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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    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.
101

Development of subunit vaccines against porcine reproductive and respiratory syndrome virus (PRRSV)

Hu, Jianzhong 14 September 2012 (has links)
Since emerging in Europe and the US, PRRS has spread globally and become the most significant infectious disease currently devastating the swine industry. In the US alone, the economic losses caused by this disease amount to more than 560 million US dollars every year. Modified-live PRRSV vaccines (MLV) are the most effective option currently available for the control of the disease. MLVs can confer solid protection against homologous re-infection and have significant effects in reducing viral shedding. But the vaccine efficacy varies upon heterologous challenge. None of the current vaccines are able to completely prevent respiratory infection, transplacental transmission, as well as pig-to-pig transmission of the virus. More importantly, the intrinsic risk of MLV vaccine to revert to virulent virus under farm conditions poses a great safety concern. The unsatisfactory efficacy and safety of current PRRSV vaccines drives the continuous efforts of developing a new generation of vaccines. The strategy we focus on for novel PRRSV vaccine development is subunit vaccine. The reasons for choosing this strategy are: 1) subunit vaccines only contain the immunogenic fragments of a pathogen. Administration of such pathogen fragments eliminates the risk of pathogens reverting back to their virulent form as in the case of modified live vaccines. 2) Subunit vaccines have advantages in terms of vaccine production since a well-defined pathogen fragment can more easily be produced consistently. To achieve of our goal of developing safe and efficacious subunit vaccines against PRRSV, three projects were completed. First, a scalable process for purification of PRRSV particles from cell culture was developed. This process produced purified viral particles for ELISA and cell-based assays used in vaccine development. Second, a plant-made oral subunit vaccine against PRRSV was developed. Administration of the plant-made vaccine, the vaccinated animals produced virus-specific serum and intestine mucosal antibodies with neutralization activity, as well as cellular immune responses with a preference of virus-specific IFN-γ production. Since neutralization antibodies and virus-specific IFN-γ response are the crucial factors contributing to protection against PRRSV infection, the plant-made oral subunit vaccine strategy is an attractive strategy for developing a new generation of the vaccine to control PRRS disease. Third, a chimeric protein consisting of the ectodomains of viral M and GP5 proteins was expressed and purified. The protein product showed a single band on a silver-stained gel and contained an endotoxin level of less than 10 EU/mg protein. In addition, the purified protein showed expected bioactivities. It was antigenic, could bind to a cellular receptor for the virus (heparan sulfate), and could block virus infection of susceptible cells. Therefore, the chimeric protein is a promising subunit vaccine candidate against PRRSV. / Ph. D.
102

Microfluidic platforms for Transcriptomics and Epigenomics

Sarma, Mimosa 18 June 2019 (has links)
A cell, the building block of all life, stores a plethora of information in its genome, epigenome, and transcriptome which needs to be analyzed via various Omic studies. The heterogeneity in a seemingly similar group of cells is an important factor to consider and it could lead us to better understand processes such as cancer development and resistance to treatment, fetal development, and immune response. There is an ever growing demand to be able to develop more sensitive, accurate and robust ways to study Omic information and to analyze subtle biological variation between samples even with limited starting material obtained from a single cell. Microfluidics has opened up new and exciting possibilities that have revolutionized how we study and manipulate the contents of the cell like the DNA, RNA, proteins, etc. Microfluidics in conjunction with Next Gen Sequencing has provided ground-breaking capabilities for handling small sample volumes and has also provided scope for automation and multiplexing. In this thesis, we discuss a number of platforms for developing low-input or single cell Omic technologies. The first part talks about the development of a novel microfluidic platform to carry out single-cell RNA-sequencing in a one-pot method with a diffusion-based reagent swapping scheme. This platform helps to overcome the limitations of conventional microfluidic RNA seq methods reported in literature that use complicated multiple-chambered devices. It also provides good quality data that is comparable to state-of-the-art scRNA-seq methods while implementing a simpler device design that permits multiplexing. The second part talks about studying the transcriptome of innate leukocytes treated with varying levels of LPS and using RNA-seq to observe how innate immune cells undergo epigenetic reprogramming to develop phenotypes of memory cells. The third part discusses a low-cost alternative to produce tn5 enzyme which low-cost NGS studies. And finally, we discuss a microfluidic approach to carrying out low-input epigenomic studies for studying transcription factors. Today, single-cell or low-input Omic studies are rapidly moving into the clinical setting to enable studies of patient samples for personalized medicine. Our approaches and platforms will no doubt be important for transcriptomic and epigenomic studies of scarce cell samples under such settings. / Doctor of Philosophy / This is the era of personalized medicine which means that we are no longer looking at one-size-fits-all therapies. We are rather focused on finding therapies that are tailormade to every individual’s personal needs. This has become more and more essential in the context of serious diseases like cancer where therapies have a lot of side-effects. To provide tailor-made therapy to patients, it is important to know how each patient is different from another. This difference can be found from studying how the individual is unique or different at the cellular level i.e. by looking into the contents of the cell like DNA, RNA, and chromatin. In this thesis, we discussed a number of projects which we can contribute to advancement in this field of personalized medicine. Our first project, MID-RNA-seq offers a new platform for studying the information contained in the RNA of a single cell. This platform has enough potential to be scaled up and automated into an excellent platform for studying the RNA of rare or limited patient samples. The second project discussed in this thesis involves studying the RNA of innate immune cells which defend our bodies against pathogens. The RNA data that we have unearthed in this project provides an immense scope for understanding innate immunity. This data provides our biologist collaborators the scope to test various pathways in innate immune cells and their roles in innate immune modulation. Our third project discusses a method to produce an enzyme called ‘Tn5’ which is necessary for studying the sequence of DNA. This enzyme which is commercially available has a very high cost associated with it but because we produced it in the lab, we were able to greatly reduce costs. The fourth project discussed involves the study of chromatin structure in cells and enables us to understand how our lifestyle choices change the expression or repression of genes in the cell, a study called epigenetics. The findings of this study would enable us to study epigenomic profiles from limited patient samples. Overall, our projects have enabled us to understand the information from cells especially when we have limited cell numbers. Once we have all this information we can compare how each patient is different from others. The future brings us closer to putting this into clinical practice and assigning different therapies to patients based on such data.
103

Separation of Recombinant β-Glucuronidase from Transgenic Tobacco by Aqueous Two-Phase Extraction

Ross, Kristin Coby 28 July 2008 (has links)
Biopharmaceutical manufacturing is a rigorous and expensive process. Due to the medicinal nature of the product, a high purity level is required and several expensive purification steps must be utilized. Cost-effective production and purification is essential for any biopharmaceutical product to be successful and development of the fastest, most economical, and highest-yielding purification scheme is a constant engineering challenge. Commercial-scale purification schemes currently revolve around the use of multiple chromatography steps for the purification of biopharmaceutical products. Chromatography has many shortcomings including high cost, limited throughput, and complex scale up. The goal of this research was to develop an alternative, non-chromatography purification step for the separation of an acidic model protein, recombinant β-glucuronidase (rGUS), from transgenic tobacco with high yield and purity. Aqueous two-phase extraction (ATPE) is a powerful technique for separation and purification of proteins, and has the potential to replace an expensive chromatography step for the initial purification of recombinant proteins. ATPE enables high levels of target protein recovery and concentration while removing large amounts of impurities from the initial extract. Fractional factorial designs and response surface methodology were used to determine an optimized aqueous two-phase system for the purification of rGUS from transgenic tobacco. In a 13.4 % (w/w) PEG/18% (w/w) potassium phosphate system, 74% of the rGUS was recovered in the top PEG-rich phase while 90% of the native tobacco proteins were removed in the interphase and the bottom phase. A purification factor of about 20 was achieved in this process. / Master of Science
104

Methods to study TCDD-inducible poly-ADP-ribose polymerase (TIPARP) mono-ADP-ribosyltransferase activity

11 August 2018 (has links)
No / TCDD-inducible poly-ADP-ribose polymerase (TIPARP; also known as PARP7 and ARTD14) is a mono-ADP- ribosyltransferase that has emerged as an important regulator of innate immunity, stem cell pluripotency, and transcription factor regulation. Characterizing TIPARP’s catalytic activity and identifying its target proteins are critical to understanding its cellular function. Here we describe methods that we use to characterize TIPARP catalytic activity and its mono-ADP-ribosylation of its target proteins.
105

Rekombinantní expresse chloridového kanálu z E. coli a jeho strukturní charakterizace / Recombinant expression of chloride channel from E. coliand its structure characterization

Hausner, Jiří January 2014 (has links)
Chloride channel family has been shown to play a significant role in physiological homeostasis processes. The function mechanism of these proteins has not yet been clearly understood. Their deficiency or mutation causes serious human illnesses. Our understanding of the chloride channels' transporting mechanisms can lead to better treatment of these illnesses. As mammalian chloride channels are difficult to prepare in laboratory, the experiments are usually done on homologous chloride channels from prokaryotic organisms. The structures of prokaryotic chloride channels have been solved and moreover they are produced with high yields. Most experiments currently use protein crystallography and provide a static picture of the system. This thesis is focused on the study of structural changes of an E. coli chloride channel using hydrogen/deuterium exchange. This method enables us to monitor dynamic conformation changes dependent on pH and exchanged ions. The measurements were done for the protonated (pH 4.5) and deprotonated state (pH 7.5) and/or in the presence of various anions: Cl− , SCN− , I− , F− , TAR. (tartaric anion). The obtained results justified the theories explaining the function of chloride channel as Cl− /H+ antiporter and provided new findings. Subject words biochemistry, protein...
106

Štěpení substrátů isoformami savčího Diceru / Substrate cleavage by mammalian Dicer isoforms

Kubíková, Jana January 2016 (has links)
Host organisms evolved antiviral responses, which can recognize the viral infection and deal with it. One of the frequent signs of viral infection in a cell is appearance of double-stranded RNA (dsRNA). One of the pathways responding to dsRNA is RNA interference (RNAi), which functions as the key antiviral defence system in invertebrates and plants. Mammals, however, utilize for antiviral defence a different dsRNA-sensing pathway called the interferon response. RNAi functions only in mammalian oocytes and early embryonal stages although its enzymatic machinery is present in all somatic cells, where it is employed in the microRNA pathway. A previous study indicated that the functionality of RNAi in mouse oocytes functions due to an oocyte-specific isoform of protein Dicer (DicerO ), which is truncated at the N-terminus. In my thesis, I aimed to assess whether DicerO processes RNAi substrates more efficiently in vitro than the full-length Dicer (DicerS ), which is found in somatic cells. Therefore, I developed Dicer purification protocol for obtaining both recombinant mouse Dicer isoforms of high purity. I examined their activity in a non-radioactive cleavage assay using RNA substrates with structural features characteristic of RNAi substrates. My results suggest that recombinant DicerO and DicerS do not...
107

Remoção de endotoxina presente em meio fermentado contendo biomoléculas utilizando sistemas micelares de duas fases aquosas / Endotoxin removal from fermentation broth containing biomolecules using two-phase micellar system

Lopes, André Moreni 20 August 2010 (has links)
Foi investigada a utilização de Sistema Micelar de Duas Fases Aquosas (SMDFA) para remoção de lipolissacarídeos (LPS) de preparações contendo proteínas recombinantes de interesse farmacêutico, como a proteína verde fluorescente (GFPuv). Os SMDFA são constituídos por soluções de tensoativos contendo micelas e oferecem ambientes hidrofóbico e hidrofílico, que possibilitam seletividade na partição de biomoléculas de acordo com sua hidrofobicidade, permitindo a remoção de LPS contaminante. Neste trabalho, foi realizada a implementação do método para a quantificação de LPS em amostras contaminadas e a obtenção de LPS e GFPuv puros a partir de cultivo de E. coli recombinante. Além disso, foi estudada a influência do Triton X-114 na metodologia de quantificação de LPS, e a adição de MgSO4, CaCl2, KI e (NH4)2SO4 na partição de GFPuv e LPS puros em SMDFA. E ainda, realizou-se um planejamento experimental (22) para avaliar os maiores KGFPuv e %RECGFPuv. O homogeneizado celular de E. coli foi testado nas melhores condições obtidas com o planejamento experimental. E finalmente, o processo por cromatografia de afinidade por íons metálicos (IMAC) foi empregado para investigar a adsorção de LPS em matriz IDA-Ca2+. Conforme os resultados obtidos, o TX-114 causou elevada interferência no método cinético cromogênico, em função da similaridade desta molécula com os LPS. Os LPS apresentaram partição preferencial para a fase concentrada em micelas, com altos valores de remoção, %REMLPS>98,0%. Ao contrário, a GFPuv foi recuperada preferencialmente na fase diluída, na qual existe maior volume disponível, resultando em valores de KGFPuv>1. A adição de sais ocasionou diminuição nos valores KGFPuv, provavelmente por causa da carga negativa que GFPuv adquiriu nas condições avaliadas. Os resultados do planejamento experimental mostraram que a melhor condição de partição obtida foi na região do ponto central, 4,0% (p/p) a 60,0°C, com KGFPuv>10. O processo por IMAC apresentou as maiores capacidades de adsorção de LPS-IDA-Ca+2 nas condições de menor pH e maior força iônica 4,0 e 1,0 mol/L, respectivamente. O processo de purificação por SMDFA empregado para a remoção de LPS contaminante presente em meio fermentado contendo GFPuv, demonstrou ser eficiente em recuperar a biomolécula-alvo na fase diluída e separar o principal contaminante na fase rica em micelas. Portanto, pode ser empregado como primeira etapa para a remoção de altas concentrações de LPS na purificação de proteínas hidrofílicas como a GFPuv. / The Aqueous Two-Phase Micellar System (ATPMS) was investigated for endotoxin (LPS) removal from preparations containing recombinant proteins of pharmaceutical interest, such as the green fluorescent protein (GFPuv). These systems usually consist of micellar surfactants solutions and offer both hydrophobic and hydrophilic environments, providing selectivity to the biomolecules partitioning according to its hydrophobicity. In this work, the implementation of the method for LPS quantification in contaminated samples was accomplished, as well as the obtaining of pure LPS and GFPuv from recombinant E. coli. Furthermore, the influence of Triton X-114 in the methodology for LPS quantification was studied, as the addition of MgSO4, CaCl2, KI, and (NH4)2SO4 into the partition of pure GFPuv and LPS in ATPMS. In addition, a statistical design (22) was carried out to evaluate the highest KGFPuv and %RECGFPuv. The E. coli cell lysate was tested under optimum conditions obtained with the statistical design. And, finally, the process by ionmetal affinity chromatography (IMAC) was used to investigate the adsorption of LPS in IDA-Ca2+ matrix. The results showed that the TX-114 caused high interference in the kinetic chromogenic method, according to the similarity of this molecule to LPS. The LPS showed preferential partitioning to the micellerich phase, with high values of removal, %REMLPS>98.0%. In the other hand, the GFPuv was preferentially recovered in the micelle-poor phase, in which there is greater volume available resulting in values of KGFPuv>1. The addition of salts caused a reduction in the values KGFPuv, probably because of the negative charge that the GFPuv acquired at the conditions evaluated. The results of the statistical design showed that the best partitioning condition obtained was in the central point region, 4.0% (wt/wt) at 60.0°C, with KGFPuv>10. The process by IMAC showed the highest adsorption of LPS-IDA-Ca+2 capacities at the conditions of lower pH and higher ionic strength 4.0 and 1.0 mol/L, respectively. The purification process for the LPS contaminant removal from E. coli fermentation containing GFPuv by ATPMS proved to be efficient in the recovering of target biomolecule in the micelle-poor phase, and separating the main contaminant in the micelle-rich phase. Furthermore, this system can be exploited as the first step for removal of higher LPS concentrations from hydrophilics protein purification.
108

Remoção de endotoxina presente em meio fermentado contendo biomoléculas utilizando sistemas micelares de duas fases aquosas / Endotoxin removal from fermentation broth containing biomolecules using two-phase micellar system

André Moreni Lopes 20 August 2010 (has links)
Foi investigada a utilização de Sistema Micelar de Duas Fases Aquosas (SMDFA) para remoção de lipolissacarídeos (LPS) de preparações contendo proteínas recombinantes de interesse farmacêutico, como a proteína verde fluorescente (GFPuv). Os SMDFA são constituídos por soluções de tensoativos contendo micelas e oferecem ambientes hidrofóbico e hidrofílico, que possibilitam seletividade na partição de biomoléculas de acordo com sua hidrofobicidade, permitindo a remoção de LPS contaminante. Neste trabalho, foi realizada a implementação do método para a quantificação de LPS em amostras contaminadas e a obtenção de LPS e GFPuv puros a partir de cultivo de E. coli recombinante. Além disso, foi estudada a influência do Triton X-114 na metodologia de quantificação de LPS, e a adição de MgSO4, CaCl2, KI e (NH4)2SO4 na partição de GFPuv e LPS puros em SMDFA. E ainda, realizou-se um planejamento experimental (22) para avaliar os maiores KGFPuv e %RECGFPuv. O homogeneizado celular de E. coli foi testado nas melhores condições obtidas com o planejamento experimental. E finalmente, o processo por cromatografia de afinidade por íons metálicos (IMAC) foi empregado para investigar a adsorção de LPS em matriz IDA-Ca2+. Conforme os resultados obtidos, o TX-114 causou elevada interferência no método cinético cromogênico, em função da similaridade desta molécula com os LPS. Os LPS apresentaram partição preferencial para a fase concentrada em micelas, com altos valores de remoção, %REMLPS>98,0%. Ao contrário, a GFPuv foi recuperada preferencialmente na fase diluída, na qual existe maior volume disponível, resultando em valores de KGFPuv>1. A adição de sais ocasionou diminuição nos valores KGFPuv, provavelmente por causa da carga negativa que GFPuv adquiriu nas condições avaliadas. Os resultados do planejamento experimental mostraram que a melhor condição de partição obtida foi na região do ponto central, 4,0% (p/p) a 60,0°C, com KGFPuv>10. O processo por IMAC apresentou as maiores capacidades de adsorção de LPS-IDA-Ca+2 nas condições de menor pH e maior força iônica 4,0 e 1,0 mol/L, respectivamente. O processo de purificação por SMDFA empregado para a remoção de LPS contaminante presente em meio fermentado contendo GFPuv, demonstrou ser eficiente em recuperar a biomolécula-alvo na fase diluída e separar o principal contaminante na fase rica em micelas. Portanto, pode ser empregado como primeira etapa para a remoção de altas concentrações de LPS na purificação de proteínas hidrofílicas como a GFPuv. / The Aqueous Two-Phase Micellar System (ATPMS) was investigated for endotoxin (LPS) removal from preparations containing recombinant proteins of pharmaceutical interest, such as the green fluorescent protein (GFPuv). These systems usually consist of micellar surfactants solutions and offer both hydrophobic and hydrophilic environments, providing selectivity to the biomolecules partitioning according to its hydrophobicity. In this work, the implementation of the method for LPS quantification in contaminated samples was accomplished, as well as the obtaining of pure LPS and GFPuv from recombinant E. coli. Furthermore, the influence of Triton X-114 in the methodology for LPS quantification was studied, as the addition of MgSO4, CaCl2, KI, and (NH4)2SO4 into the partition of pure GFPuv and LPS in ATPMS. In addition, a statistical design (22) was carried out to evaluate the highest KGFPuv and %RECGFPuv. The E. coli cell lysate was tested under optimum conditions obtained with the statistical design. And, finally, the process by ionmetal affinity chromatography (IMAC) was used to investigate the adsorption of LPS in IDA-Ca2+ matrix. The results showed that the TX-114 caused high interference in the kinetic chromogenic method, according to the similarity of this molecule to LPS. The LPS showed preferential partitioning to the micellerich phase, with high values of removal, %REMLPS>98.0%. In the other hand, the GFPuv was preferentially recovered in the micelle-poor phase, in which there is greater volume available resulting in values of KGFPuv>1. The addition of salts caused a reduction in the values KGFPuv, probably because of the negative charge that the GFPuv acquired at the conditions evaluated. The results of the statistical design showed that the best partitioning condition obtained was in the central point region, 4.0% (wt/wt) at 60.0°C, with KGFPuv>10. The process by IMAC showed the highest adsorption of LPS-IDA-Ca+2 capacities at the conditions of lower pH and higher ionic strength 4.0 and 1.0 mol/L, respectively. The purification process for the LPS contaminant removal from E. coli fermentation containing GFPuv by ATPMS proved to be efficient in the recovering of target biomolecule in the micelle-poor phase, and separating the main contaminant in the micelle-rich phase. Furthermore, this system can be exploited as the first step for removal of higher LPS concentrations from hydrophilics protein purification.
109

Characterization of secondary microbial communities in industrial bioreactors producing high value chemicals

Kindt, Rocky January 2017 (has links)
Microbial communities are key drivers of biogeochemical cycles and several important industrial processes rely on complex, undefined microbial ecosystems for production or conversion of substrates for example in wastewater treatment or anaerobic digestion plants. Despite their significance, such communities are often poorly defined, if at all. This project concerned previously undefined secondary microbial communities (SMCs) from photobioreactors culturing cyanobacterium Arthrospira platensis, known for producing high-value protein-pigment complex C-phycocyanin (C-PC). C-PC has a range of applications in the biochemical/pharmaceutical and food industries. Next-generation sequencing methods were applied to characterize the SMCs sampled over the course of various batch runs. The bioreactor exerted a strong selective pressure on the SMC, initially diverse and dynamic, succeeded by a stable and predictable SMC dominated by a few species. SMC stability and diversity correlated with reactor performance, especially proliferation and instability of the rare-abundance sub-population; dominant species ratios were likely less important. The substantially larger (compared to other species present) A. platensis filaments may represent a dynamic microenvironment in itself, and if so, constitutes a significant parameter when optimizing culture conditions. Denser and carefully pre-acclimated inocula reduce the ecological space available to undesirable taxa (e.g. pathogens) otherwise below detectable/significant limits. This has implications for other processes that rely on mixed cultures and may be a control strategy in manufacturing active pharmaceutical ingredients to cGMP standards. Molecular data was used to obtain several pure isolates which were characterized further. Strategies to optimize performance with respect to SMCs were explored and evaluated. A significant aspect of this CASE project was an industrial placement with Scottish Bioenergy. The placement involved set-up of a production facility and incremental scale-up of cultivation from 2 L to 1000 L reactors; development of a downstream processing protocol covering harvesting, pigment extraction and protein purification, and some formulation/stability testing. A very low-cost method is described for obtaining relatively high-purities of C-PC, broadly considered the most costly part of the entire production process.
110

Caracterização da trealase solúvel de Spodoptera frugiperda (Lepidoptera) / Characterization of the soluble trehalase of Spodoptera frugiperda (Lepidoptera)

Maria Cicera Pereira da Silva 25 February 2003 (has links)
No epitélio do intestino médio de S. frugiperda encontra-se 90% da atividade de trealase solúvel. A trealase solúvel foi purificada até a homogeneidade por uma série de passos cromatográficos. A enzima possui um sítio hidrofóbico adjacente ao sítio ativo. Mudanças conformacionais aparentemente ocorrem quando metil-a-glicosídeo liga-se ao sítio ativo. A trealase solúvel é inibida competitivamente por amigdalina (Ki=0,21 mM), prunasina (Ki=0,92 mM), mandelonitrila (Ki = 1,14 mM), metil-α-glicosídeo (Ki=89 mM), metil-α-manosídeo (Ki=6,2 mM )e salicina (Ki= 19 mM). Florizina é um inibidor acompetitivo hiperbólico da trealase solúvel (Ki=0,087 mM, α =β =0,35) e seu aglicone floretina é um inibidor não competitivo (Ki=0,029 mM). Tris e mandelonitrila ligam-se a regiões diferentes da enzima enquanto mandelonitrila e floretina não podem ligar-se concomitantemente à enzima. Os pKs da enzima livre (pKe) e do complexo enzima substrato (pKes) foram determinados a partir de valores de Km e Vmáx/Km obtidos em vários pHs. Os valores encontrados foram: pKe1=4,47; pKe2=8,0l ; pKes1=4,83; pKes2=7,59. A trealase solúvel não perde a atividade quando incubada com reagentes que modificam grupos sufidrila, thiol e fenol. Com modificador de grupo imidazol, a enzima perde 60% da atividade somente na presença de metil-α-glucosídeo (inibidor competitivo da trealase). Essa modificação é protegida por trealose, indicando a presença de uma Histidina não essencial para catálise. Modificadores de grupo carboxila e guanidino inativam a enzima, com pKs de, respectivamente, 4,87 e 7,84. a similaridade desses pKs com os determinados cineticamente sugere que os resíduos envolvidos em catálise são uma arginina e um asparto ou glutamato. β-glicosídeos tóxicos produzidos por plantas e seus aglicones inibem trealoses presentes em diferentes órgãos de várias ordens de insetos. Essa inibição foi menor em insetos que se alimentam somente de vegetais, provavelmente devido a uma adaptação desses organismos. / The epithelium of S. frugiperda midgut has a trehalase activity that is mainly soluble (90%). The soluble trehalase was purified by several chromatographic steps. The enzyme has an hydrophobic site near the active site. Conformational changes apparently occur in the enzyme when methyl-α-glucoside binds to the active site. Trehalase has a Km=0.37 mM and is a competitively inhibited by methyl-α-glucoside (Ki=89 mM); methyl-α-mannosideo (Ki=6.2 mM); amygdalin (Ki=0.21); prunasin (Ki=0.92 mM); mandelonitrile (Ki=l.14 mM); Tris (Ki=0.55 mM) and salicin (Ki=l9 mM). Phlorizin is an hyperbolic acompetitive inhibitor (α=β=0.35; Ki=0.0087 mM), whereas its aglycon, phloretin, is a non-competitive inhibitor (Ki=0.029 mM). Tris and mandelonitrile bind at the same region in the active site. On the other hand, mandelonitrile and phloretin cannot be bound to the enzyme at the same time. Enzyme pKs (pKe) and enzyme substrate pKs (pKes) were determined from Km and Vmax/Km values obtained at different pHs. The values are: pKe1=4.47; pKe2=8.0l ; pKes1=4.83; pKes2=7.59. Trehalase is not inactivated when incubated with compounds that react with thiol, imidazole or phenol groups. Trealase lose 60% of its activity in the presence of methyl-α-glucoside (acompetitive inhibitor) plus a compound that reacts with imidazole groups. This inactivation is decreased by trehalose, indicating that there is a non-essential histidine in the active site substances that react with carboxyl guanidine groups inactivate the enzyme. The modified groups have pH of respectively, 4.87 and 7.84. The resemblance of these pKs with the one determined from Km and Vmax values suggest that the prototropic groups of the enzyme are in residues of arginine and aspartic acid or glutamic acid. Toxic β-glucosides from plants and their aglycons inhibit trealase from different organs of insects from several orders. This inhibition is lower in herbivorous insects, possibly due to their adaptation in ingesting vegetal tissues.

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