• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 116
  • 18
  • 13
  • 4
  • 4
  • 2
  • 2
  • 2
  • 1
  • Tagged with
  • 211
  • 211
  • 43
  • 40
  • 29
  • 27
  • 25
  • 20
  • 20
  • 18
  • 17
  • 15
  • 13
  • 13
  • 13
  • 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.
91

ISOPRENOID ANALOGS AS CHEMICAL GENETIC TOOLS TO PROVIDE INSIGHTS INTO FARNESYL TRANSFERASE TARGET SELECTION AND CELLULAR ACTIVITY

Troutman, Jerry 01 January 2006 (has links)
Protein farnesylation is an essential post-translational modification required for the function of numerous cellular proteins including the oncoprotein Ras. The farnesyl transferase (FTase) catalyzed reaction is unique because farnesyl diphosphate (FPP), the farnesyl group donor for the reaction, forms a significant portion of a target protein binding site. The major goal of this research was to exploit this unique property of the FTase reaction and determine if changing the structure of the farnesyl donor group would affect FTase protein targeting. A small library of structural analogues of FPP was synthesized. Michelis-Menten steady-state kinetic analyses and competition reactions were used to determine the effect of these structural modifications on FTase targeting. We found that the analogues did affect FTase protein selectivity and that this could be exploited to induce unnatural target selectivity into the enzyme. The second goal of this research was to determine the effect of FPP analogues on the function of FTase target proteins. To test the effect of these analogues we determined whether the unnatural lipid could ablate oncogenic H-Ras biological function in a Xenopus laevis model system. Several analogues were able to disrupt oncogenic H-Ras function while others mimicked the activity of FPP. These results indicated that some of the FPP analogues may act a prenyl group function inhibitors that could lead to an important new class of anti-cancer therapeutics. Another major goal of this research was to use the FPP analogues as unnatural probes for the endogenous cellular activity of FTase target proteins. We developed antibodies to two of the unnatural FPP analogues to study their activity in cell cultureUtilizing these antibodies we found that alcohol prodrugs of the FPP analogues could be incorporated into cellular proteins in an FTase dependent manner. The ability of cell permeant analogues to be incorporated into live cells enhances the chances that such a molecule could be used to modify oncogenic cellular proteins with a prenyl group function inhibitor.
92

Studies of enzyme kinetics and aspects of enzyme structure in vivo using NMR and molecular genetics

Williams, Simon-Peter January 1992 (has links)
A quantitative understanding of metabolic control depends on a knowledge of the enzymes involved. The extrapolation of studies in vitro to the intact cell is controversial because the intracellular environment is relatively poorly characterised, particularly with respect to the interactions between weakly-associated enzymes. There is a clear need to study enzymes directly in the cell, yet there are few suitable techniques. Metabolites have been very successfully studied in cells by the non-invasive technique of nuclear magnetic resonance (NMR). NMR studies of enzymes in the cell have, however, been prevented by difficulties in assigning the resonances from the many proteins within the cell. A method for studying a specific enzyme in the cell has been developed, using Saccharomyces cerevisiae and phosphoglycerate kinase (PGK) as a model system. Using an inducible expression system, PGK was synthesised in the cell without significant synthesis of other proteins. With 5-fluorotryptophan in the growth medium, fluorine-labelled PGK was formed in situ. Fluorine is an excellent label for NMR since it is absent from most cells and has a high receptivity to NMR detection. <sup>19</sup> F NMR was used to study PGK in the intact cell. Comparisons with measurements in vitro showed that PGK was exposed to only a small fraction of the total intracellular [ADP], implying some form of compartmentalisation. The NMR relaxation properties observed in vivo and in vitro were compared with theoretical predictions. This showed that PGK was not part of a complex in the cell and that the viscosity of the cytoplasm, relative to water, was c. 4 at 30 °C. Fluorine-labelled pyruvate kinase and hexokinase have also been prepared; the spectra of these proteins in vitro are responsive to their ligands, and further work will study these proteins in vivo. NMR techniques were also applied to study the kinetics of PGK in the cell. PGK and GAPDH catalyse an ATP↔P<sub>i</sub> exchange which is near-equilibrium in wild-type cells. <sup>31</sup>P magnetisation transfer experiments in genetically manipulated cells showed that the reaction becomes unidirectional if the PGK activity is reduced by 95 %. Net flux is reduced by less than 30 %. In low-PGK cells, the ATP↔P<sub>i</sub> exchange from oxidative phosphorylation can be isolated from that of glycolysis, facilitating direct measurements of the P:O ratio. In the cells studied, the P:O ratio was 2 to 3.
93

The molecular basis for sulfite oxidation in a bacterial sulfite dehydrogenase from Starkeya novella

Trevor Rapson Unknown Date (has links)
Sulfite oxidising enzymes are found in all forms of life and play an important role in detoxification of sulfite produced through biochemical processes. All known sulfite oxidising enzymes share a common molybdenum active site. The sulfite dehydrogenase (SDH) from the soil bacterium Starkeya novella differs from the vertebrate sulfite oxidases (SO) in that the heme and Mo subunits are tightly associated rather than connected by a flexible hinge. This structural integrity makes SDH an ideal model enzyme for the study of enzymatic sulfite oxidation without the complications of structural changes underlying catalysis. In human sulfite oxidase (HSO) the substitution of a conserved active site amino acid residue, Arg-160 for Gln, results in a lethal disease. A number of independent studies have been carried out in order to understand the effects of this substitution on catalysis in both human (HSO) and chicken sulfite oxidising enzymes (CSO). The focus of this work is the analogous residue in SDH, Arg 55. A number of active site substitutions have been investigated, including SDHR55Q, an analogous substitution to the lethal mutation identified in humans. In addition, the properties of the Arg residue have also been probed using a substitution to a hydrophobic residue, Met (SDHR55M) and a substitution to the positively charged Lys (SDHR55K). A fourth active site substitution, SDHH57A, was also investigated as the crystal structure of this variant indicated that His-57 plays a role in stabilising the position of Arg-55 in SDH. It was of interest to determine the effect of the instability in the position of Arg-55 on the catalytic parameters of the SDHH57A. The kinetic properties of the substituted enzymes were investigated using steady-state assays with cytochrome c as an electron acceptor. When the positive charge was lost in the case of SDHR55M and SDHR55Q, a dramatic increase in the KM (sulfite - app) of 2 – 3 orders of magnitude resulted. This indicates that the positive charge on Arg-55 is important for substrate binding. All the Arg-55 variants studied were found to have lower turnover numbers than the wild type, in particular, SDHR55Q was found to have a reduced kcat (108 s-1 vs 345 s-1 for SDHWT at pH 8). The changes in the Mo centre underlying the altered kinetic properties were investigated in detail using EPR spectroscopy of the intermediate MoV oxidation state in SDHR55Q and SDHH57A. Similar to what has been noted for HSOR160Q, a sulfate blocked form was observed at pH 6 using pulsed EPR experiments, suggesting that this substitution causes an inhibition of the hydrolysis step required to release the reaction product, sulfate. This could be a further reason for the poor catalytic activity of SDHR55Q, in particular, a reason for the low turnover rate of this variant. Unlike what was noted in HSOR160Q, where the substituted enzyme showed a dramatic decrease in rate of intramolecular transfer by three orders of magnitude compared to HSOWT, the rate of electron transfer was found to be 3 times faster in SDHR55Q relative to the wild type enzyme. These results indicate that Arg-55 is not involved in the pathway of electron transfer between the Mo and heme centres, but rather assists with the the docking of the heme group in HSO. As this process is not required in SDH, our results suggest that intramolecular electron transfer (IET) in HSOR160Q decreases because it is crucial for docking of the heme domain. Through potentiometric redox titrations, the effect of the active site amino acid substitutions on both the Mo and Fe redox potentials was investigated. No significant change was determined for the MoVI/V redox potentials, however, the heme potentials for SDHWT and SDHR55K were 40 mV higher than those of the other variants, with the lowest potentials belonging to SDHR55M and SDHH57A. Of further interest was that the MoVI/V couple is significantly lower than the heme couple (175 mV vs 240 mV respectively) in SDHWT. It appears that the positive charge of the Arg is important in regulating the heme redox potentials and could thereby contribute to modulating enzymatic activity. When SDH was immobilised on a modified pyrolytic graphite electrode, stable and high catalytic currents were observed, indicating facile heterogeneous electron transfer between the enzyme and the electrode. This good electron transfer allowed the catalytic properties of SDH and its substituted enzymes to be investigated as a function of potential. A pH dependence ( 59 mV/pH) in the catalytic operating potential was noted for SDHWT and SDHR55K, which appears to follow the pH dependence of the MoVI/V couple. This catalytic potential is pH-independent in the R55M and H57A variants, where the catalytic operating potentials appeared to follow the FeIII/II redox couple. It is proposed that two distinct pathways of electron transfer from the Mo centre to the electrode are likely to exist. The first is direct transfer from the Mo centre to the electrode at lower potential (~ 175 mV) while the second proceeds via the heme group (320 mV). The pathway followed is determined by the oxidation state of the heme group. A slight difference in the electron transfer rates of these two processes was seen, with direct transfer (from Mo) being the faster, which accounts for the unusual peak shape noted in the voltammogram for SDHWT at high sulfite concentrations, where the rate of catalytic activity slows at a higher potentials despite the greater thermodynamic driving force. This work provides new insights into the mechanism of enzymatic sulfite oxidation. Arg-55 has been shown to play an important role in the catalytic functioning of SDH in both substrate affinity and product release. Unlike what has been previously proposed, Arg-55 does not play a part in the pathway of electron transfer, but is rather involved in the regulation of the redox potentials of the metal centres in the enzyme.
94

Structure/function studies on metallo-B-lactamase ImiS from Aeromonas bv. sobria

Sharma, Narayan Prasad. January 2007 (has links)
Thesis (Ph. D.)--Miami University, Dept. of Chemistry and Biochemistry, 2007. / Title from second page of PDF document. Includes bibliographical references.
95

Purificação parcial e caracterização bioquímica de uma isoforma de β-glicosidase do fungo termofílico Myceliophthora thermophila M.7.7 / Partial purification and biochemical characterization of a β-glucosidase isoform from the thermophilic fungus Myceliophthora thermophila M.7.7

Bonfá, Emily Colferai [UNESP] 29 February 2016 (has links)
Submitted by Emily Colferai Bonfá null (miemilymi@hotmail.com) on 2016-03-22T01:17:39Z No. of bitstreams: 1 Mestrado-Emily Finall.pdf: 1593107 bytes, checksum: ce9ebf44b67e4020e069a84d708f2f71 (MD5) / Approved for entry into archive by Ana Paula Grisoto (grisotoana@reitoria.unesp.br) on 2016-03-22T17:56:40Z (GMT) No. of bitstreams: 1 bonfa_ec_me_sjrp.pdf: 1593107 bytes, checksum: ce9ebf44b67e4020e069a84d708f2f71 (MD5) / Made available in DSpace on 2016-03-22T17:56:40Z (GMT). No. of bitstreams: 1 bonfa_ec_me_sjrp.pdf: 1593107 bytes, checksum: ce9ebf44b67e4020e069a84d708f2f71 (MD5) Previous issue date: 2016-02-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / As celulases podem ser utilizadas na bioconversão da fração de celulose de resíduos agro-industriais em açúcares fermentáveis, visando a obtenção de combustíveis renováveis e produtos químicos. As β-glicosidases são cruciais para a total sacarificação da celulose, mas na maioria dos casos elas são fortemente inibidas pelo seu produto, a glicose. Portanto, o conhecimento das cinéticas de hidrólise e as respostas dessa enzima frente a diferentes substratos e produtos pode definir a eficiência de hidrólise e do processo biotecnológico no qual poderia ser incorporada. O presente trabalho teve como objetivo caracterizar a β -glicosidase de 50 kDa (BG50) produzida pelo fungo termofílico Myceliophthora thermophila M.7.7 cultivado em estado sólido, em mistura de bagaço de cana e farelo de trigo (1:1). O zimograma do extrato bruto evidenciou duas isoformas, de aproximadamente 200 e 50 kDa, as quais foram separadas por cromatografia de filtração em gel. A caracterização da BG50 mostrou atividade ótima a 60 ˚C e pH 5,0 quando usado o 4-nitrofenol-β-D-glicopiranosídeo (pNPG), enquanto com celobiose o valor da temperatura e pH ótimo foram de 50 ˚C e pH 4,5, respectivamente. Testes realizados com adição de íons e reagentes mostraram diferenças nos efeitos sobre a atividade da enzima dependendo do substrato, principalmente com a adição de Ditiotreitol (DTT) utilizando celobiose, e inibição completa com Cu2+ e Fe3+ para pNPG e celobiose. Além disso, a enzima não mostrou efeito inibitório quando testada na presença de nove compostos fenólicos, uma característica significativa. Os estudos cinéticos revelaram um perfil de inibição competitiva pela glicose quando utilizado pNPG com valor de KI=1,5 mM e um Km significativamente menor (0,52 mM) pelo pNPG do que pela celobiose (Km=8,50 mM). Os parâmetros termodinâmicos mostraram que a BG50 é bastante estável, destacando seu tempo de meia vida de 855,6 minutos a 60 °C, porém desnatura facilmente acima dessa temperatura. Os resultados enfatizam a importância de investigar potencialidades de β-glicosidases baseadas na celobiose, uma vez que no processo industrial a enzima atuará sobre o substrato natural, além da compreensão da termoestabilidade da enzima. / Cellulases can be used in bioconversion of cellulose from agro-industrial waste into fermentable sugars in order to obtain renewable fuels and chemicals. The β-glucosidases are crucial to the overall saccharification of cellulose, but in most cases, they are strongly inhibited by its product, glucose. Therefore, knowledge of the hydrolysis kinetics of the enzyme and its responses against different substrates and products can set the hydrolysis efficiency and possible incorporation in biotechnological process. This study aimed to characterize the 50 kDa β-glucosidase (BG50) produced by the thermophilic fungus Myceliophthora thermophila M.7.7 grown in solid state, in a mixture of sugarcane bagasse and wheat bran (1:1). The zymogram of the crude extract showed two isoforms of 200 and 50 kDa, which were separated by gel filtration chromatography. The characterization of BG50 showed optimal activity at 60 °C and pH 5.0 when used pNPG, whereas using cellobiose the values of the optimal temperature and pH were 50 °C and pH 4.5, respectively. Tests with addition of reactants and ions showed differences in the effects on enzyme activity depending on the substrate, especially with the addition of dithiothreitol (DTT) utilizing cellobiose, and complete inhibition with Cu2+ and Fe3+ for 4-nitrophenyl-β- D-glucopyranoside (pNPG) and cellobiose. Furthermore, the enzyme showed no inhibitory effect when tested in the presence of nine phenolic compounds, a remarkable characteristic. Kinetic studies showed a profile of competitive inhibition by glucose when using pNPG with Ki = 1.5 mM and Km significantly lower (0.52 mM) with pNPG than using cellobiose (Km = 8.50 mM). The thermodynamic parameters show that BG50 is quite stable, highlighting its half life of 855.6 minutes at 60 ° C, but above this temperature easily denatured. The results emphasize the importance of investigating β-glucosidases’ potential based on cellobiose, since for the industrial processes the enzyme will function with its natural substrate, in addition to understanding the thermal stability of the enzyme.
96

Caracterização funcional e estrutural da nucleotidase SurE de Xyllela fastidiosa / Functional and structural characterization of nucleotidase SurE from Xyllela fastidiosa

Saraiva, Antonio Marcos 14 August 2018 (has links)
Orientador: Anete Pereira de Souza / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-14T21:21:36Z (GMT). No. of bitstreams: 1 Saraiva_AntonioMarcos_D.pdf: 12032714 bytes, checksum: 1262a05ca10735e855fa138a2093d04b (MD5) Previous issue date: 2009 / Resumo: A linhagem 9a5c da bactéria Xylella fastidiosa foi o primeiro fitopatógeno a ter seu genoma completamente sequenciado, o qual gerdu diversas informações sobre seu metabolismo e patogenicidade. Das orfs codificadas por esta bactéria, destaca-se; no presente trabalho, a XF0703, cuja proteína correlata (com 28,3 kDa) possui similaridade com proteínas SurE de várias outras bactérias. Proteínas SurEs são nucleotidases que desfosforilam diversos nucleosideos monofosforilados para seus respectivos nucleosideos. Tal função é de fundamental importância para manter o pool balanceado dos quatro (deoxi)ribonucleosideos para síntese de DNA e RNA, respectivamente. Este trabalho descreve a clonagem da orfXF0703 no vetor pET29a, a expressão da proteína recombinante (XfSurE) em Escheríchia coli BL21(DE3) e a purificação da mesma por cromatografia de afinidade ao níquel. A análise da estrutura secundária foi feita por dicroísmo circular e realizou-se a determinação do estado oligomérico por cromatografia de gel filtração e espalhamento de luz a baixo ângulo (SAXS), os quais revelaram que a proteína é um tetrâmero. Dados de caracterização funcional indicam que a proteína possui maior atividade em pH neutro na presença do íon manganês como cofator, com uma maior afinidade pelo substrato 3'-AMP (K0,5=0,16 mM). Além disso, ensaios cinéticos mostram que a proteína possui um comportamento alostérico com alta cooperatividade positiva (coeficiente de Hill em torno de 2,6) com todos os quatro substratos naturais testados (3'-AMP, 5'-dAMP, 5'-AMP e 5-GMP). Experimentos com a técnica de SAXS permitiram calcular o raio de giro (32,7 ± 0.2 A), distância máxima intramolecular (100 A) e a simetria do envelope da molécula (222). A estrutura de diversas SurEs homólogas já cristalizadas foram superpostas ao envelope obtido, sendo que StSurE (SurE de Salmonella com maior idenjidade de aminoácidos) mostrou ter o melhor ajuste. No entanto, notou-se que havia espaços vazios no envelope de XfSurE e tais espaços podiam ser preenchidos a partir do afastamento das alças responsáveis pela tetramerização e pela rotação dos f dímeros. Estes movimentos (translação e rotação) podem explicar o comportamento alostérico da proteína, facilitando a entrada de substrato ao sítio catalítico da molécula. / Abstract: The 9a5c strain from bacterium Xylella fastidiosa was the first phytopathogen to have its genome completely sequenced, which revealed a lot of information about its metabolism and its pathogenicity. 'From a variety of orfs encoded by this bacterium, we highlight, in this work, the XF0703, which correlated protein (with 28.3 kDa) has similarity with SurE proteins from several other bacteria. The SurE proteins *are nucleotidases that dephosphorylate various monophosphorylated nucleosides to their respective nucleosides. This function is critical for maintaining the balanced pool of four (deoxy) ribonucleosides for DNA and RNA synthesis. In this work, we describes the cloning of the XF0703 orf into the vector pET29a, the recombinant protein overexpression (XfSurE) in Escherichia coli BL21(DE3) and the protein purification by nickel affinity chromatography. The secondary structure analysis was done by circular dichroism, while oligomeric state determination was achieved by gel filtration chromatography and small-angle X-ray light scattering (SAXS), which showed that the protein is a tetramer. Functional characterization data indicate that the protein has a highest activity at neutral pH in the presence of manganese as a cofactor, with a highest affinity for the 3-AMP substrate (K0,5 = 0,16 mM). Furthermore, kinetic tests showed that the protein has a allosteric behavior with a high positive cooperativity (Hill coefficient around 2.6) for all natural substrates screened (3-AMP, 5'-dAMP, 5'-AMP and 5'-GMP). Experiments with SAXS technique have allowed to calculate the radius of gyration (32.7 ± 0.2 A), maximum intramolecular distance (100 A) and molecule symmetry. / Doutorado / Genetica de Microorganismos / Doutor em Genetica e Biologia Molecular
97

Pre-Steady State Kinetics of the NAD-Malic Enzyme from Ascaris suum in the Direction of Oxidative Decarboxylation of L-Malate

Rajapaksa, Ranjani, 1949- 12 1900 (has links)
Stopped-flow experiments in which the NAD-malic enzyme was preincubated with different reactants at near saturating substrate concentrations suggest a slow isomerization of the E:NAD:Mg complex. The lag is eliminated by preincubation with Mg˙² and malate suggesting that the formation of E:Mg:Malate either bypasses or speeds up the slow isomerization step. Circular dichroic spectral studies of the secondary structural changes of the native enzyme in the presence and absence of substrates supports the existence of conformational changes with NAD˙ and malate. Thus, a slow conformational change of the E:NAD:Mg complex is likely one of the rate-limiting steps in the pre-steady state.
98

The druggable antimalarial target 1-deoxy-D-xylulose-5-phosphate reductoisomerase: purfication, kinetic characterization and inhibition studies / Drugable antimalarial target 1-deoxy-D-xylulose-5-phosphate reductoisomerase

Goble, Jessica Leigh January 2011 (has links)
Plasmodium falciparum 1–deoxy–D–xylulose–5 phosphatereductoisomerase (PfDXR) plays a role in isoprenoid biosynthesis in the malaria parasite and is absent in the human host, making this parasite enzyme an attractive target for antimalarial drug design. To characterize PfDXR, it is necessary to produce large quantities of the enzyme in a soluble and functional form. However, the over–production of malarial proteins in prokaryotic host systems often results in the formation of truncated proteins or insoluble protein aggregates. A heterologous expression system was developed for the production of active PfDXR using codon harmonization and tight control of expression in the presence of lac repressor. Yields of up to 2 mg/l of enzyme were reported using the optimised expression system, which is 8 to 10– fold greater than previously reported yields. The kinetic parameters Km, Vmax and kcat were determined for PfDXR; values reported in this study were consistent with those reported in the literature for other DXR enzymes. A three–dimensional model of the malarial drug target protein PfDXR was generated, and validated using structure–checking programs and protein docking studies. Structural and functional features unique to PfDXR were identified using the model and comparative sequence analyses with apicomplexan and non–apicomplexan DXR proteins. Residues Val44 and Asn45, essential for NADPH binding; and catalytic hatch residues Lys224 and Lys226, which are unique to the species of Plasmodium, were mutated to resemble those of E. coli DXR. Interestingly,these mutations resulted in significant reductions in substrate affinity, when compared to the unmutated PfDXR. Mutant enzymes PfDXR(VN43,44AG) and PfDXR(KK224,226NS) also demonstrated a decreased ability to turnover substrate by 4–fold and 2–fold respectively. This study indicates a difference in the role of the catalytic hatch of PfDXR with regards to the way in which it captures substrates. The study also highlights subtle differences in cofactor binding to PfDXR, compared with the well characterized EcDXR enzyme. The validated PfDXR model was also used to develop a novel efficient in silico screening method for potential tool compounds for use in the rational design of novel DXR inhibitors. Following in silico screening of 46 potential DXR inhibitors, a two–tiered in vitro screening approach was undertaken. DXR inhibition was assessed for the 46 novel compounds using an NADPH– ependant DXP enzyme inhibition assay and antimalarial potential was assessed using P.falciparum–infected erythrocyte growth assays. Select compounds were tested in human cells in order to determine whether they were toxic to the host. From the parallel in silico and in vitro drug screening, it was evident that only a single compound demonstrated reasonable potential binding to DXR (determined using in silico docking), inhibited DXR in vitro and inhibited P. falciparum growth, without being toxic to human cells. Its potential as a lead compound in antimalarial drug development is therefore feasible. Two outcomes were evident from this work. Firstly, analogues of known antimalarial natural products can be screened against malaria, which may then lead towards the rational design of novel compounds that are effective against a specific antimalarial drug target enzyme, such as PfDXR. Secondly, the rational design of novel compounds against a specific antimalarial drug target enzyme can be untaken by adopting a coupled in silico and in vitro approach to drug discovery.
99

Time course analysis of complex enzyme systems

Rentergent, Julius January 2015 (has links)
In studies of enzyme kinetics, reaction time courses are often condensed into a single set of initial rates describing the rate at the start of the reaction. This set is then analysed with the Henri-Michaelis-Menten equation. However, this process necessarily removes information from experimental data and diminishes its statistical significance due to a reduction of available data points. Further, if the examined system does not approach steady-state rapidly, the application of the steady-state-assumption can lead to flawed conclusions. Here, the analysis of two complex enzyme systems by numerical integration of kinetic rate equations is demonstrated. DNA polymerase catalyses the synthesis of DNA in a reaction that involves two substrates, DNA template and dNTP, both of which are highly heterogeneous in nature. The tight binding of DNA to DNA polymerase and its polymer properties prohibit the application of the initial-rate approach. By combining an explicit DNA binding step with a steady-state dNTP incorporation on a template of finite length, the DNA binding parameters and the dNTP incorporation steady-state parameters were estimated from processive polymerisation data in a global regression analysis. This approach is described in Chapter 2 and the results are in good agreement with previously published values. Further properties were investigated in studies of the temperature dependence and solvent isotope dependence of the kinetics. The processive polymerisation of DNA template was monitored using the fluorophore PicoGreen in a simple and inexpensive method described in Chapter 3. The catalytic cycle of ethanolamine ammonia lyase involves the homoloysis of the Co-C bond within the intrinsic B12 cofactor. This homolysis results in the formation of a Co(II)-adenosyl radical intermediate, which can be monitored using stopped-flow spectroscopy. The stopped-flow transients observed for EAL and related enzymes have long been difficult to analyse and interpret, possibly due to rapid methyl group rotation on the substrate. In Chapter 4 of this thesis we were able to rationalise this behaviour using numerical integration of the rate equations of a branched 16-state-kinetic model to fit stopped-flow transients in a global regression analysis. We were able to determine some intrinsic rate constants, and showed that the initial hydrogen atom transfer step is unlikely to have an inflated primary kinetic isotope effect, despite previous claims. More generally, this study demonstrates that the numerical integration analysis used here is likely to be applicable to a broad range of enzyme reaction kinetics.
100

Systems biology informatics for the development and use of genome-scale metabolic models

Swainston, Neil January 2012 (has links)
Systems biology attempts to understand biological systems through the generation of predictive models that allow the behaviour of the system to be simulated in silico. Metabolic systems biology has in recent years focused upon the reconstruction and constraint-based analysis of genome-scale metabolic networks, which provide computational and mathematical representations of the known metabolic capabilities of a given organism. This thesis initially concerns itself with the development of such metabolic networks, first considering the community-driven development of consensus networks of the metabolic functions of Saccharomyces cerevisiae. This is followed by a consideration of automated approaches to network reconstruction that can be applied to facilitate what has, until recently, been an arduous manual process. The use of such large-scale networks in the generation of dynamic kinetic models is then considered. The development of such models is dependent upon the availability of experimentally determined parameters, from omics approaches such as transcriptomics, proteomics and metabolomics, and from kinetic assays. A discussion of the challenges faced with developing informatics infrastructure to support the acquisition, analysis and dissemination of quantitative proteomics and enzyme kinetics data follows, along with the introduction of novel software approaches to address these issues. The requirement for integrating experimental data with kinetic models is considered, along with approaches to construct, parameterise and simulate kinetic models from the network reconstructions and experimental data discussed previously. Finally, future requirements for metabolic systems biology informatics are considered, in the context of experimental data management, modelling infrastructure, and data integration required to bridge the gap between experimental and modelling approaches.

Page generated in 0.0855 seconds