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The Global ETD Search service is a free service for researchers
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Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
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Showing 91 to 100 of 101 (0.025 seconds)| 91 |
Purification and characterisation of novel recombinant β-glucosidases from aspergillus with application in biofuel productionAuta, Richard January 2015 (has links)
β-glucosidases are important components of the cellulase enzyme system in which they not only hydrolyse cellobiose to glucose, but also remove the feedback inhibition effects of cellobiose on exoglucanase and endoglucanase thereby increasing the rate of cellulose degradation to fermentable sugars. A total of 166 proteins were identified as β-glucosidases after manual BLASTp search on the Aspergillus comparative database from eight species. Evidence for Horizontal Gene Transfer (HGT) of bacterial origin of some β-glucosidase genes was provided by their lack of introns, absence of some fungal specific amino acid insertions in their sequences and unusual positions in phylogenetic trees showing similarities to bacterial proteins. A rapid plate assay based on Congo red methods was developed to study the optimum parameters such as pH and temperature for growth of strains and activities of the enzymes produced. Bacterial cellulose (BC) was produced by Gluconacetobacter xylinus. For the first time a fully detailed characterization by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), Differential scanning calorimeter (DSC), Thermogravimetric analysis (TGA) and 13Carbon Solid State Nuclear Magnetic Resonance (SSNMR) of pure BC before and after treatment with a commercially available Aspergillus cellulase enzyme was demonstrated. Two encoding sequences for novel Aspergillus nidulans hydrophobin genes ANID_05290.1 and ANID_07327 that do not fall into either the class I or class II category of hydrophobins were successfully cloned. Two encoding sequences for a novel β-glucosidase gene from an Aspergillus niger strain from Nigeria were amplified and cloned from genomic DNA using PCR. Aspergillus nidulans β-glucosidases (AN2227 and AN1804) expressed in Pichia were purified to homogeneity by using ammonium sulphate precipitation and DEAE-Sephadex A-50 chromatography. Both enzymes had a remarkably broad pH and temperature profile. Further experiments on the development of a technology for lignocellulose degradation based on co-production of β-glucosidase with hydrophobin for biofuel production are suggested.
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Evaluation of the antioxidant and anti-diabesity potential of cyclopia maculata using in vitro non-cell based screening modelsMatrose, Albertina Neliswa January 2014 (has links)
Masters of Science / The aim of this study was therefore to evaluate the antioxidant and anti-diabesity potential of a hot water extract of C. maculata in non-cell based assays and correlate the activities with phenolic composition. Total antioxidant capacity (TAC) was assessed in terms of free radical scavenging and iron reducing ability. The DPPH, ABTS, ORAC and FRAP assays were employed. Anti-diabesity potential was assessed in terms of the inhibition of the digestive enzymes, α-glucosidase and pancreatic lipase
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Antioxidant Response Mechanism in Apples during Post-Harvest Storage and Implications for Human Health BenefitsAdyanthaya, Ishan 01 January 2007 (has links) (PDF)
The biochemical factors affecting post-harvest preservation in apples indicated that well-preserved varieties of apples had increased superoxide dismutase (SOD) activity initially and the activity declined during later storage as apples deteriorated. The SOD link to better preservation correlated with higher phenolic content and free-radical scavenging linked antioxidant activity. Well-preserved varieties were able to maintain a more stable pentose phosphate pathway (PPP) (measured by the activity of glucose-6-phosphate dehydrogenase, G6PDH) throughout the storage period. Proline content increased in all varieties with an increase in proline dehydrogenase (PDH) activity in the initial period indicating proline catabolism supporting potential ATP synthesis. During later storage succinate dehydrogenase (SDH) activity increased while PDH activity declined indicating a shift to tricarboxylic acid cycle and likely NADH generation for ATP synthesis. This shift coupled with the declining SOD activity coincides with rapid deterioration. The guaiacol peroxidase activity (GPX) activity generally declined in late stages indicating post-harvest deterioration. Increasing number of studies have shown that regular intake of fruits and vegetables have clear links to reduced risk of chronic diseases like diabetes and cardiovascular disease. The beneficial effects in many cases have been attributed to the phenolic and antioxidant content of the fruits and vegetables. Apples are a major source of fiber and contain good dietary phenolics with antioxidant function. Previous epidemiological studies have indicated that intake of apples reduces the risk of developing Type II diabetes. Our studies indicate that this reduced risk is potentially due to modulation of postprandial glucose increase by phenolics present in apples via inhibition of a-glucosidase. Phenolic content was evaluated during 3 months of post-harvest storage of four varieties of apples and results indicated positive linkage to enhanced post-harvest preservation and a-glucosidase inhibition. These in vitro results along with existing epidemiological studies provide strong biochemical rationale for further animal or human clinical studies.
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Isolation of Anthocyanin Mixtures from Fruits and Vegetables and Evaluation of Their Stability, Availability and Biotransformation in The Gastrointestinal TractHe, Jian 01 October 2008 (has links)
No description available.
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Hydrolyse de la cellulose par enzymes immobiliséesRoche, Brigitte 18 December 1984 (has links) (PDF)
Depuis longtemps, le bois est utilisé comme combustible, matériau de construction et dans la fabrication de pâtes à papier. Actuellement des procédés thermochimiques, biochimiques et microbiologiques permettent une valorisation du bois conduisant à l'obtention d'intermédiaires chimiques directement utilisables dans l'industrie. L'hydrolyse enzymatique de la cellulose est l'une de ces méthodes. Elle conduit à l'obtention du glucose, point de départ de nombreuses synthèses chimiques dans l'industrie chimique. L'immobilisation de l'enzyme sur support insoluble permet une utilisation répétée de l'enzyme. Cette étude met en évidence le comportement de la cellulase immobilisée vis-à-vis de son substrat. La cellulose est rendue amorphe et soluble par un traitement chimique préalable. Ensuite les différents paramètres influençant l'activité de l'enzyme immobilisée sont étudiés afin de déterminer les conditions optimales de fonctionnement d'un tel système
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Vliv biotického stresu na metabolismus sacharidů rostlin tabáku (Nicotiana tabacum L.) / The effect of biotic stress on the metabolism of saccharides in tobacco plants (Nicotiana tabacum L.)Kloudová, Kateřina January 2012 (has links)
Plants have developed a number of ways how to minimise negative influence of the environment. As a consequence of stress action, plants carbohydrate metabolism is quite often influenced, esp. on the level of expression and activities of different enzymes and also several metabolites concentration. One of key enzymes of carbohydrate metabolism is invertase. The aim of this work was to find out, whether the activity of its isoforms (cytoplasmic, vacuolar and extracellular) in tobacco plants is influenced by Potato virus Y (PVY). It was shown, that activity of cytoplasmic invertase was not affected, but the activity of vacuolar and extracellular isoform was enhanced during potyviral infection. Hence, it is likely, that vacuolar and extracellular invertases are related to plant antiviral defence. The effect of PVY on other enzymes of carbohydrate metabolism and several metabolites content was studied. Activity of α-amylase and phosphorylase, starch-degrading enzymes, was strongly enhanced during potyviral infection. That is probably how plant cells get glucose, which is a key source of energy and metabolites for biosynthesis of different compounds. It may also serve as a signal molecule. Activity of other hydrolytic enzymes, β-glucosidase and β-hexosaminidase, was also slightly increased. There was no...
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Impact of yeast present during pre-fermentation cold maceration on Pinot noir wine aromaHall, Harper L. 14 June 2012 (has links)
This research investigated yeast populations and diversity during pre-fermentation cold maceration and alcoholic fermentation of Vitis vinifera L. cv. Pinot noir grapes from a commercial vineyard (Dayton, OR). Fermentations were conducted at the Oregon State University research winery in 100 L tanks while grapes from the same vineyard lot were fermented at a commercial winery. Samples were taken daily during pre-fermentation maceration (9°C) and alcoholic fermentation (27°C) and plated on WL and lysine media to determine Saccharomyces and non-Saccharomyces populations and diversity. Total non-Saccharomyces populations increased from 1 x 10³ cfu/mL to 1 x 10⁵ cfu/mL during pre-fermentation cold maceration and reached a maximum of 1 x 10⁷ cfu/mL during alcoholic fermentation. Thirteen distinct yeast species were tentatively identified based on appearance on WL media and were initially screened for β-glucosidase activity using 4-methyllumbelliferyl-β-D-gluconopyranoside (4-MUG) plates. The identity of the isolates screening positive for β-glucosidase activity was determined by sequence analysis of the D1/D2 domain of the 26S rDNA gene. The five isolates identified were Metschnikowia pulcherrima, Hanseniaspora uvarum, Kluveromyces thermotolerans, and two Saccharomyces cerevisiae isolates. β-glucosidase activity was further characterized and quantified using a liquid media representing grape must conditions (pH 3.5, 20° Brix) at two temperatures (25°C and 8°C). While increasing sugar concentration suppressed the β-glucosidase activity of H. uvarum (-99%), β-glucosidase activity still remained relatively high for M. pulcherrima, S. cerevisiae isolate 1, and S. cerevisiae isolate 2. At 8°C, β-glucosidase activity was reduced for M. pulcherrima compared to activity at 25°C, but activity increased for K. thermotolerans, S. cerevisiae isolate 1, and S. cerevisiae isolate 2.
The yeast isolates possessing β-glucosidase activity were used in fermentations of Vitis vinifera L. cv. Pinot Noir grapes. The grapes were treated with high hydrostatic pressure (HHP) to inactivate naturally occurring yeast and bacteria. All yeast isolates grew during pre-fermentation cold maceration (7 days at 9°C) and populations increased 3 to 4 logs. Following pre-fermentation cold maceration, all ferments were warmed to 27°C and inoculated with S. cerevisiae RC212. Alcoholic fermentations were all complete within eight days and after pressing wines were analyzed for volatile aroma compounds by SPME-GC-MS. The presence of different yeast isolates during pre-fermentation cold maceration resulted in wines with unique aroma profiles. Ethyl ester concentrations were highest in the wine that did not undergo a pre-fermentation cold maceration, while concentrations of branch-chained esters were higher in the treatments with yeast present during pre-fermentation cold maceration. Pre-fermentation cold maceration with yeast isolates demonstrating β-glucosidase did not affect the concentration of β-damascenone or β-ionone. Wines that had undergone pre-fermentation cold maceration with S. cerevisiae isolate 1, S. cerevisiae isolate 2, and a combination of all isolates resulted in over twice the concentration of β-citronellol over wines that did not undergo a pre-fermentation cold maceration. / Graduation date: 2013
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Activity and kinetics of microbial extracellular enzymes in organic-poor sands of a south Texas estuarySouza, Afonso Cesar Rezende de, 1968- 22 March 2011 (has links)
The respective kinetics of bacterial leucine aminopeptidase and [beta]-glucosidase activities were investigated to improve understanding of factors controlling activity and hydrolytic capacity in estuarine organic-poor sands. Depth distributions of enzyme activity and bulk organic matter content were determined in sediments of Aransas Bay and Copano Bay Texas, to investigate enzyme dynamics as related to the geochemical properties of the sediment. Vertical profiles of activity in sediment showed that the enzymes were more active at the surface and that the potential hydrolysis rate of leucine aminopeptidase was higher than that of [beta]-glucosidase. Vertical patterns of enzyme activity correlated (weakly) with variations in sediment organic matter (TOC, TN, and carbohydrates) content. Enrichments of sediment samples with monomeric organic compounds and inorganic nutrients did not affect leucine aminopeptidase and [beta]-glucosidase activities in short- and long-term incubations. Enzyme activity was independent of nutrient availability and suggested that microbial communities were not nutrient-limited. Time-course assays of bacterial hydrolysis of TOC, TN, and carbohydrates provided information about how substrate limitation may affect enzyme activity. Positive correlations between bulk TOC and TN content and enzyme activity indicated enzyme dependence on polymeric substrate content. Induction of enzyme activity after sediment enrichments with specific labile compounds confirmed the importance of available organic substrate to enzyme hydrolysis efficiency. A kinetic approach established the occurrence of enzyme inhibition and its effects on enzyme hydrolytic capacity. The addition of a specific-enzyme substrate to sediment samples modified enzyme parameters and indicated that a substrate-reversible type of inhibitor could reduce enzyme hydrolytic capacity. The addition of polyphenol, as a natural inhibitor of enzyme activity, to the sediment resulted in a concomitant reduction of leucine aminopeptidase activity and ammonium regeneration rate, and thus demonstrated a close coupling between enzyme activity and sediment ammonium regeneration. These research results demonstrate the dynamic nature of the hydrolytic enzymes, provide information about the mechanisms of induction and inhibition of activity, and demonstrate some implications of reducing the hydrolytic capacity to organic matter decomposition and nutrient regeneration rates. / text
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Successful Treatment of Respiratory Insufficiency Due to Adult Acid Maltase Deficiency With Noninvasive Positive Pressure VentilationPuruckherr, Michael, Pooyan, Payam, Girish, Mirle R., Byrd, Ryland P., Roy, Thomas M. 01 July 2004 (has links)
Acid maltase deficiency (AMD) is a rare autosomal recessive genetic disorder that results in an accumulation of glycogen in the lysosomal storage vacuoles. It is classified as a glycogen storage disease (type II) and is also known as Pompe's disease. The prognosis of the patient with AMD is poor and the main cause of death is respiratory failure. We report a female patient whose respiratory insufficiency was documented to occur most severely during rapid eye movement sleep and who benefited clinically from the institution of nocturnal noninvasive bilevel positive airway pressure.
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Structural Investigation of Processing α-Glucosidase I from Saccharomyces cerevisiaeBarker, Megan 20 August 2012 (has links)
N-glycosylation is the most common eukaryotic post-translational modification, impacting on protein stability, folding, and protein-protein interactions. More broadly, N-glycans play biological roles in reaction kinetics modulation, intracellular protein trafficking, and cell-cell communications.
The machinery responsible for the initial stages of N-glycan assembly and processing is found on the membrane of the endoplasmic reticulum. Following N-glycan transfer to a nascent glycoprotein, the enzyme Processing α-Glucosidase I (GluI) catalyzes the selective removal of the terminal glucose residue. GluI is a highly substrate-specific enzyme, requiring a minimum glucotriose for catalysis; this glycan is uniquely found in biology in this pathway. The structural basis of the high substrate selectivity and the details of the mechanism of hydrolysis of this reaction have not been characterized. Understanding the structural foundation of this unique relationship forms the major aim of this work.
To approach this goal, the S. cerevisiae homolog soluble protein, Cwht1p, was investigated. Cwht1p was expressed and purified in the methyltrophic yeast P. pastoris, improving protein yield to be sufficient for crystallization screens. From Cwht1p crystals, the structure was solved using mercury SAD phasing at a resolution of 2 Å, and two catalytic residues were proposed based upon structural similarity with characterized enzymes. Subsequently, computational methods using a glucotriose ligand were applied to predict the mode of substrate binding. From these results, a proposed model of substrate binding has been formulated, which may be conserved in eukaryotic GluI homologs.
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