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京都大学 / 新制・課程博士 / 博士(工学) / 甲第23498号 / 工博第4910号 / 新制||工||1767(附属図書館) / 京都大学大学院工学研究科都市環境工学専攻 / (主査)教授 米田 稔, 教授 高岡 昌輝, 教授 平井 康宏 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Polychlorinated biphenyls (PCBs) are persistent organic pollutants, which were banned several decades ago but still exist in the environment, posing a threat to human health. Previously, joint sealants containing PCBs were used in construction. In this study, the long-term PCB-contaminated soils were from a residential area in Västerås Municipality, where the PCBs have been leaching from buildings to the soil for several years. The objective of this thesis is to investigate the feasibility of using plants to remove PCBs from the contaminated soil at a greenhouse scale, and to use a site-specific guideline model for the risk assessment of this contaminated site. After a literature review, four plant species were selected for the greenhouse cultivation including alfalfa (Medicago sativa L.), white clover (Trifolium repens L.), horseradish (Armoracia rusticana L.) and tobacco (Nicotiana tobacum L.). The plants cultivated in the greenhouse were maintained for 92 days and then the concentrations of PCBs in the initial and remediated soils were analyzed by GC-MS. The results indicate that the selected plant species can enhance the removal of high chlorinated PCBs from soils. In the risk assessment, the contents of PCBs in soils were higher than the calculated site-specific guideline, which means it is urgent to implement measures for protecting residents’ health.

The carbamoyl region of the active site of aspartate transcarbamoylase from Escherichia coli was probed using an enzyme assay in which the two substrates were varied near their respective K_m 's. The inhibitors tested, some synthesized and some commercially available, were chosen to satisfy the structural requirements for binding to either the dicarboxylate or phosphate region with a substituent capable of extending into the carbamoyl region. However, the dicarboxylate based inhibitors were found to bind in an abnormal manner (unlike L-aspartate or succinate on which they were based). The carbamoyl region was found to contain a positively charged side-chain and preliminary results indicate that tetrahedral groups are not preferred over trigonal moieties. It is suggested that electrostatic stabilization of the negative charge which develops in the transition state may be a major factor in promoting catalysis. The identity of this charged group in the carbamoyl region is postulated to be His134 based on available X-ray diffraction data. The binding subsites of the active site of this enzyme were also found to be oriented in essentially the same plane. These results will greatly aid in the design of future mechanism-based inhibitors to this enzyme that may have therapeutic value (at this time the mammalian enzyme is thought to have a similar catalytic mechanism). / Thesis / Master of Science (MS)

R. meliloti carrying defined deletions that remove fix114 form Fix- nodules which are devoid of intracellular bacteria. Occasionally strains which carry these deletions form pink nodules which appear effective in contrast to the normal white ineffective nodules formed by strains carrying fix114 mutations. Bacteria isolated from these pink nodules retain the original deletion and form effective pink nodules when reinoculated onto alfalfa. It is hypothesized that these isolates carry second site mutations which enable the bacteria to overcome the symbiotic block associated with the fix114 mutation. In this work, five independent isolates were examined and were shown to carry second site mutations that suppress the symbiotic ineffectiveness completely on alfalfa and incompletely on sweet clover. The five independent second site revertants can be divided into two classes based on genetic data and on their sensitivity to detergents and both classes were localized to the chromosome of the wild type Rm1021. One such second site revertant allele, sfx-1, was cloned and localized to a large 18 kb BamHI fragment. / Thesis / Master of Science (MS)