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No description available.

<p> In this thesis, two inner shell excitation spectroscopy techniques, inner shell electron energy loss spectroscopy (ISEELS) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy, were used to measure the C ls, N ls and 0 ls spectra of the amino acids, glycine, alanine, cysteine, phenylalanine, proline, threonine, tryptophan and the peptides, Gly-Ala, Lys-Trp-Lys (KWK), and Arg-Gly-Asp (RGD). The spectra are analysed with the aide of ab initio computations using the GSCF3 method. The characteristic spectral features of the specific side chains of amino acids are identified. Differences in the spectra of the gas and solid are related to differences between the neutral gas phase molecule and the zwitterionic solid form. A rationalization of observations of high degree of variability in theN ls spectra of amino acids is proposed. The characteristic spectral signatures of peptide bonds have been identified further by comparing the spectra of small peptides to the spectra of their subunit amino acids. A modified "building block" approach is showed to be very useful in modeling the inner shell excitation spectra of peptides through linear combinations of the spectra of the amino acids residues and peptide bonds. </p> / Thesis / Master of Science (MSc)

Environmental factors, such as diet, can have a significant impact on the health of animals, influencing lifespan, development, and disease progression. The model organism Caenorhabditis elegans is a bacterivore whose development is characterized by an invariant pattern of cell division. This study investigated how C. elegans developmental rate is altered in response to 48 different bacterial diets. The bacterial species studied had a wide range of effects on developmental progression, with some bacteria dramatically decreasing developmental rate, while others caused developmental arrest in early larval stages. From these analyses, Staphylococcus species that caused very slow development of animals in the L1 stage were selected for further characterization. The slow developmental rate observed in these animals was rescued by supplementation with essential amino acids. Genetic analysis revealed that these effects were mediated through TOR signaling and were independent of insulin signaling. Loss of daf-15(raptor), a central component of TOR complex 1, inhibited the rescuing effects of the amino acid supplementation on developmental rate, suggesting that the slow development induced by Staphylococcus could be rescued by activating the TORC1 pathway. Autophagy, negatively regulated by TOR, is increased in worms fed Staphylococcus species, suggesting TOR activity is reduced, and supplementation through amino acids reduced autophagy. These data suggest that TOR signaling is reduced in C. elegans in response to certain bacterial diets, resulting in decreased developmental rate, and that this effect may be due to amino acid deficiency. / Thesis / Master of Science (MSc)

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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1980. / Microfiche copy available in Archives and Science. / Vita. / Bibliography: leaves 231-243. / by Susan Margaret Henrichs. / Ph.D.

<p dir="ltr">The objective of the experiments conducted for this dissertation was to investigate the effects of exogenous enzymes on nutrient digestibility for broiler chickens and growing pigs. These experiments covered the effects of phytase, protease, and carbohydrases on the nutrient availability of various diet types and ingredients, as well as evaluations of regression methods for determining ingredient energy values. One study investigated a factorial of phytase and dietary phytate levels on the ileal digestibility of amino acids (AA) and phosphorus (P) for broilers and pigs. The results of these experiments indicated that phytase improved the ileal digestibility of P (P < 0.05) and all AA (P < 0.05) for broilers regardless of the dietary phytate level, and the ileal digestibility of P (P < 0.05) and many economically important AA (P < 0.05) for pigs. This study did not reveal any significant interactions between phytase and dietary phytate, but there were a number of numerical differences in the relative effect of phytase in the two diet types. In a subsequent experiment the effects of a factorial of phytase and protease on ileal P and AA digestibility were evaluated for growing pigs. Similarly to the first study, phytase was shown to improve the ileal digestibility of P (P < 0.05) and a majority of AA (P < 0.05). There were limited main effects of protease, however, it was found to decrease the digestibility of Lys, Met, and Thr (P < 0.05). There were a number of significant quadratic interactions (P < 0.05) of protease within phytase level, where the necessary concentration of protease to elicit positive effects was dependent on phytase inclusion. The next study evaluated the effects of two carbohydrase blends on the ileal AA digestibility and energy values of soybean meal. Both enzyme blends elicited modest improvements in the ileal and total tract digestibility of energy, but there were limited effects on the energy values of the test diets. Both enzyme blends improved the apparent metabolizable energy of soybean meal, but the blend with lower activity and no protease inclusion produced the greater results with an improvement of 15.2%. These enzyme blends resulted in the improved ileal digestibility of nearly all AA from soybean meal for broilers. The last study was a validation of the three-point model for the regression method against a four-point model over both the same test ingredient inclusion range or smaller range. This evaluation used both canola meal and wheat as test ingredients to evaluate if changes in dietary energy or protein levels affect the results of this method, which are representative of both cereal grains and protein concentrates, respectively. The results indicated that there was no difference in the three and four-point models for either ingredient as long as the overall range of test ingredient concentration was the same in both models. This proved more important for canola meal, as it was more susceptible to problems with the estimates or variability based on changes in inclusion. Based on the results of these experiments, it is clear that phytase can improve the AA digestibility for both pigs and chickens, but care must be taken when combinations are made with protease. These data indicate that the use of carbohydrase blends can improve the nutrient availability of soybean meal, and this could have significant implications in diet formulation. Lastly, the use of the three-point model for the regression method is appropriate, but is dependent on the inclusion level of the test ingredient test ingredient.</p>

The nutritional value of an amino acid (AA) is determined by its bioavailability, however concept of digestibility is mostly used in practical situations. Four studies were conducted to test 2 exogenous factors that were hypothesized to affect the AA digestibility in non-ruminant animals. In study 1, broiler chicks were randomly allotted to 4 dietary treatments of control and distillers dried grains with solubles (DDGS, 20%) diets supplemented or not with a novel mixture of carbohydrases. Results indicated the ability of carbohydrase mixture to increase energy utilization of the DDGS diet, with significant improvements in AA digestibility, consequently improving growth performance of broilers. Study 2 examined effect of the carbohydrase mixture in pigs fed a high DDGS diet. Ileal cannulated growing pigs (n = 8, 64.3 ± 0.5 kg) were allotted to 4 dietary treatments in a replicated 4 Ã 4 Latin Square design. Control and DDGS (40%) diets were supplemented or not with a mixture of carbohydrases. Numeric increases for AA digestibility, along with a decreased tendency of urinary energy output suggested a possibility for improved nutrient utilization in pigs when carbohydrases were supplemented to 40% corn DDGS diet. Collectively, carbohydrase seems less effective for swine applications due to greater water content and consequently a lower viscosity in pig digesta. Next, study 3 showed changes in AA digestibility and endogenous AA losses (EAAL) when pigs were challenged orally with Salmonella enterica serovar Typhimurium. Nursery pigs (n = 48, 17.9 ± 0.5 kg) were randomly assigned to a 2 Ã 2 factorial arrangement consisting of two diets (control or N-free) and inoculation (sterile broth or 9.8 Ã 10^9 CFU of Salmonella). Measurements at 24 and 72 h post-inoculation indicated that AA digestibility of pigs is impaired through the initial phase of Salmonella infection and gradually restored, but not fully by 72 h. Finally, study 4 determined the dynamic fluctuations of EAAL and subsequent AA digestibility in response to Salmonella Typhimurium measured at multiple time points. Ileal cannulated pigs (n = 8, 76.0 ± 1.4 kg) were randomly assigned to either a control or a N-free diet and challenged orally with 1.3 Ã 10^10 CFU of Salmonella. Inflammatory diarrhea was associated with reduced AA digestibility and increased EAAL showing respective peak values at 8-16 h post-inoculation. Alterations in AA digestibility and EAAL were gradually recovered to near pre-inoculation values by 56-64 h post-inoculation, but showed impaired digestibility at 72-80 h post-inoculation. / Ph. D.

The design and discovery of new surface-active polymers that self-assemble on solid substrates to form brush layers will have a major impact on numerous applications. Through recombinant DNA technology, there exists the potential to harness a cell's protein synthesis machinery to produce a brush-forming poly(amino acid) (or PAA) with an exactly specified amino acid sequence, thus controlling the polymer's composition at a level unequaled by conventional organic polymer synthesis. The presented work demonstrates the cloning, expression, purification and characterization of de novo-designed PAA's designed to form brush layers on alumina surfaces. Using conventional recombinant DNA methods, the feasibility of producing a PAA consisting of a poly-glutamate block and a poly-proline block was demonstrated. However, the PAA design was limited by the inherent limitations of conventional cloning techniques. We introduce here the development of a simple and versatile strategy for producing de novo-designed, high molecular weight PAA's using recombinant DNA technology. The basis of this strategy is that small DNA modules encoding for short PAA blocks can be easily inserted directly into a commercially available and unmodified expression vector. The insertions can be made repeatedly until the gene encodes for a polymer of desired molecular weight and composition. Thus, sequential modifications can be made to the PAA without having to re-start the gene assembly process from the beginning, thereby allowing for quick determination of how these changes affect polymer structure and function. The feasibility and simplicity of this method was shown during the production of a PAA, consisting of a long zwitterionic tail block and a short acidic anchor block, designed to form optimal brush layers on alumina surfaces. The success and flexibility of this method indicates that it can be applied for production of de novo-designed polypeptides in general. It is hoped that this method will contribute towards the rapid development of bio-inspired protein-based polymers for a variety of applications. This dissertation also contains research that aimed to use phage display technology to develop a new liposome-based immunoassay against biological toxins. This work was part of a collaboration effort with the U.S. Department of Defense and Luna Innovations. / Ph. D.

M.S.