Os sedimentos aquáticos podem fornecer importantes subsídios na avaliação dos ecossistemas aquáticos lênticos, uma vez que grande parte dos nutrientes se encontra no estado sólido. A ocorrência de uma floração de cianobactérias tóxicas originada no Blang, segundo de três reservatórios em cascata do Sistema Salto de Hidrelétricas, localizado no município de São Francisco de Paula (RS), motivou a investigação das possíveis fontes de nutrientes, especialmente de fósforo (P) que foi identificado como limitante para a eutrofização. Foram investigadas fontes de origens difusas (solos, águas e sedimentos dos tributários) e pontuais (uso urbano e a carga interna representada pelo sedimento do leito dos reservatórios). Os resultados mostraram características oligotróficas nas fontes externas e a presença de P disponível em excesso no sedimento do leito, indicando que a carga interna poderia ser uma fonte significativa de nutrientes. A possibilidade de circulação da água hipolimnética foi investigada através de números adimensionais e características físicas do corpo de água, demonstrando que dificilmente ocorreria, uma vez que somente eventos climáticos extremos poderiam provocar a inversão da massa líquida. Excluídas as fontes externas, os resultados sugerem que a fertilização do reservatório Blang tenha sido causada pela abertura da comporta de fundo do reservatório Divisa, localizado imediatamente à montante, durante uma estiagem. O segundo objetivo desta pesquisa foi avaliar a importância dos agregados de partículas e da seleção granulométrica para a análise química de nutrientes em sedimentos aquáticos. Resultados obtidos em sedimentos de ambientes lóticos e lênticos (Sistema Salto, RS), demonstraram que os agregados maiores (465 - 63 μm) concentram nitrogênio nos ambientes lênticos, por isso a análise deve ser realizada, preferencialmente, na fração ≤ 465 μm em sedimentos de ambientes lênticos e na fração ≤ 63 μm dos ambientes lóticos. O último objetivo deste estudo foi testar os efeitos da oxidação sobre a capacidade e a velocidade da sorção de fosfato em sedimentos aquáticos orgânicos, identificando as melhores condições para retenção. Foram utilizados sedimentos aquáticos siliciclásticos de origens distintas, principalmente no que se refere ao clima e à origem do conteúdo orgânico, alóctone e autóctone, representados pelos tipos Dy (Reservatório Divisa, RS) e Sapropel (Reservatório de Tapacurá, São Lourenço da Mata, PE) respectivamente. O experimento foi realizado em suspensões de sedimentos mantidos sob níveis de potencial redox compreendidos entre - 200 mV e + 400 mV. Resultados demonstram que a sorção de fosfato é maior no sedimento tipo Dy em condições reduzidas e no Sapropel em condições oxidadas. / Water-borne sediments can provide important information for evaluating lentic aquatic ecosystems because a large proportion of their nutrients are found in the solid phase. A toxic algal bloom in the Blang Reservoir, the second of three in the Salto System chain of hydroelectric dams located in Sao Francisco de Paula in Rio Grande do Sul, Brazil, motivated the investigation of possible nutrient sources, especially phosphorus, which was identified as the limiting nutrient for eutrophization. Non-point sources, including soil, water and sediment carried by tributaries, and point sources, including urban areas and the internal load from the reservoir bottom, were examined. Results showed oligotrophic characteristics in the external sources and excess P availability in bottom sediments, indicating that the internal load may be a significant source of nutrients. The possible circulation of hypolimnic water was investigated using adimensional numbers and physical characteristics of the body of water, demonstrating that this is unlikely to occur, since only extreme climatic events could cause inversion of the liquid mass. By excluding external sources, results suggest that the fertilization of the Blang Reservoir was most likely caused by the opening of the floodgates from the Divisa Reservoir immediately upstream during a drought period. The second goal of this study was to evaluate the importance of particle aggregates and particle size selection for chemical analyses of nutrients and water-borne sediments. Results from sediments in lentic and lotic environments from the Salto System show that the larger aggregates (465 - 63 μm) concentrate nitrogen under lentic conditions and that, therefore, analyses should be performed on the fraction smaller than 465 μm in lentic environments and in the fraction ≤ 63 μm in lotic environments. The final objective of this study was to test the effects of oxidation on the phosphate sorption capacity and rate in organic aquatic sediments, identifying the best conditions for retention. Silicate aquatic sediments from different origins in terms of climate and source of organic content (allochtonous or autochtonous) were used, and were represented by the types Dy (Divisa Reservoir, RS) and Sapropel (Tapacurá Reservoir, São Lourenço da Mata, PE), respectively. The experiment was carried out in suspended sediment maintained under levels of redox potential between –200mV and +400mV. Results demonstrated that phosphate sorption is greatest in sediment type Dy under reduced conditions and in Sapropel under oxidized conditions.

Heme-substituted horseradish peroxidases and myoglobins were reconstituted from the apoenzyme using mesoheme and diacetyldeuteroheme. X-ray absorption spectroscopy was used to determine the dimensions of the active sites of these heme-substituted proteins, and were compared with those of the proto-hemeproteins. The change in the active-site structure corresponded with the electron withdrawing and donating effects of the different side chains. The oxidation-reduction potentials of Fe4+/Fe3+ couples of the heme-substituted proteins were measured at pH 7 with K2IrC16. The oxidation-reduction potential sequence for compound I/compound II was diacetyldeutero-> proto-> meso-in horseradish peroxidase. The oxidation-reduction potential sequence for compound II /ferric was meso-> proto-> diacetyldeutero-in both HRP and myoglobin. These results indicate that the oxidation of ferric to ferryl form may be related to a radical mechanism. A net charge theory was also proposed to explain these results.

The sarcoplasmic reticulum is an internal membrane system that controls the Ca²⁺ concentration inside muscle cells, and hence the contractile state of both skeletal and cardiac muscle. A key protein that that regulates the Ca²⁺ concentration in this membrane is known as the calcium release channel (CRC). The effects on Ca²⁺ dependent activation is of major importance in the study of CRC since other channel modifiers cannot effect the channel in the absence of Ca²⁺, or they require Ca²⁺ for maximum results. In this study of the high-affinity Ca²⁺ binding site, expected increases in total binding and shifts in the sensitivity of the channel to Ca²⁺ were observed when the pH increased or the solution redox status became more oxidative. Ranolazine, a drug used for treating Angina Pectoris (chest pain), desensitized the cardiac CRC activation but had no effect on the skeletal CRC. This selective desensitization may be the cause of Ranolazine's beneficial therapeutic effects. Both Ranolazine, and homocystein thiolactone (HCTL), a naturally occurring derivative of homocysteine, alters Ca²⁺ dependent activation by calcium without changing the number of channels found in the open state. Surprisingly the effect of HCTL was observed only in a reduced redox potential which leads to speculation that the formation of an alpha-carbon radical by HCTL on the cardiac CRC only occurs if select thiols are in a reduced state.

This study looks at relationships along the hydrologic gradient between and within six pools; including the vegetation community, soil characteristics and hydrology. Pool conditions were monitored weekly throughout the 2011 and 2012 growing seasons. Each pool was equipped with permanent platinum-tipped redox probes to quantify the severity and duration of soil reduction. We described and analyzed 12 soil profiles in each pool, distributed in summit/upland, basin, and rim/transition positions as defined by the high water line. The pools were systematically surveyed for understory vegetation during the 2012 growing season. Vegetation patterns varied between study areas. No clear pattern of unique vegetation was evident from an ordination of the gradient communities. Time series redox potential data showed a visual relationship to water table fluxuation, but also a dampening effect from soil organic matter content in the basin positions.

Recently, work in ethanol production is exploring the fermentation of syngas (primarily CO, CO2, and H2) following gasification of cellulosic biomass. The syngas fermentation by clostridium microbes utilizes the Wood-Ljungdahl metabolic pathway. Along this pathway, the intermediate Acetyl-CoA typically diverges to produce ethanol, acetic acid, and/or cell mass. To develop strategies for process optimization, a thermodynamic analysis was conducted that provided a detailed understanding of the favorability of the reactions along the metabolic pathway. Thermodynamic analysis provided identification of potentially limiting steps. Once these limiting reactions were identified, further thermodynamic analysis provided additional insights into the ways in which reaction conditions could be adjusted to improve product yield as well as minimize the effect of such bottlenecks. In this way, strategies to enhance product formation were effectively formed. A thermodynamic analysis regarding electron utilization suggested that it would be unlikely that H2 is utilized in favor of CO for electron production when both species are present. Therefore, CO conversion efficiency to products will be sacrificed during syngas fermentation since some of the CO will make electrons at the expense of product and cell mass formation. Furthermore, the analysis showed the thermodynamic difference of ethanol production, acetate production, and acetate to ethanol conversion, at varying reaction conditions, such as at different pH and redox potential levels. These differences were then incorporated into a strategy to optimize production of desired product, improve bioreactor design, and decrease the amount of by-product formed. Based on the thermodynamics analysis, experiments with varying experimental conditions were performed. The results showed that sulfide concentration in the media changed. In order to assess the effects of experimental conditions on syngas fermentation and decrease the experimental variability, experiments with controlled sulfide, redox potential, and pH were designed and the results indicated that these factors play key roles on cell growth, product formation and product distribution. Furthermore, experimental conditions had different effects on fermentation during different phases. For example, cell growth is much better at pH=5.8 than pH=4.5. However, the ethanol production rate at pH=4.5 is better than pH=5.8. A strategy involving controlling the pH and redox potential at different phases was effectively applied to improve ethanol production. This work provided significant insights on how varying experimental conditions can affect the syngas fermentation process.

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京都大学 / 新制・課程博士 / 博士(農学) / 甲第23960号 / 農博第2509号 / 新制||農||1092(附属図書館) / 学位論文||R4||N5395(農学部図書室) / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 中村 公人, 教授 星野 敏, 教授 藤原 正幸 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

Compartmentalization of redox reactions is essential to all life forms. Protein activity can respond to changes in the local redox environment through the reversible oxidation of cysteine thiols. For the majority of cysteines in the proteome, this interaction takes place through equilibration with the glutathione pool; this raises the question whether this redox pool acts as a buffer, or instead as a sensitive media, transducing information from a local physiological state into protein function.

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