Catalase HPII of Escherichia coli is similar in sequence and structure to other catalases including the conservation of several residues on both the distal and proximal sides of the active center heme. The roles of many residues on the distal side of the heme have been well characterized. By contrast, very few residues on the proximal side of the heme or in the plane of the heme have been investigated. The primary goal of this thesis is to develop a better understanding of the role of the residues and structural features at the core of catalases and in the lateral access channel. The results demonstrate that a break in molecular symmetry does not have any functional significance. Replacing Ile274 with a Cys resulted in the heme being covalently linked to the protein through a Cys-vinyl bond which is hypersensitive to X-ray irradiation being largely degraded within seconds of exposure to the X-ray beam.

Radiation sensitivity of E. coli O157:H7, non-O157 VTEC and Salmonella to low-dose ionizing irradiation was evaluated. Buffer-suspended E. coli O157 and non-O157 VTEC strains showed similar resistance to 300 Gy X-ray treatments, while Salmonella strains were more resistant. A dose of 1 kGy E-beam radiation reduced two groups of non-O157 E. coli mixtures and one E. coli O157:H7 group inoculated in meat by at least 4 log CFU/g. Salmonella showed only a <2 log CFU/g reduction. Sensory attributes of cooked ground beef patties were not affected (p >0.05) by irradiation. However, irradiated raw carcass muscles were more brown (p < 0.05) but displayed less intense off-aroma (p < 0.05) compared to the control during storage. Therefore, a 1 kGy treatment has the potential to improve microbiological safety with minimal effects on sensory properties of beef; it would be a suitable method for treating carcass trim before preparing ground beef.

This study was conducted to evaluate the impact of low-dose irradiation on beef quality and sensory attributes. Beef top rounds (n=10), bottom round flats (n=10), and knuckles (n=18) were collected from a commercial meat processing facility. Paired subprimals were randomly assigned to treated (irradiated) and control (non-irradiated) groups. The treated group was irradiated with a surface dose of 1-1.5 kGy. Following treatment, subprimals were fabricated into thirds and randomly assigned to one of three aging days (0, 14, or 21). After the aging period, subprimal pieces were trimmed, cut into 2.54 cm steaks, and the resulting trimmings were ground to produce 0.113 kg patties. Steaks and patties were randomly assigned to one of two shelf-life days (2 or 4). During retail display, L*, a*, and b* measurements were taken for raw steak and patty color (0, 2, and 4 day). Steaks and patties from all treatments were evaluated by a trained sensory panel for flavor, basic taste, mouthfeel, after-taste, and texture attributes. Steaks and patties were cooked on open-faced grills, and used for cooked color analysis. Samples from across treatments were used for TBARS analysis. Differences in raw steak and patty color were seen among samples. No differences were evident between cooked steak samples; however, cooked patty color differences were observed. Further, numerous palatability attributes were impacted by treatment. Additionally, differences in TBARS values were seen. These results suggest that if chilled subprimals or carcasses were treated with low-dose e-beam irradiation, quality and palatability characteristics could be negatively impacted.

Catalase HPII of Escherichia coli is similar in sequence and structure to other catalases including the conservation of several residues on both the distal and proximal sides of the active center heme. The roles of many residues on the distal side of the heme have been well characterized. By contrast, very few residues on the proximal side of the heme or in the plane of the heme have been investigated. The primary goal of this thesis is to develop a better understanding of the role of the residues and structural features at the core of catalases and in the lateral access channel. The results demonstrate that a break in molecular symmetry does not have any functional significance. Replacing Ile274 with a Cys resulted in the heme being covalently linked to the protein through a Cys-vinyl bond which is hypersensitive to X-ray irradiation being largely degraded within seconds of exposure to the X-ray beam.

Radiation sensitivity of E. coli O157:H7, non-O157 VTEC and Salmonella to low-dose ionizing irradiation was evaluated. Buffer-suspended E. coli O157 and non-O157 VTEC strains showed similar resistance to 300 Gy X-ray treatments, while Salmonella strains were more resistant. A dose of 1 kGy E-beam radiation reduced two groups of non-O157 E. coli mixtures and one E. coli O157:H7 group inoculated in meat by at least 4 log CFU/g. Salmonella showed only a <2 log CFU/g reduction. Sensory attributes of cooked ground beef patties were not affected (p >0.05) by irradiation. However, irradiated raw carcass muscles were more brown (p < 0.05) but displayed less intense off-aroma (p < 0.05) compared to the control during storage. Therefore, a 1 kGy treatment has the potential to improve microbiological safety with minimal effects on sensory properties of beef; it would be a suitable method for treating carcass trim before preparing ground beef.

Newts, such as Notophthalmus viridescens, can regenerate many structures after amputation or injury and have also shown a refractory response to the formation of cancer in tissues that have regenerative capabilities. The mechanisms behind this latter ability have surprisingly not been studied. In the current study, N. viridescens were exposed to a variety of carcinogens in tissue that cannot regenerate with the intention of inducing tumour formation. After testing multiple carcinogens, multiple sites of injection, and two different modes of delivery, no tumours were generated. Consequently, in vitro assays were developed in order to better understand this ability of newt cells to evade transformation. Mouse and newt muscle cells were exposed to DNA damaging agents, such as irradiation and carcinogens, in culture and their response was monitored with respect to the DNA damage response proteins γ-H2AX, p53, and phospho-p53. These proteins are important as they help prevent mutations in the genome from being passed on to daughter cells and potentially generating cells that proliferate uncontrollably, a hallmark of cancer. Preliminary results suggest that after irradiation, γ-H2AX is present in newt cells for a considerably longer period of time in comparison to mouse cells. p53, as well as phospho-p53, appear to be present at a basal level before and after irradiation in newt cells, whereas mouse cells have a distinct increase upon damage and decrease upon repair. The carcinogen treatments also suggest that newt cells have basal levels of expression of these proteins prior to treatment. These studies suggest that newt cells may have a unique profile of these DNA damage response proteins and may be “primed” to repair any future damage. This is a good first step in understanding what is likely a very complicated explanation for newts’ refractory response to cancer formation.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1984. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 147-158).

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 169-172). Also available via the Internet.

abstract: The dissolution of metal layers such as silver into chalcogenide glass layers such as germanium selenide changes the resistivity of the metal and chalcogenide films by a great extent. It is known that the incorporation of the metal can be achieved by ultra violet light exposure or thermal processes. In this work, the use of metal dissolution by exposure to gamma radiation has been explored for radiation sensor applications. Test structures were designed and a process flow was developed for prototype sensor fabrication. The test structures were designed such that sensitivity to radiation could be studied. The focus is on the effect of gamma rays as well as ultra violet light on silver dissolution in germanium selenide (Ge30Se70) chalcogenide glass. Ultra violet radiation testing was used prior to gamma exposure to assess the basic mechanism. The test structures were electrically characterized prior to and post irradiation to assess resistance change due to metal dissolution. A change in resistance was observed post irradiation and was found to be dependent on the radiation dose. The structures were also characterized using atomic force microscopy and roughness measurements were made prior to and post irradiation. A change in roughness of the silver films on Ge30Se70 was observed following exposure. This indicated the loss of continuity of the film which causes the increase in silver film resistance following irradiation. Recovery of initial resistance in the structures was also observed after the radiation stress was removed. This recovery was explained with photo-stimulated deposition of silver from the chalcogenide at room temperature confirmed with the re-appearance of silver dendrites on the chalcogenide surface. The results demonstrate that it is possible to use the metal dissolution effect in radiation sensing applications. / Dissertation/Thesis / M.S. Electrical Engineering 2012

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