Membrane proteins are responsible for a variety of key cellular functions including transport of essential substrates across the membrane, signal transduction, and maintenance of cellular morphology. However, given the size and high hydrophobicity of membrane proteins, along with demanding expression and solubilization protocols that often preclude biophysical studies, novel approaches must be devised for studies of their structure and function. This thesis addresses these issues through several sets of inter-related experiments. We first examine sequence motifs directing -helix packing, wherein the determinants of glycophorin A (GpA) dimerization were identified via TOXCAT assay and the evaluation of GpA-derived peptides. We found that (i) conservative mutations can have significant effects on the oligomerization of glycophorin A; and (ii) residues that introduce more efficiently packed structures that are poorly solvated by lipid leads to improved transmembrane segment dimerization. In a further study, we inquired into the criteria for selection of membrane-spanning -helices by cellular machinery through investigation of hydrophobic helical segments (termed -helices) that we identified in soluble proteins. We found that the number and location of charged residues in a given hydrophobic helix are related to their insertion propensity as membrane-spanning segments. When we applied this criterion to -helices in their intact protein structures, we successfully determined the extent of -helix mutations necessary to convert a soluble protein, in part, to a membrane-inserted protein. Finally, using a three-transmembrane segment construct from the cystic fibrosis transmembrane conductance regulator (CFTR), we performed experiments aimed at optimizing criteria for protein overexpression, including construct design, choice of expression system, growth media, and expression temperature. The overall findings are interpreted in terms of progress towards defining the fundamental characteristics of membrane-spanning -helices - from their primary amino acid sequence to the helix-helix interactions they display in the assembly of biologically-functional membrane protein structures.

Membrane proteins are responsible for a variety of key cellular functions including transport of essential substrates across the membrane, signal transduction, and maintenance of cellular morphology. However, given the size and high hydrophobicity of membrane proteins, along with demanding expression and solubilization protocols that often preclude biophysical studies, novel approaches must be devised for studies of their structure and function. This thesis addresses these issues through several sets of inter-related experiments. We first examine sequence motifs directing -helix packing, wherein the determinants of glycophorin A (GpA) dimerization were identified via TOXCAT assay and the evaluation of GpA-derived peptides. We found that (i) conservative mutations can have significant effects on the oligomerization of glycophorin A; and (ii) residues that introduce more efficiently packed structures that are poorly solvated by lipid leads to improved transmembrane segment dimerization. In a further study, we inquired into the criteria for selection of membrane-spanning -helices by cellular machinery through investigation of hydrophobic helical segments (termed -helices) that we identified in soluble proteins. We found that the number and location of charged residues in a given hydrophobic helix are related to their insertion propensity as membrane-spanning segments. When we applied this criterion to -helices in their intact protein structures, we successfully determined the extent of -helix mutations necessary to convert a soluble protein, in part, to a membrane-inserted protein. Finally, using a three-transmembrane segment construct from the cystic fibrosis transmembrane conductance regulator (CFTR), we performed experiments aimed at optimizing criteria for protein overexpression, including construct design, choice of expression system, growth media, and expression temperature. The overall findings are interpreted in terms of progress towards defining the fundamental characteristics of membrane-spanning -helices - from their primary amino acid sequence to the helix-helix interactions they display in the assembly of biologically-functional membrane protein structures.

No description available.

Thesis (M.S.)--University of Hawaii at Manoa, 2006. / Includes bibliographical references (leaves 89-93). / viii, 93 leaves, bound ill. 29 cm

Dry/CO2 reforming is one the hydrocarbon processes that recently has been interesting due to it is ability of producing a lower synthesis gas ratio (H2/CO). This synthesis gas is a highly significant product since it costs more than 50% of the total capital cost of gas to liquid (GTL) process. However, since this reaction is thermodynamically limited, higher temperature or lower pressure is required to achieve higher conversion. Typically, reaction temperatures between 1073 and 1173 K are used for catalytic dry reforming reactions. Consequently, these extreme temperatures lead to a severe carbon deposition causing a catalyst deactivation which is the major difficulty related to CO2 reforming reaction. This has pushed the efforts to be focused mainly on the development of new catalysts. In fact, dry reforming of propane is an equilibrium-limited reaction which can be shifted to the product side by removing one of the products out of the system which can be achieved using a selective membrane reactor. This research is dedicated to investigate and study the catalytic performance of dry reforming of propane over cobalt-nickel catalyst under the temperature range of 773-973 K. This bimetallic catalyst supported on ??-Al2O3 has been utilized in this research since it exhibits better activity, selectivity, and deactivation resistance than monometallic catalysts. Based on this, the primary aims of this thesis are to examine this catalyst and to study the impact of using membrane reactor. In addition, the reaction mechanism and kinetic are investigated using a fixed-bed reactor. Experimental observations have exposed that the catalyst is offering good results under this reaction. The catalysts analysis has confirmed the presence of metal oxides in the catalyst. However, only at a lower carbon dioxide to propane ratio, i.e. lower than 3.5, a carbon signal has been reported. The activation energy study indicates that the process is unlimited by diffusion. The reaction order for propane and carbon dioxide has been found to be zero and 1.17 respectively. This in turn has indicated that C3H8 activation reaction is taking place rapidly and carbon dioxide is suggested to be involved in the rate determining step. In membrane reactor operation, the production rates for H2 and CO have been reported to increase as the sweep gas flow rate increases. The co-current mode offers higher production rate and more stability than counter-current mode over the range of feed ratio. On the other hand, fixed bed reactor shows stable performance and produces more CO and H2 for both modes.

MBR suppliers are largely recommending NaOCl as the cleaning agent. Despite the popularity of this chemical for membrane cleaning, there is a lack of publications regarding NaOCl optimum cleaning conditions. To properly conduct this optimization study (i.e. obtain the required level of reproducibility and confidence), a rigorous methodology is still required. The potential effect of NaOCl on polymeric materials ageing has drawn attention and recent studies have been dedicated to assess the impact of its exposure on numerous membrane materials (except polyvinylidene fluoride (PVDF)). PVDF and polypropylene (PP) hollow fibers were investigated using unwashed yeast as model fouling solution, while mixture of sodium alginate and bovine serum albumin (BSA) acted as feed solution for PVDF flat sheet. The cleaning efficiency and optimum NaOCl concentration were found to vary between the different membrane materials and between single and cyclical cleanings. During cyclical cleaning, foulant was more difficult to remove. When 2% NaOCl was used, Fourier Transform Infra Red (FTIR) Spectroscopy showed a change in membrane function groups on PVDF flat sheet, indicating ageing occurrence. NaOCl agemg caused changes in membrane properties. PP hollow fibers became more brittle with 60 % elongation decrease after 13 weeks. PVDF flat sheet membrane exhibited two-steps-degradation mechanism; firstly, the removal of its surface modification substance, and secondly, the increase of its hydrophilicity. These results were confirmed by X-ray Photoelectron Spectroscopy (XPS), FTIR Spectroscopy, contact angle and hydraulic measurement. Enzyme is an alternative option for membrane cleaning. However, the enzymatic cleaning study did not present encouraging results. Optimum cleaning efficiency for protease (68%) and amylase (73%) were found to be lower compared to NaOCl cleaning (95%). Lowry and Dubois methods found that residual foulants were present on the membrane after the cleaning process, which caused fouling to occur faster when membrane was re-used.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references (leaves 87-94). Also available in electronic version.

Diss. (sammanfattning) Stockholm : Univ., 2005. / Härtill 4 uppsatser.

Diss. (sammanfattning) Uppsala : Univ., 2003. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst. / Härtill 4 uppsatser.