In Sweden about 26000 people are affected by myocardial infarction (MI) every year. Coronary vascular diseases and cerebrovascular diseases with blood flow disruption caused by thrombi are actually the most common cause of death. A contributing mechanism may be if the fibrinolytic system is uncapable to dissolve clots and it might in turn be related to the high amount of plasminogen activator inhibitor 1 (PAI-1) released from platelets. This study investigated if there is any difference between the thrombin activation of the platelet protease activated receptors (PAR) PAR1 and PAR4 concerning PAI-1 secretion. An ELISA assay was modified in order to measure PAI-1 released from stimulated platelets. Concerning PAI-1 secretion this study concluded that PAR1 activation is slightly more sensitive to PAI-1 secretion than PAR4. Both thrombin receptors are really potent in this respect, activating only one of PAR1 or PAR4 is enough to get a strong response. This study could also confirm that platelet PAR1 undergoes desensitization when stimulated with a low dose of agonist. Despite platelets poor protein synthesis machinery it seems like they have the ability to synthesize large amounts of PAI-1.

<p>Density functional theory is employed to study the reaction mechanisms of different epoxide-transforming enzymes. Calculations are based on quantum chemical active site models, which are build from X-ray crystal structures. The models are used to study conversion of various epoxides into their corresponding diols or substituted alcohols. Epoxide-transforming enzymes from three different families are studied. The human soluble epoxide hydrolase (sEH) belongs to the α/β-hydrolase fold family. sEH employs a covalent mechanism to hydrolyze various epoxides into vicinal diols. The <em>Rhodococcus erythrobacter </em>limonene epoxide hydrolase (LEH) constitutes a novel epoxide hydrolase, which is considered the founding member of a new family of enzymes. LEH mediates transformation of limone-1,2-epoxide into the corresponding vicinal diol by employing a general acid/general base-mediated mechanism. The<em> Agrobacterium radiobacter </em>AD1 haloalcohol dehalogenase HheC is related to the short-chain dehydrogenase/reductases. HheC is able to convert epoxides using various nucleophiles such as azide, cyanide, and nitrite. Reaction mechanisms of these three enzymes are analyzed in depth and the role of different active site residues is studied through<em> in silico</em> mutations. Steric and electronic factors influencing the regioselectivity of epoxide opening are identified. The computed energetics help to explain preferred reaction pathways and experimentally observed regioselectivities. Our results confirm the usefulness of the employed computational methodology for investigating enzymatic reactions.</p>

<p>This thesis describes the improvement of two radically different cellulose materials, paper and artificial blood vessels, constructed from two diverse cellulose sources, wood pulp and <em>Acetobacter xylinum</em>. The improvement of both materials was possible due to the natural affinity of the hemicellulose xyloglucan for cellulose.</p><p>Chemical and mechanical pulps were treated with xyloglucan in the wet-end prior to hand sheet formation or by spray application of dry hand sheets, loading a comparable amount of xyloglucan. The tensile strength increases for the wet-end treatment and spray application were 28% and 71% respectively for bleached soft wood, compared to untreated sheets (20.7 Nm/g). The corresponding strength increases for hand sheets made of thermo-mechanical pulp were 6% and 13% respectively compared to untreated sheets (42.4 Nm/g). The tendency for chemical pulp to be superior to mechanical pulp with respect to strength increase was valid even for tear strength and Scott-Bond. These results suggest, in agreement with other studies, that adhesion of xyloglucan to wood fibres is dependent on their degree of surface lignification.</p><p>Also, a method was developed to increase the blood compatibility of artificial blood vessels constructed of bacterial cellulose. Xyloglucan was covalently linked to the endothelial cell adhesion motif (Arg-Gly-Asp). To obtain this, new solid-phase coupling chemistry was developed. Xyloglucan oligosaccharides (XGO) were transformed into XGO-succinamic acid via the corresponding XGO--NH₂derivative prior to coupling with the N-terminus of the solid-phase synthesised Gly-Arg-Gly-Asp-Ser peptide. The resin-bound glyco-peptide was then cleaved and enzymatically re-incorporated into high molecular weight xyloglucan. The glyco-peptide was further adsorbed onto bacterial cellulose scaffolds, increasing the adhesion and proliferation of endothelial cells and therefore blood compatibility.</p>

<p>Enzymes are successfully employed in the synthesis of different types of polymers. Candida antarctica lipase B is a highly efficient catalyst for the synthesis of polyesters by ring opening polymerization. ω-Pentadecalactone is an interesting lactone due to the unique proprieties of its polymer (poly-pentadecalactone). These polymers have not been applied in any industrial application due to the difficulties to reach them by chemical polymerization. Enzymatically, poly-pentadecalactone macromonomers can be obtained to high conversion.</p><p>In this investigation we synthesized difunctionalized poly-pentadecalactone with different functional groups. Taking advantage of the selectivity of Candida antarctica lipase B, we introduced different functional end groups. α,ω-Difunctionalized poly-pentadecalactone macromonomers with two thiol ends, two (meth)acrylate ends or with one thiol and one acrylate end were obtained with a high degree of functional ends. We have improved the difunctionalization procedure to a single-step route for the synthesis of α,ω-functionalized poly-pentadecalactones. This procedure has a great potential for industrial applications due to the simplicity of the process and the clean products afforded. Macromonomers with functionalized ends can be used to obtain new polymer architectures with novel proprieties.</p><p>We also show how the use of enzymes could have some limitations when using an initiator with a cleavable ester bond. 2-Hydroxyethyl methacrylate (HEMA) was used as initiator for the ring opening polymerization (eROP) of ε-caprolactone and ω-pentadecalactone aiming for methacrylate functional polyester. However, the lipase catalyzed not only the ring opening polymerization but also the cleavage of the HEMA moiety resulting in a mixture of polymer products with various end groups. A kinetics study of the eROP and the transesterification processes when using HEMA showed that the transesterification processes occurs at moderate frequency at low monomer concentration, it becomes dominant at longer reaction times. We showed that fully difunctionalized polymers can be obtained when using HEMA as initiator for the eROP of lactones by adding a proper end capper.</p>

<p> </p><p>The present thesis is based upon two papers concerning the core-valence double onization of molecular oxygen and mutual neutralization of H⁺ and H^- ions at low collision energies.</p><p>The former of these processes has been studied for the first time using a magnetic bottle time-of-ight electron coincidence spectrometer in combination with<em> ab initio</em> electronic structure calculations. The core-valence photoelectron spectra have been interpreted by comparing with the calculated double ionization energies, as well as the conventional valence band spectrum. Based on this comparison, some general features of the process are discussed and assignments for several of the dicationic states proposed.</p><p>The latter process has been studied by means of a molecular close coupling approach in which both the nuclei and the electrons have been treated at a quantum mechanical level of theory. Accurate <em>ab initio</em> potential energy curves and non-adiabatic couplings have been used to calculate the neutralization cross section in the collision energy region 0.001 to 100 eV. Special emphasis has been put on the energy region below a few eV from which the low temperature rate coe_cient is evaluated. In this region, the calculated neutralization cross section is in good agreement with several other theoretical studies, but is a factor of two to three lower than the only published experimental data.</p><p> </p>

Ph.D. afhandling, Roskilde universitetscenter 2002.

Ph.D. afhandling, Roskilde universitetscenter 2003.

Perchlorate and chlorate are naturally occurring in the atmosphere, from here it sediments into groundwater and soil. The pollution is increased by discharges of perchlorate and chlorate from agriculture and paper mills. Bacteria capable of reducing perchlorate and chlorate to chloride and oxygen can be used to get rid of these contaminants. However an anaerobic environment needs to be sustained in order for this reaction to be used. For this reduction to work in an aerobic environment as well, a greater knowledge of the reducing enzymes, regulating factors and their corresponding genes is needed. One of these enzymes is called chlorite dismutase. The upstream region of this gene in Ideonella dechloratans bacteria is likely to contain a promoter sequence. The purpose of this work was to shorten this DNA sequence to get closer to the potential regulatory sequences and binding-site for RNA polymerase. Subsequently control if the sequence was active as an promoter. The potential promoter region was shortened and amplified by PCR. It was then ligated into the plasmid pRU1103which is carrying a reporter gene. Cloning of the construction into Escherichia coli resulted in a production of the reporter gene product. This indicates that the sequence contained a working promoter.

Oxochlorates are anions with a partially naturally occurrence in nature but are also spread by human activities, including the paper industry. These compounds are harmful to both nature and humans, which makes it necessary to find a good way for their degradation. There are two different kinds of bacteria that can use oxochlorates as electron acceptors in their metabolism, bacteria that break down perchlorate and bacteria that break down both perchlorate and chlorate. A bacterium that can break down chlorate under anaerobic conditions is Ideonella dechloratans which holds the genes for chlorite dismutase and chlorate reductase which are enzymes for the degradation of chlorate. Gene expression and enzyme activity of chlorite dismutase are induced under anaerobic conditions, which makes it interesting to find out how this regulation functions in order to better exploit these bacteria in biological wastewater treatment. To study the expression of the gene for chlorite dismutase a potential promoter and regulatory sequence has previously been cloned in a reporter vector and transformed into Escherichia coli (E.coli) bacterium XL-1 blue. This work was to develop a β-galactosidase assay for the quantification of gene expression in this system and apply it to aerobic and anaerobic bacterial cultures. The method was optimized for cultivation in LB-medium and measurements of gene expression showed higher promoter activity during anaerobic compared with aerobic culture conditions for all of the studied clones. This means that all the clones contain a sequence which can function as promoter in E. coli, and that its activity increases during anaerobic conditions.

Enzymes are powerful biocatalysts that provide rate accelerations of up to 1019 fold compared to the corresponding uncatalyzed reaction in solution. The origin of the remarkable performance displayed by enzymes has fascinated and puzzled researchers for over a hundred years. It is clear that the catalytic effect is a consequence of the higher degree of transition state stabilization for the enzyme catalyzed reaction compared to the corresponding uncatalyzed reaction. It is still not well understood exactly how this transition state stabilization occurs and the relative importance of various catalytic effects are discussed. Catalytic effects involving electrostatics, near attack conformers, dynamic effects and an economy in atomic motion are discussed in this thesis. The importance of electrostatic effects is corroborated in this thesis. A single hydrogen bond in transition state constitutes an important difference between amidases and esterases. A hydrogen bond in transition state is found in all sixteen analyzed amidases representing ten different reaction mechanisms and eleven different folding families. The hydrogen bond is shown to be either substrate assisted or enzyme assisted. The role of this hydrogen bond is to assist nitrogen inversion in amidases. Esterases lack this interaction in transition state and therefore they are very poor catalysts in the hydrolysis of amides. Electrostatic interactions are found to facilitate proton transfer that enhances the rate of lipase catalyzed N-acylation of amino alcohols. In this thesis electrostatic effects in the substrate are shown to be important for the lipase catalyzed transacylation of acrylates The α,β-double bond present in acrylates introduce electronic effects that has the consequence of restricting the conformational freedom of the substrate in its ground state to two flat conformations, s-cis and s-trans. It is shown that acrylates form near attack conformers (NACs) from their ground state s-cis/s-trans planar conformations. The ability of the enzyme to accommodate such apparent s-cis/s-trans substrate conformations dictates the probability to form productive transition states and thus the reaction rate. Dynamic effects are important in enzymes. In this thesis it is found that a point mutation increases the flexibility of a neighbouring residue in Candida antarctica lipase B. This allows the mutated enzyme to explore conformations not accessible for the wild-type enzyme. The dynamics has the effect to decrease steric interactions in transition state with concomitant rate increase for the transacylation of methyl methacrylate. In this thesis an economy of atomic motion during enzyme catalysis is observed. Nitrogen inversion in amidases constitutes an interesting example. A rotation as part of the reaction mechanism for amide bond hydrolysis would involve much more motion. / QC 20110512