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Typescript, etc. / Digitized by Kansas State University Libraries

Typescript, etc. / Digitized by Kansas State University Libraries

The spectral and kinetic properties of Chlorobium thiosulfatophilum cytochrome c-555 have been investigated and are compared to analogous properties of procaryotic and eucaryotic c-type cytochromes. The circular dichroism spectra are similar for c-type cytochromes of a given class and effects arising from specific amino acid substitutions are determined. The oxidation-reduction state dependence of the spectra in the near-ultraviolet region is interpreted in terms of changes in hydrogen bonding and polarity of the environment of aromatic amino acid residues in close proximity to heme iron resulting from small structural changes. An electrostatic model of bimolecular rate constants is developed to adequately describe the electric field effects for accurate computation of intrinsic rate constants. Structural models of bimolecular complexes of cytochrome c and flavodoxin or cytochrome b₅, developed by other investigators, are used to constrain the dielectric coefficients of the electrostatic model. Using these constraints, the relative contributions of ionic and dipolar interactions to the intermolecular electrostatic potential energies are estimated for several c-type cytochrome reactions. The ionic contribution is adequately described by the charged residue interactions in the region of intermolecular contact, and the dipolar contribution is adequately described by the molecular dipole moment. Oxidation-reduction reactions of cytochrome c-555 with small molecule reagents suggest a mechanism of electron transfer that is similar to other c-type cytochromes. In general, electron transfer may be preceded by formation of a bimolecular collision complex or may occur during the collision. Further, the ionic strength dependence of second-order rate constants indicates that molecular electric fields significantly affect the bimolecular reaction rates. Calculated intrinsic rate constants are dependent on the difference between oxidation-reduction potentials of the reactants as predicted by Marcus outer sphere electron transfer theory. The mechanism of reduction of c-type cytochromes by flavodoxin semiquinone is similar to the mechanism of electron transfer reactions involving small molecules. Thus, principles involved in protein-small molecule reactions are also involved in protein-protein reactions.

This work consists of four separate chapters. Although they are seemingly different projects, they have a common feature - the application of organometallic chemistry. 1. Lusianthridin and denbinobin, the phenanthrene derivatives, can be found in plants of the family Orchidaceae. They exhibit cytostatic activity against cancer of human lung and ovarian and against promyelocytic leukemia. Therefore, new synthetic methods for these substances may be applied in research and development of new bioactive compounds. I prepared 9,10- disubstituted phenanthrenes through reactions of biphenylene with alkynes, which were catalyzed by iridium complexes. Phenanthridine derivatives are found naturally in the group benzo[c]phenanthridine alkaloids. The most famous of these include sanguinarine and chelerythrine. Sanguinarine selectively induces apoptosis (planned cell death) of human cancer cells and, therefore, is investigated as a potential antitumor agent. Chelerythrine selectively inhibits protein kinase C, leading again to apoptosis. I have studied reactions of biphenylene with nitriles catalyzed by rhodium complexes that have not been described yet. By this, I prepared a series of 6-substituted phenanthridines. 2. Carboranes are artificially prepared organic compounds of boron, which are not represented in...

Au cours de cette étude, nous avons isolé 4 ADNc codant pour des protéines activatrices putatives de l'APC/C de tomate : SlCCS52A, SlCCS52B, SlCDC20-1, et SlCDC20-2. Des données obtenues par RT-qPCR et par hybridation in situ révèlent des profils d'expression différents au niveau tissulaire mais également au cours du développement du fruit de tomate, suggérant que différentes protéines activatrices pourraient assurer la modulation spatio-temporelle de l'activité de l'APC/C chez la tomate. De plus, les transcrits du gène SlCCS52A s'accumulent plus particulièrement dans le fruit durant la phase d'expansion cellulaire, tandis que les transcrits du gène SlCCS52B sont plutôt présents durant les premiers stades de développement, caractérisés par une forte activité de division cellulaire. Afin de préciser le rôle de SlCCS52A et SlCCS52B dans le contrôle du cycle cellulaire et de l'endocycle chez la tomate, ces gènes ont fait l'objet d'une étude fonctionnelle. La réduction de l'expression de SlCCS52A entraîne une réduction de la taille des fruits et de la taille cellulaire, qui s'accompagne d'une diminution du niveau de ploïdie. La surexpression de ce gène modifie la cinétique de développement des fruits. La mise en place de l'endocycle est retardée, mais l'augmentation de la ploïdie est plus rapide et la croissance relative du fruit est alors plus importante. Enfin, la réduction de l'expression de SlCCS52B entraîne une augmentation de l'expression de SlCCS52A au niveau des fruits, suggérant l'existence de mécanismes compensatoires. L'ensemble de ces résultats montrent que SlCCS52A est impliqué dans la mise en place de l'endoréduplication chez la tomate, et participe au contrôle de l'expansion cellulaire. / In this study, we have isolated 4 cDNAs encoding putative proteins activating the APC/C in tomato: SlCCS52A, SlCCS52B, SlCDC20-1, and SlCDC20-2. Data obtained by RT-qPCR and in situ hybridization revealed different expression profiles in tissues but also during the development of tomato fruit, suggesting that different activator proteins could provide the spatio-temporal modulation of the APC/C activity in tomato. In addition, the SlCCS52A transcripts accumulate especially in the fruit during the cell expansion phase, while transcripts of the SlCCS52B gene are rather present during the early stages of development, characterized by a high activity of cell divisions. To clarify the role of SlCCS52A and SlCCS52B in cell cycle control and endocycle in tomato, we performed a functional analysis of these genes. Reducing the expression of SlCCS52A leads to reduced fruit size and cell size, accompanied by a decrease in the level of ploidy. The overexpression of this gene alters the kinetics of fruit development. The establishment of endocycle is delayed, but the increase in ploidy is faster and the relative growth of the fruit is much more important then. Finally, the reduced expression of SlCCS52B leads to an increased expression of SlCCS52A in fruit, suggesting the existence of compensatory mechanisms. All these results show that SlCCS52A is involved in the establishment of endoreduplication in tomato, and participates in the control of cell expansion.

by Law Yin King. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 63-64). / Abstracts in English and Chinese. / Acknowledgments --- p.i / Abstract --- p.ii / Introduction --- p.3 / Chapter 1 --- Preliminaries --- p.5 / Chapter 1.1 --- The Enveloping von Neumann Algebra and Heredi- tary C*-Subalgebras --- p.5 / Chapter 1.2 --- C*-Crossed Products --- p.9 / Chapter 2 --- Hereditary C*-Subalgebras --- p.14 / Chapter 2.1 --- Polar Decompositions of Bounded Linear Functionals --- p.14 / Chapter 2.2 --- Unique State Extension --- p.19 / Chapter 2.3 --- Two Special Classes of Hereditary C*-Subalgebras --- p.25 / Chapter 3 --- C*-Crossed Products --- p.32 / Chapter 3.1 --- Hereditary C*-Subalgebras and Positive Definite Func- tions --- p.32 / Chapter 3.2 --- The Two Special Classes of Hereditary C*-Subalgebras in C*-Crossed Products --- p.43 / Chapter 3.3 --- Weak Expectations --- p.50 / Bibliography --- p.63

Pak Keung, Chan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 43). / Abstracts in English and Chinese. / Chapter 1 --- Preliminaries --- p.6 / Chapter 1.1 --- Definitions --- p.7 / Chapter 1.2 --- Topological Properties of the Structure Spaces of C*- Algebras --- p.14 / Chapter 1.3 --- "Topological Relations Between P(A), A and Prim(A)" --- p.17 / Chapter 2 --- Topological Properties of the Primal Ideal Spaces of C* - Algebras --- p.18 / Chapter 2.1 --- Topologies on Id(A) --- p.19 / Chapter 2.2 --- Minimal Primal Ideals and Their Topology --- p.31 / Chapter 3 --- Topological Representation of C*-Algebras --- p.37 / Chapter 3.1 --- Introduction --- p.37 / Chapter 3.2 --- Main Results --- p.39 / Bibliography --- p.43