Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item IDENTIFYING AND TRACKING MARINE PROTEIN AND ITS IMPORTANCE IN THE NITROGEN CYCLE USING PROTEOMICS(2011) Moore, Eli Kelly; Harvey, H. Rodger; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Protein comprises the largest compartment of organic nitrogen in the ocean, and makes up a major portion of organic carbon in phytoplankton. Protein has long been thought to be highly labile in the environment and rapidly lost during diagenesis. However, the analysis of dissolved and particulate organic matter with NMR has revealed that much of dissolved and particulate marine organic nitrogen is linked by amide bonds, the very bonds that join amino acids in proteins. Throughout the global ocean, total hydrolysable amino acids (THAAs, the building blocks of proteins) can be measured in the water column and sediments, yet their biosynthetic source has remained elusive. Here, analytical techniques were developed combining protein solubilizing buffer extractions, gel electrophoresis, and proteomic mass spectrometry in order to investigate the biogeochemical significance of marine protein from primary production during transport and incorporation in sediments. These techniques enabled the detection and classification of previously unidentified marine sedimentary proteins. Specific proteins were tracked through the water column to continental shelf and deeper basin (3490 m) sediments of the Bering Sea, one of the world's most productive ecosystems. Diatoms were observed to be the principal source of identifiable protein in sediments. In situ shipboard phytoplankton degradation experiments were conducted to follow protein degradation, and it was observed that individual proteins remained identifiable even after 53 days of microbial recycling. These studies show that proteins can be identified from complex environmental matrices, and the methods developed here can be applied to investigate and identify proteins in degraded organic matter from a broad range of sources. The longevity of some fraction of algal proteins indicates that carbon and nitrogen sources can be tracked down the marine water column to sediments in diatom dominated systems as well as other types of phytoplankton. Using proteomic techniques to understand the marine carbon and nitrogen cycles will become increasingly important as climate change influences the timing, location, and phylogeny of those organisms responsible for oceanic primary production.Item Regulation of macronutrient metabolism by the gastrointestinal tract of ruminants(2006-07-28) El-Kadi, Samer Wassim; Bequette, Brian J; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)We set out to test the hypothesis that the gastrointestinal tract (GIT) of ruminant animals catabolizes amino acids (AAs) preferentially. We sought to determine whether this catabolism represents an obligate requirement, and whether this requirement stems from the need to generate energy or support other metabolic demands. The aim was to determine the composition of macronutrients (AAs, short chain fatty acids, and glucose) utilized by the GIT, and the influence of general and specific nutrient supplies on their routes of metabolism. Increasing protein supply to the small intestine did not alter the total amount of glucose removed by the GIT indicating, that glucose removal and therefore utilization is obligatory. In contrast, the net removal of AAs occurred at a constant proportion of arterial and luminal supplies. This translated to larger amounts of AAs removed from blood circulation, and from the lumen of the small intestine in response to increased small intestinal and blood supplies. In this respect, the net absorption of branched chain AAs was, unlike other essential AAs lower than 100%. Further, glutamate and glutamine net appearance across the whole GIT and small intestine was unaffected by protein supply. The disproportionate utilization of BCAA, glutamate, and glutamine as compared to other AAs suggested that their metabolism occurred toward specific metabolic requirements, possibly energy production. When Krebs cycle metabolism was investigated using individual AAs, glucose, and short chain fatty acids, leucine and valine did not contribute to the flux of Krebs cycle intermediates. Conversely, α-ketoglutarate flux originated mainly from glutamate, and to a lesser extent from glutamine. Though glucose was metabolized to pyruvate and lactate, glucose did not contribute to Krebs cycle intermediates. Overall, these results indicated that glutamate plays an important role in energy metabolism, and in insuring replenishment of Krebs cycle intermediates that leave the cycle via cataplerosis. Yet, the results raised new questions that ought to be addressed in future studies. The fate of glutamine carbon, the metabolic significance of leucine and valine deamination, and the role of glucose partial catabolism to lactate need to be investigated.