isoform activity to elucidate the role(s) of invertase in the sucrose accumulation process. A sugarcane soluble acid invertase cDNA (SCINVm, AF062734) in the antisense orientation was used to decrease invertase activity. The Saccharomyces cerevisiae invertase gene (SUC2), fused with appropriate targeting elements, was used to increase invertase activity in the apoplast, cytoplasm and vacuole. A callus/liquid culture system was established to evaluate change in invertase activity and sugar concentration in the transgenic lines. Increased invertase activity in the apoplast led to rapid hydrolysis of sucrose and rapid increase of hexose in the medium. The cellular hexose content increased dramatically and the sucrose level decreased. Cells with higher cytoplasmic invertase activity did not show a significant change in the sugar composition in the medium, but did significantly reduce the sucrose content in the cells. Transformation with the sugarcane antisense acid invertase gene produced a cell line with moderate inhibition of soluble acid invertase activity and a 2-fold increase in sucrose accumulation. Overall, intracellular and extracellular sugar composition was very sensitive to the change in invertase activities. Lowering acid invertase activity increased sucrose accumulation.
32
Nadai, Chiara, Giulia Crosato, Alessio Giacomini e Viviana Corich. "Different Gene Expression Patterns of Hexose Transporter Genes Modulate Fermentation Performance of Four Saccharomyces cerevisiae Strains". Fermentation 7, n. 3 (23 agosto 2021): 164. http://dx.doi.org/10.3390/fermentation7030164.
Testo completoAbstract (sommario):
In Saccharomyces cerevisiae, the fermentation rate and the ability to complete the sugar transformation process depend on the glucose and fructose transporter set-up. Hexose transport mainly occurs via facilitated diffusion carriers and these are encoded by the HXT gene family and GAL2. In addition, FSY1, coding a fructose/H+ symporter, was identified in some wine strains. This little-known transporter could be relevant in the last part of the fermentation process when fructose is the most abundant sugar. In this work, we investigated the gene expression of the hexose transporters during late fermentation phase, by means of qPCR. Four S. cerevisiae strains (P301.9, R31.3, R008, isolated from vineyard, and the commercial EC1118) were considered and the transporter gene expression levels were determined to evaluate how the strain gene expression pattern modulated the late fermentation process. The very low global gene expression and the poor fermentation performance of R008 suggested that the overall expression level is a determinant to obtain the total sugar consumption. Each strain showed a specific gene expression profile that was strongly variable. This led to rethinking the importance of the HXT3 gene that was previously considered to play a major role in sugar transport. In vineyard strains, other transporter genes, such as HXT6/7, HXT8, and FSY1, showed higher expression levels, and the resulting gene expression patterns properly supported the late fermentation process.
33
Ysart, G. E., e R. M. Mason. "Serum factors, growth factors and UDP-sugar metabolism in bovine articular cartilage chondrocytes". Biochemical Journal 303, n. 3 (1 novembre 1994): 713–21. http://dx.doi.org/10.1042/bj3030713.
Testo completoAbstract (sommario):
1. The effect of different batches of fetal bovine serum and of growth factors on [35S]sulphate incorporation into glycosaminoglycans and on UDP-sugar pools in explant cultures of bovine articular cartilage was investigated. 2. [35S]Sulphate incorporation was variably stimulated between 1.2- and 3.5-fold by four different batches of serum. The UDP-glucuronate pool size expanded 4.3-6.5-fold in the presence of serum, even in those cultures in which little stimulation of [35S]sulphate incorporation occurred. The UDP-N-acetylhexosamine and UDP-hexose pools expanded by about 1.5- and 2.0-fold respectively in the presence of serum. UDP-xylose was not detected. 3. Equilibrium-labelling and pulse-chase experiments with D-[1-3H]glucose indicated that the rate of flux through the UDP-sugar pools was unaffected by serum. UDP-hexose, UDP-N-acetylhexosamine and UDP-glucuronate have approximate half-lives (t1/2) of 7, 12 and 3-4 min respectively. At equilibrium, the 3H specific activities of UDP-hexose and UDP-N-acetylhexosamine were very similar but that for the UDP-glucuronate pool was much higher, especially in serum-supplemented cultures. The results suggest that UDP-glucuronate synthesis occurs via a pathway which is independent of the main UDP-hexose pathway. 4. Supplementing cultures with heat-treated serum had no effect on the serum-induced expansion of UDP-sugar pools but stimulation of [35S]sulphate incorporation into glycosaminoglycans was 50% lower than for native serum. Acid-treated serum promoted a 2-fold expansion of the UDP-glucuronate and UDP-N-acetylhexosamine pool over that obtained with native serum but was 20% less effective in stimulating [35S]sulphate incorporation than the latter. Prior dialysis of serum had no effect on its modulatory action on either [35S]sulphate incorporation or on the size of UDP-sugar pools. 5. Insulin-like growth factor 1 (IGF-1), transforming growth factor beta-1 (TGF beta-1), platelet-derived growth factor (PDGF) (BB homodimer) and epidermal growth factor (EGF) all stimulated [35S]sulphate incorporation into glycosaminoglycans as expected. The UDP-glucuronate pool expanded by 1.5- and 2.0-fold in the presence of IGF-1 and TGF beta-1 respectively, and by about 1.8-fold in the presence of PDGF or EGF. None of the factors investigated, or combinations of IGF-1 and TGF beta-1 or IGF-1 and EGF, stimulated expansion of the UDP-glucuronate pool to the same extent as native serum.(ABSTRACT TRUNCATED AT 400 WORDS)
34
Leandro, Maria José, Hana Sychrová, Catarina Prista e Maria C. Loureiro-Dias. "The osmotolerant fructophilic yeast Zygosaccharomyces rouxii employs two plasma-membrane fructose uptake systems belonging to a new family of yeast sugar transporters". Microbiology 157, n. 2 (1 febbraio 2011): 601–8. http://dx.doi.org/10.1099/mic.0.044446-0.
Testo completoAbstract (sommario):
Owing to its high resistance to weak-acid preservatives and extreme osmotolerance, Zygosaccharomyces rouxii is one of the main spoilage yeasts of sweet foods and beverages. In contrast with Saccharomyces cerevisiae, Z. rouxii is a fructophilic yeast; it consumes fructose faster than glucose. So far, to our knowledge, no specific Z. rouxii proteins responsible for this fructophilic behaviour have been characterized. We have identified two genes encoding putative fructose transporters in the Z. rouxii CBS 732 genome. Heterologous expression of these two Z. rouxii ORFs in a S. cerevisiae strain lacking its own hexose transporters (hxt-null) and subsequent kinetic analysis of sugar transport showed that both proteins are functionally expressed at the plasma membrane: ZrFfz1 is a high-capacity fructose-specific facilitator (K m∼400 mM and V max∼13 mmol h−1 g−1) and ZrFfz2 is a facilitator transporting glucose and fructose with similar capacity and affinity (K m∼200 mM and V max∼4 mmol h−1 g−1). These two proteins together with the Zygosaccharomyces bailii Ffz1 fructose-specific transporter belong to a new family of sugar transport systems mediating the uptake of hexoses via the facilitated diffusion mechanism, and are more homologous to drug/H+ antiporters (regarding their primary protein structure) than to other yeast sugar transporters of the Sugar Porter family.
35
Heluane, Humberto, Matthew R. Evans, Sue F. Dagher e José M. Bruno-Bárcena. "Meta-Analysis and Functional Validation of Nutritional Requirements of Solventogenic Clostridia Growing under Butanol Stress Conditions and Coutilization of d-Glucose and d-Xylose". Applied and Environmental Microbiology 77, n. 13 (20 maggio 2011): 4473–85. http://dx.doi.org/10.1128/aem.00116-11.
Testo completoAbstract (sommario):
ABSTRACTRecent advances in systems biology, omics, and computational studies allow us to carry out data mining for improving biofuel production bioprocesses. Of particular interest are bioprocesses that center on microbial capabilities to biotransform both the hexose and pentose fractions present in crop residues. This called for a systematic exploration of the components of the media to obtain higher-density cultures and more-productive fermentation operations than are currently found. By using a meta-analysis approach of the transcriptional responses to butanol stress, we identified the nutritional requirements of solvent-tolerant strainClostridium beijerinckiiSA-1 (ATCC 35702). The nutritional requirements identified were later validated using the chemostat pulse-and-shift technique.C. beijerinckiiSA-1 was cultivated in a two-stage single-feed-stream continuous production system to test the proposed validated medium formulation, and the coutilization ofd-glucose andd-xylose was evaluated by taking advantage of the well-known ability of solventogenic clostridia to utilize a large variety of carbon sources such as mono-, oligo-, and polysaccharides containing pentose and hexose sugars. Our results indicated thatC. beijerinckiiSA-1 was able to coferment hexose/pentose sugar mixtures in the absence of a glucose repression effect. In addition, our analysis suggests that the solvent and acid resistance mechanisms found in this strain are differentially regulated compared to strain NRRL B-527 and are outlined as the basis of the analysis toward optimizing butanol production.
36
Brigham, Christopher J., e Michael H. Malamy. "Characterization of the RokA and HexA Broad-Substrate-Specificity Hexokinases from Bacteroides fragilis and Their Role in Hexose and N-Acetylglucosamine Utilization". Journal of Bacteriology 187, n. 3 (1 febbraio 2005): 890–901. http://dx.doi.org/10.1128/jb.187.3.890-901.2005.
Testo completoAbstract (sommario):
ABSTRACT Bacteroides fragilis, a human gastrointestinal commensal and an opportunistic pathogen, utilizes simple and complex sugars and polysaccharides for growth in the large intestine and at sites of infection. Because B. fragilis lacks transport-linked sugar phosphorylation systems, cytoplasmic kinase(s) was expected to be required for the phosphorylation of hexoses and hexosamines. We have now identified two hexose kinases that are important for growth of B. fragilis on glucose, mannose, and other sugars. One kinase (RokA), a member of the ROK family of proteins, was found to be the sole kinase for activation of N-acetyl-d-glucosamine (NAG). The other kinase (HexA) is responsible for the majority of the glucose kinase activity in the cell, although a hexA deletion mutant strain was not defective for growth on any substrate tested. Deletion of both the rokA and hexA kinase genes resulted in inability of the cell to use glucose, mannose, NAG, and many other sugars. We purified RokA and determined its approximate molecular mass to be 36.5 kDa. The purified RokA protein was shown to phosphorylate several substrates, including glucose, NAG, and mannose, but not N-acetylmannosamine or N-acetylneuraminic acid. Phylogenetic analysis of RokA showed that it is most similar to kinases from the Cytophaga-Flavibacterium-Bacteroides group, while HexA was most similar to other bacterial hexokinases and eukaryotic hexokinases.
37
Kelly, F. H. C. "Phase equilibria in sugar solutions. II. Ternary systems of water-sucrose-hexose". Journal of Applied Chemistry 4, n. 8 (4 maggio 2007): 405–7. http://dx.doi.org/10.1002/jctb.5010040802.
Testo completo
38
Campbell, Richard J., Richard D. Fell e Richard P. Marini. "Canopy Position, Defoliation, and Girdling Influence Apple Nectar Production". HortScience 26, n. 5 (maggio 1991): 531–32. http://dx.doi.org/10.21273/hortsci.26.5.531.
Testo completoAbstract (sommario):
Flowering spurs located at interior and exterior canopy positions of `Stay-man' and `Delicious' apple (Malus domestics Borkh.) trees were girdled and/or defoliated to determine the influence on nectar production and composition. Nectar volume was less at exterior than interior canopy positions for `Delicious', but not for `Stayman'. Girdling suppressed nectar production by 92% and reduced the sugar concentration of the remaining nectar. Defoliation of nongirdled spurs had no effect on nectar sugar concentration, but defoliation of girdled spurs reduced nectar sugar concentration by 24%. Relative percentages of sucrose, glucose, and fructose, and the sucrose: hexose ratio were unaffected by any treatment. Nectar production of nongirdled spurs did not depend on the presence of spur leaves.
39
Caspari, T., A. Will, M. Opekarová, N. Sauer e W. Tanner. "Hexose/H+ symporters in lower and higher plants." Journal of Experimental Biology 196, n. 1 (1 novembre 1994): 483–91. http://dx.doi.org/10.1242/jeb.196.1.483.
Testo completoAbstract (sommario):
A well-studied transporter of plant cells is the hexose/H+ symporter of the unicellular alga Chlorella kessleri. Its properties, studied in vivo, are briefly summarized. In part, they are atypical and it has been suggested that this porter acts in an asymmetric way. Three genes coding for Chlorella hexose transport activity have been identified (HUP1, HUP2 and HUP3). HUP1 cDNA expressed in a mutant of Schizosaccharomyces pombe not transporting any D-glucose has been studied in detail. Several mutants with changed Km values for substrate were obtained, some by random polymerase chain reaction mutation and selection for decreased sensitivity towards the toxic sugar 2-deoxyglucose, some by site-directed mutagenesis. The amino acids affected clustered in the centre of the putative transmembrane helices V, VII and XI. Large families of hexose transporter genes are found in higher plants (Arabidopsis, Chenopodium, Ricinus). Their functional role is discussed. Finally, the progress made in studying plant transporters in a vesicle system energized by cytochrome c oxidase is summarized.
40
LAI, LISA X., e RENATA BURA. "The sulfite mill as a sugar-flexible future biorefinery". August 2012 11, n. 8 (1 settembre 2012): 27–35. http://dx.doi.org/10.32964/tj11.8.27.
Testo completoAbstract (sommario):
The production of single- and mixed-sugar streams and their conversion to bioproducts were studied, using sulfite pulping streams as feedstocks. Sulfite pulp, sludge, and spent sulfite liquor are concurrently generated alongside of bleached pulp, and the pulping process renders pretreatment of solid streams unnecessary. Streams were converted separately; however, due to their low production volume, solid and liquid streams were also combined as a means to increase the quantity of starting feedstock. Spent sulfite liquor, comprising mostly monomeric hexose and pentose sugars, was directly fermented to ethanol and xylitol with Candida guilliermondii. Single-sugar streams were generated through hydrolysis of pulp and sludge in water, followed by fermentation to ethanol with Saccharomyces cerevisiae. Mixed-sugar streams were generated through both separate hydrolysis and fermentation and simultaneous saccharification and fermentation of pulp and sludge in spent sulfite liquor using S. cerevisiae. The best single-sugar source was obtained by hydrolysis of pulp in water, which produced 78.8 g/L of glucose after 96 h. The glucose concentration from hydrolysis of sludge in water was lower (33.5 g/L). Both of these streams were easily converted to ethanol, with yields of 77.8% and 76.2%, respectively. Hydrolyzability of solids was the limiting factor in separate hydrolysis and fermentation conversion of pulp and sludge in water, but hydrolyzability of sludge was not affected when mixed with spent sulfite liquor.
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Guimarães, Pedro M. R., Jyri-Pekka Multanen, Lucília Domingues, José A. Teixeira e John Londesborough. "Stimulation of Zero-trans Rates of Lactose and Maltose Uptake into Yeasts by Preincubation with Hexose To Increase the Adenylate Energy Charge". Applied and Environmental Microbiology 74, n. 10 (31 marzo 2008): 3076–84. http://dx.doi.org/10.1128/aem.00188-08.
Testo completoAbstract (sommario):
ABSTRACT Initial rates of sugar uptake (zero-trans rates) are often measured by incubating yeast cells with radiolabeled sugars for 5 to 30 s and determining the radioactivity entering the cells. The yeast cells used are usually harvested from growth medium, washed, suspended in nutrient-free buffer, and stored on ice before they are assayed. With this method, the specific rates of zero-trans lactose uptake by Kluyveromyces lactis or recombinant Saccharomyces cerevisiae strains harvested from lactose fermentations were three- to eightfold lower than the specific rates of lactose consumption during fermentation. No significant extracellular β-galactosidase activity was detected. The ATP content and adenylate energy charge (EC) of the yeasts were relatively low before the [14C]lactose uptake reactions were started. A short (1- to 7-min) preincubation of the yeasts with 10 to 30 mM glucose caused 1.5- to 5-fold increases in the specific rates of lactose uptake. These increases correlated with increases in EC (from 0.6 to 0.9) and ATP (from 4 to 8 μmol·g dry yeast−1). Stimulation by glucose affected the transport V max values, with smaller increases in Km values. Similar observations were made for maltose transport, using a brewer's yeast. These findings suggest that the electrochemical proton potential that drives transport through sugar/H+ symports is significantly lower in the starved yeast suspensions used for zero-trans assays than in actively metabolizing cells. Zero-trans assays with such starved yeast preparations can produce results that seriously underestimate the capacity of sugar/H+ symports. A short exposure to glucose allows a closer approach to the sugar/H+ symport capacity of actively metabolizing cells.
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Zhang, Ping, Wenwen Zhang, Xiangshan Zhou, Peng Bai, James M. Cregg e Yuanxing Zhang. "Catabolite Repression of Aox in Pichia pastoris Is Dependent on Hexose Transporter PpHxt1 and Pexophagy". Applied and Environmental Microbiology 76, n. 18 (23 luglio 2010): 6108–18. http://dx.doi.org/10.1128/aem.00607-10.
Testo completoAbstract (sommario):
ABSTRACT In this work, the identification and characterization of two hexose transporter homologs in the methylotrophic yeast Pichia pastoris, P. pastoris Hxt1 (PpHxt1) and PpHxt2, are described. When expressed in a Saccharomyces cerevisiae hxt-null mutant strain that is unable to take up monosaccharides, either protein restored growth on glucose or fructose. Both PpHXT genes are transcriptionally regulated by glucose. Transcript levels of PpHXT1 are induced by high levels of glucose, whereas transcript levels of PpHXT2 are relatively lower and are fully induced by low levels of glucose. In addition, PpHxt2 plays an important role in glycolysis-dependent fermentative growth, since PpHxt2 is essential for growth on glucose or fructose when respiration is inhibited. Notably, we firstly found that the deletion of PpHXT1, but not PpHXT2, leads to the induced expression of the alcohol oxidase I gene (AOX1) in response to glucose or fructose. We also elucidated that a sharp dropping of the sugar-induced expression level of Aox at a later growth phase is caused mainly by pexophagy, a degradation pathway in methylotrophic yeast. The sugar-inducible AOX1 promoter in an Δhxt1 strain may be promising as a host for the expression of heterologous proteins. The functional analysis of these two hexose transporters is the first step in elucidating the mechanisms of sugar metabolism and catabolite repression in P. pastoris.
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Desai, Tasha A., e Christopher V. Rao. "Regulation of Arabinose and Xylose Metabolism in Escherichia coli". Applied and Environmental Microbiology 76, n. 5 (18 dicembre 2009): 1524–32. http://dx.doi.org/10.1128/aem.01970-09.
Testo completoAbstract (sommario):
ABSTRACT Bacteria such as Escherichia coli will often consume one sugar at a time when fed multiple sugars, in a process known as carbon catabolite repression. The classic example involves glucose and lactose, where E. coli will first consume glucose, and only when it has consumed all of the glucose will it begin to consume lactose. In addition to that of lactose, glucose also represses the consumption of many other sugars, including arabinose and xylose. In this work, we characterized a second hierarchy in E. coli, that between arabinose and xylose. We show that, when grown in a mixture of the two pentoses, E. coli will consume arabinose before it consumes xylose. Consistent with a mechanism involving catabolite repression, the expression of the xylose metabolic genes is repressed in the presence of arabinose. We found that this repression is AraC dependent and involves a mechanism where arabinose-bound AraC binds to the xylose promoters and represses gene expression. Collectively, these results demonstrate that sugar utilization in E. coli involves multiple layers of regulation, where cells will consume first glucose, then arabinose, and finally xylose. These results may be pertinent in the metabolic engineering of E. coli strains capable of producing chemical and biofuels from mixtures of hexose and pentose sugars derived from plant biomass.
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Kelly, F. H. C. "Phase equilibria in sugar solutions. III. Ternary systems of water-hexose-inorganic salt". Journal of Applied Chemistry 4, n. 8 (4 maggio 2007): 407–8. http://dx.doi.org/10.1002/jctb.5010040803.
Testo completo
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Rist, R. J., e R. J. Naftalin. "Dexamethasone inhibits the hexose monophosphate shunt in activated rat peritoneal macrophages by reducing hexokinase-dependent sugar uptake". Biochemical Journal 278, n. 1 (15 agosto 1991): 129–35. http://dx.doi.org/10.1042/bj2780129.
Testo completoAbstract (sommario):
Dexamethasone decreases 2-D-deoxyglucose (2-dGlc) uptake and accumulation into rat peritoneal macrophages in vitro in a concentration- and time-dependent manner (Ki for 1 microM-dexamethasone after a 2 h exposure = 0.71 +/- 0.21 microM; Ki for 0.1 microM-dexamethasone after exposure for 4 h = 0.10 +/- 0.06 microM). The inhibition of 2-dGlc uptake is consistent with a decrease in the coupling between endofacial hexokinase activity and the sugar transporter. The evidence for this is: (1) the Km for zero-trans 2-dGlc uptake in quiescent macrophages was increased by dexamethasone, but there was no significant effect on the Vmax.; (2) dexamethasone increased the rate of exit of sugar from cells preloaded with 2-dGlc; (3). the free sugar accumulation within the cytosol of the cells above the external solution concentration was significantly decreased by dexamethasone. These effects of dexamethasone on 2-dGlc transport were antagonized by simultaneous exposure to the steroid RU 38486 (Ki = 0.04 +/- 0.01 microM; 4 h incubation). Although dexamethasone inhibited zero-trans uptake, the maximum rate of infinite-trans exchange uptake of 2-dGlc into cells preloaded with 3-O-methyl-D-glucose (40 mM) was unaltered by dexamethasone or RU 38486, indicating that the dexamethasone-dependent decrease in zero-trans uptake was not due to a change in the number of transporters in the plasma membrane. Dexamethasone also inhibited the phorbol myristate acetate-induced stimulation of hexose monophosphate shunt (HMPS) activity, and this was reversed by RU 38486. Cytochalasin B, the potent sugar-transport inhibitor, inhibited HMPS activity and 2-d[2,6-3H]Glc uptake equally, indicating a single site of action. By contrast, dexamethasone showed differential inhibition of HMPS activity and 2-d[2,6-3H]Glc uptake, suggesting that it not only acts by decreasing the coupling between hexokinase and sugar transport, but also at one or more additional points.
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Rossouw, Debra, Sue Bosch, Jens Kossmann, Frederik C. Botha e Jan-Hendrik Groenewald. "Downregulation of neutral invertase activity in sugarcane cell suspension cultures leads to a reduction in respiration and growth and an increase in sucrose accumulation". Functional Plant Biology 34, n. 6 (2007): 490. http://dx.doi.org/10.1071/fp06214.
Testo completoAbstract (sommario):
Suspension cultures were used as a model system to investigate sucrose metabolism in four sugarcane (Saccharum spp. interspecific hybrids) cell lines transformed with antisense neutral invertase (NI) constructs. Throughout a 14-day growth cycle two cell lines in which the antisense sequence was under the control of a tandem CaMV-35S: maize ubiquitin promoter showed a strong reduction in NI activity, as well as reduced hexose and increased sucrose concentrations in comparison to the control line. In lines where the antisense NI sequence was under the control of the weaker CaMV-35S promoter alone, changes in enzyme activity and sugar concentrations were intermediate to those of the more strongly inhibited lines and the control. In comparison to the control line, a higher sucrose to hexose ratio, i.e. increased purity, was obtained in all the lines with reduced NI activity. The in vivo rate of sucrose hydrolysis was reduced in the transgenic lines, suggesting a concomitant reduction in the flux through the ‘futile cycle’ of sucrose breakdown and re-synthesis. Differences between the transgenic cultures and the control were most pronounced during the early stages of the growth cycle and tapered off as the cultures matured. The transgenic cultures displayed impaired growth characteristics suggesting that the growth rate of these cells was retarded because of the reduced availability of hexoses for respiration.
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Grochowski, Laura L., Huimin Xu e Robert H. White. "Ribose-5-Phosphate Biosynthesis in Methanocaldococcus jannaschii Occurs in the Absence of a Pentose-Phosphate Pathway". Journal of Bacteriology 187, n. 21 (1 novembre 2005): 7382–89. http://dx.doi.org/10.1128/jb.187.21.7382-7389.2005.
Testo completoAbstract (sommario):
ABSTRACT Recent work has raised a question as to the involvement of erythrose-4-phosphate, a product of the pentose phosphate pathway, in the metabolism of the methanogenic archaea (R. H. White, Biochemistry 43:7618-7627, 2004). To address the possible absence of erythrose-4-phosphate in Methanocaldococcus jannaschii, we have assayed cell extracts of this methanogen for the presence of this and other intermediates in the pentose phosphate pathway and have determined and compared the labeling patterns of sugar phosphates derived metabolically from [6,6-2H2]- and [U-13C]-labeled glucose-6-phosphate incubated with cell extracts. The results of this work have established the absence of pentose phosphate pathway intermediates erythrose-4-phosphate, xylose-5-phosphate, and sedoheptulose-7-phosphate in these cells and the presence of d-arabino-3-hexulose-6-phosphate, an intermediate in the ribulose monophosphate pathway. The labeling of the d-ara-bino-3-hexulose-6-phosphate, as well as the other sugar-Ps, indicates that this hexose-6-phosphate was the precursor to ribulose-5-phosphate that in turn was converted into ribose-5-phosphate by ribose-5-phosphate isomerase. Additional work has demonstrated that ribulose-5-phosphate is derived by the loss of formaldehyde from d-arabino-3-hexulose-6-phosphate, catalyzed by the protein product of the MJ1447 gene.
48
Guo, Jin Ling, Da Chun Gong, Zhi Jun Li e Zhou Zheng. "Construction of Yeast Strain Capable of Co-Fermenting Pentose and Hexose by Protoplast Fusion". Advanced Materials Research 781-784 (settembre 2013): 847–51. http://dx.doi.org/10.4028/www.scientific.net/amr.781-784.847.
Testo completoAbstract (sommario):
Saccharomyces cerevisiae R40 and Pachysolen tannophilus P01 were used as the parental strain to construct an engineering strain capable of co-fermenting pentose and hexose by protoplast fusion. A fusant F202 was obtained through inactivating parental protoplasts, screening with YPX solid medium and high glucose liquid medium, ethanol production capacity detecting and identification with PCR-SSR technique. Subsequently, the fermentation performance and genetic stability of F202 was studied. The maximum ethanol production capacity from glucose was 1.47 ml/100 ml with a sugar and alcohol conversion rate 47% which was 11% higher than the parental strain P01. By fermenting xylose the ethanol concentration could achieve to 0.58 ml/100 ml with a sugar and alcohol conversion rate 12%. An ethanol concentration of 1.2 ml/100 ml was obtained by fermenting the mixture of xylose and glucose (mass ratio 1:2). Moreover, no decrease in ethanol yield after 8 generations propagation suggested fustant 202 possessed good genetic stability.
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Plumed-Ferrer, Carme, Kaisa M. Koistinen, Tiina L. Tolonen, Satu J. Lehesranta, Sirpa O. Kärenlampi, Elina Mäkimattila, Vesa Joutsjoki, Vesa Virtanen e Atte von Wright. "Comparative Study of Sugar Fermentation and Protein Expression Patterns of Two Lactobacillus plantarum Strains Grown in Three Different Media". Applied and Environmental Microbiology 74, n. 17 (20 giugno 2008): 5349–58. http://dx.doi.org/10.1128/aem.00324-08.
Testo completoAbstract (sommario):
ABSTRACT A comparative study of two strains of Lactobacillus plantarum (REB1 and MLBPL1) grown in commercial medium (MRS broth), cucumber juice, and liquid pig feed was performed to explore changes to the metabolic pathways of these bacteria, using a proteomics approach (two-dimensional electrophoresis and liquid chromatography-tandem mass spectrometry) combined with analyses of fermentable sugars and fermentation end products. The protein expression showed that even with an excess of glucose in all media, both strains could metabolize different carbohydrates simultaneously and that hexoses could also be used via a phosphoketolase pathway with preferential expression in liquid feed. Sugar analyses showed that the fermentation of sugars was homolactic for all media, with some heterolactic activity in liquid feed, as shown by the production of acetate. Cucumber juice (the medium with the highest glucose content) showed the lowest hexose consumption (10%), followed by liquid feed (33%) and MRS broth (50%). However, bacterial growth was significantly higher in cucumber juice and liquid feed than in MRS broth. This discrepancy was due to the growth benefit obtained from the utilization of the malate present in cucumber juice and liquid feed. Despite different growth conditions, the synthesis of essential cellular components and the stress response of the bacteria were unaffected. This study has improved our understanding of the mechanisms involved in the growth performance of an appropriate lactic acid bacterium strain to be used for food and feed fermentation, information that is of crucial importance to obtain a high-quality fermented product.
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Aristilde, Ludmilla, Ian A. Lewis, Junyoung O. Park e Joshua D. Rabinowitz. "Hierarchy in Pentose Sugar Metabolism in Clostridium acetobutylicum". Applied and Environmental Microbiology 81, n. 4 (19 dicembre 2014): 1452–62. http://dx.doi.org/10.1128/aem.03199-14.
Testo completoAbstract (sommario):
ABSTRACTBacterial metabolism of polysaccharides from plant detritus into acids and solvents is an essential component of the terrestrial carbon cycle. Understanding the underlying metabolic pathways can also contribute to improved production of biofuels. Using a metabolomics approach involving liquid chromatography-mass spectrometry, we investigated the metabolism of mixtures of the cellulosic hexose sugar (glucose) and hemicellulosic pentose sugars (xylose and arabinose) in the anaerobic soil bacteriumClostridium acetobutylicum. Simultaneous feeding of stable isotope-labeled glucose and unlabeled xylose or arabinose revealed that, as expected, glucose was preferentially used as the carbon source. Assimilated pentose sugars accumulated in pentose phosphate pathway (PPP) intermediates with minimal flux into glycolysis. Simultaneous feeding of xylose and arabinose revealed an unexpected hierarchy among the pentose sugars, with arabinose utilized preferentially over xylose. The phosphoketolase pathway (PKP) provides an alternative route of pentose catabolism inC. acetobutylicumthat directly converts xylulose-5-phosphate into acetyl-phosphate and glyceraldehyde-3-phosphate, bypassing most of the PPP. When feeding the mixture of pentose sugars, the labeling patterns of lower glycolytic intermediates indicated more flux through the PKP than through the PPP and upper glycolysis, and this was confirmed by quantitative flux modeling. Consistent with direct acetyl-phosphate production from the PKP, growth on the pentose mixture resulted in enhanced acetate excretion. Taken collectively, these findings reveal two hierarchies in clostridial pentose metabolism: xylose is subordinate to arabinose, and the PPP is used less than the PKP.