A crude enzyme extract (FI) of polyphenol esterase (PPE), obtained from the microbial culture of Aspergillus niger, was partially purified by ammonium sulfate precipitation. The partially purified fraction (FII) was subjected to further purification by ion-exchange chromatography, which resulted in five separated fractions, FIIIa, FIIIb, FIIIc, FIIId and FIIIe), where FIIIa showed the highest PPE activity towards chlorogenic acid, as substrate. The biocatalysis of the PPE with a wide range of mono- and diphenols, as substrates, was shown to inhibit mushroom tyrosinase (PPO) activity. Fraction FIIIa exhibited an inhibitory effect, measured spectrophotometrically, on PPO activity with the monophenols, including 4-hydroxyphenylpyruvic acid and m- and p-cresols and the diphenols, including chlorogenic acid, catechin, 3,4-dihydroxyphenylacetic acid (DHPAA), L-3,4-dihydroxyphenylalanine (L-DOPA), 4-methylcatechol, catechol and caffeic acid; however, using the polarographic method, the inhibition of PPO activity by PPE biocatalysis occurred with the diphenols but not with the monophenols. The selected enzymatic fraction FIIIa was further purified, using size-exclusion chromatography, which resulted in three fractions FIVa, FIVb and FIVc. Although fraction FIVc contained the highest PPE activity, it showed a lack of enzyme stability. Fraction FIIIa was therefore, subjected to further purification by hydrophobic interaction chromatography thereby yielding fractions FVa, FVb, FVc, FVd, FVe, FVf and FVg, where fraction FVc showed the highest PPE activity. The denatured electrophoretic analysis of fraction FVc showed the presence of one major band, with a molecular weight of 60 kDa. The successive purification of PPE resulted in a marked increase in the inactivation of PPO activity with diphenols, as demonstrated by both the lower I50 and inhibition dissociation constant (Ki) values. The purified fraction FVc was shown to exhibit, spectrophotometrically, a competitive and un

The latest generation of fighter aircraft utilizes a 270Vdc power system [1]. Such high voltage DC power systems are difficult to protect with conventional circuit breakers because the current does not automatically go to zero twice per cycle during a fault like it does in an AC power system and thus arcing of the contacts is a problem. Solid state power controllers (SSPCs) are the solid state equivalent of a circuit breaker that do not arc and which can respond more rapidly to a fault than a mechanical breaker [2]. Present SSPCs are limited to lower voltages and currents by the available power semiconductors [8,9]. This dissertation presents design and experimental results for a SSPC that utilizes SiC power JFETs for the SSPC power switch to extend SSPC capability to higher voltages and currents in a space that is smaller than what is practically achievable with a Si power switch. The research started with the thermal analysis of the SSPCs power switch, which will guide the development of a SiC JFET multi-chip power module to be fabricated by Solid State Devices Inc. (SSDI) using JFETs from SiCED and/or Semisouth LLC. Multiple multi-chip power modules will be paralleled to make the SSPC switch. Fabricated devices were evaluated thermally both statically and dynamically and electrically both statically and dynamically. In addition to the SiC module research a detailed design of the high voltage SSPC control circuit capable of operating at 200andamp;ordm;C was completed including detailed analysis, modeling and simulations, detailed schematic diagrams and detailed drawings. Finally breadboards of selected control circuits were fabricated and tested to verify simulation results. Methods for testing SiC JFET devices under transient thermal conditions unique to the SSPC application was also developed.

A greenhouse experiment was carried out to screen for potential effects of transgenic aspen over-expressing a hybrid poplar leaf polyphenol oxidase gene on rhizosphere communities. Heterotrophic plate counts and cultivation-independent methods were used to compare bacterial and fungal populations associated with transgenic PPO over-expressing and unmodified control trees. Total community DNA extracted from rhizosphere soils was used to establish Iibraries containing partial gene sequences that were PCR-amplified from community members, and putative taxonomy was assigned to clones based on similarity to reference sequences. Gene libraries for the bacterial component of the rhizosphere were established using partial 16S rRNA and chaperonin-60 gene sequences, and the fungal community was characterized based on partial 18S rRNA gene sequences. Phylogenetic analysis revealed that bacterial 16S gene libraries were dominated by Alphaproteobacterial sequences, and the CPN-60 gene libraries were dominated by members of the Bacteroidetes/Chlorobi group, illustrating the biases potentially incurred by using a single gene locus to profile microbial diversity. In both CPN-60 and 16S rRNA libraries, only minor components of the bacterial community differed between transgenic and unmodified trees. Comparisons based on library coverage indicated that changes in bacterial community structure between transgenic and unmodified trees were minor in comparison to differences observed between individual trees of the same type, and no significant differences in terms of bacterial species diversity were revealed by the calculated diversity, dominance and evenness indices. In comparison to the bacterial gene libraries, higher coverage of the underlying population was achieved in the fungal 18S libraries. Members of the Zygomycota, Chytridiomycota, Ascomycota, and Basidiomycota were recovered from both libraries. Dominant groups of fungi associated with each tree type were highly similar, although there were some qualitative differences in the recovery of less abundant fungi as a result of the underlying heterogeneity of the fungal population. No clear differences in terms of fungal species richness were associated with transgenic or unmodified trees, although control libraries were characterized by a slightly higher level of dominance. In general, the methods employed revealed only minor differences between the bacterial and fungal communities associated with transgenic and unmodified trees, suggesting that impacts of the transgenic plants on the rhizosphere community were minimal.

Digestive proteases were isolated from the pancreas of the stomachless cunner fish (Tautogolabrus adspersus) and characterized in terms of their physicochemical properties, their ability to hydrolyze native pectin methylesterase (PME) from orange and polyphenol oxidases (PPO) from mushroom and the ability of the cunner enzyme(s) to maintain the stability of orange juice cloud. / The cunner trypsin fraction exhibited exceptional capacity to hydrolyze native proteins versus the bovine trypsin. Incubation of native PME with cunner or bovine trypsin resulted in a loss of 75% or 35% in PME activity respectively. Similarly, a 75% or 55% loss in PPO activity was observed after treatment with cunner and bovine trypsin respectively. Bovine trypsin, however, hydrolyzed the heat-denatured PME and PPO better than the cunner trypsin. Also, there was no reactivation of both PME and PPO activity after treatment with either the cunner or bovine enzyme during storage at 4$ sp circ$C for 3 weeks. However, PPO retained up to 20% or 50% of the initial activity after treatment with cunner or bovine trypsin, respectively. / A 3 x 3 factorial design involving the factors of temperature, enzyme concentration and incubation time carried out gave an r$ sp2$ of 0.92 and 0.95 for cunner and bovine trypsin treated PME respectively. On the other hand, an r$ sp2$ of 0.91 and 0.94 was obtained for the combined effects using cunner and bovine trypsin for PPO inactivation. Validation of the model of PME inactivation measured as the % cloud remaining revealed that the cunner trypsin fraction upheld the cloud stability of cloud juice better than bovine trypsin, with cunner trypsin retaining more than 90% of the cloud whereas the juice treated with bovine trypsin only resulted in a 70% retention of the juice cloud. (Abstract shortened by UMI.)

Les ellagitannins C-arylglucosidiques sont des polyphenols naturels capable d’inhiber totalement la topoisomérase 2, une enzyme ciblée par les chimiothérapies utilisées contre le cancer. La challenge de cette these c’était trouver une approche biomimétique a la synthèse de ces molecules. La synthèse totale de la punicacorteine A, un simple membre de cette classe, a demande le développement de nouvelle méthodologies liée (i) à la chimie des sucres, pour la formation de la liaison C-arylglucosidique sur le glucose en forme ouverte et (ii) à la chimie des phénols pour générer l’unité biarylique en façon atroposelective. L’utilisation de complexes de cuivre-amine a permis de réaliser le couplage. L’étape suivante de la liaison C-arylglucosidation a ainsi pu être étudiée et le composé attendu a pu être obtenu par réaction dans une solution de tampon phosphate. Le dernière étape de la synthèse (galloylation sélective) n’est pas encore réalisée mais, à ce stade, une déprotection permettre d’obtenir un premier ellagitannin C-arylglucosidique naturel, l’épi-punicacortéine A 5-O-dégalloylée. / C-arylglucosidic ellagitannins belong to a family of biologically-active plant-derived polyphenols. Preliminary studies by Prof. Quideau’s group showed that some of these ellagitannins are potent inhibitors of human topoisomerase 2, current target of anticancer chemotherapies. The challenge of this thesis was the development of a biomimetic synthetic approach to this class of molecule. The total synthesis of punicacortein A, a simple member of this class, required the development of novel methodologies related (i) to sugar chemistry, to install the C-arylglucosidic bond on an open chain glucose, and (ii) to phenol chemistry, to generate the biaryl-unit in an atropoisomerically-controlled manner. This issue was addressed by using copper-amine complexes as oxidizing agents. We managed to obtain the C-arylglycosidic compound by reaction in phosphate buffer. At this stage, a single deprotection step led to the first natural C-arylglucosidic ellagitannin, 5-O-degalloyl epipunicacortein A.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第21263号 / 医博第4381号 / 新制||医||1029(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 柳田 素子, 教授 福田 和彦, 教授 木村 剛 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

No description available.

No description available.

No description available.

No description available.