Kinetics of some gas phase reactions of halogenated free radicals

The first two chapters of this thesis describe a study of the kinetics of the gas phase addition of perfluoro-isopropyl and perfluoro-t-butyl radicals to various olefins. The radicals were produced by photolysing the corresponding perfluoroalkyl iodides. Temperature variation data allowed determination of relative Arrhenius parameters. The results are compared with the data available for other simple radicals, and a comparison between the radicals of the series CF3•, CF3CF2•, (CF3)2CF• and (CF3)3C •, in particular, gives valuable information as to the relative importance of steric and other effects in free radical addition reactions. Chapter 3 describes an attempt to determine the absolute rate constant for the recombination of perfluoro- isopropyl radicals. The rotating sector method was used, but, due to a certain amount of thermal initiation and to a first order termination process as well as the more usual bimolecular disappearance of the radicals, the simple mathematical treatment, presented by Shepp, could not be applied to our system. A modified treatment was used and the rate constant was determined at 46°c. The result was taken as evidence for an activation energy different from zero for the reaction. Chapter 4 is a study of the orientation of the addition of monoiodomethyl radicals to various fluorinated olefins, at 150°c Di-t-butyl peroxide was thermally decomposed and the methyl radicals produced initiated the free radical addition by astracting ioding for diiodomethane. The results are compared with the date of some related radicals

Interpersonal violence against children in sport in the Netherlands and Belgium

The current article reports on the first large-scale prevalence study on interpersonal violence against children in sport in the Netherlands and Belgium. Using a dedicated online questionnaire, over 4,000 adults prescreened on having participated in organized sport before the age of 18 were surveyed with respect to their experiences with childhood psychological, physical, and sexual violence while playing sports. Being the first of its kind in the Netherlands and Belgium, our study has a sufficiently large sample taken from the general population, with a balanced gender ratio and wide variety in socio-demographic characteristics. The survey showed that 38% of all respondents reported experiences with psychological violence, 11% with physical violence, and 14% with sexual violence. Ethnic minority, lesbian/gay/bisexual (LGB) and disabled athletes, and those competing at the international level report significantly more experiences of interpersonal violence in sport. The results are consistent with rates obtained outside sport, underscoring the need for more research on interventions and systematic follow-ups, to minimize these negative experiences in youth sport

Evaluation of chloroform/methanol extraction to facilitate the study of membrane proteins of non-model plants

Membrane proteins are of great interest to plant physiologists because of their important function in many physiological processes. However, their study is hampered by their low abundance and poor solubility in aqueous buffers. Proteomics studies of non-model plants are generally restricted to gel-based methods. Unfortunately, all gel-based techniques for membrane proteomics lack resolving power. Therefore, a very stringent enrichment method is needed before protein separation. In this study, protein extraction in a mixture of chloroform and methanol in combination with gel electrophoresis is evaluated as a method to study membrane proteins in non-model plants. Benefits as well as disadvantages of the method are discussed. To demonstrate the pitfalls of working with non-model plants and to give a proof of principle, the method was first applied to whole leaves of the model plant Arabidopsis. Subsequently, a comparison with proteins extracted from leaves of the non-model plant, banana, was made. To estimate the tissue and organelle specificity of the method, it was also applied on banana meristems. Abundant membrane or lipid-associated proteins could be identified in both tissues, with the leaf extract yielding a higher number of membrane proteins

Phosphofructo-2-kinase/Fructose-2,6-bisphosphatase Modulates Oscillations of Pancreatic Islet Metabolism

Pulses of insulin from pancreatic beta-cells help maintain blood glucose in a narrow range, although the source of these pulses is unclear. It has been proposed that a positive feedback circuit exists within the glycolytic pathway, the autocatalytic activation of phosphofructokinase-1 (PFK1), which endows pancreatic beta-cells with the ability to generate oscillations in metabolism. Flux through PFK1 is controlled by the bifunctional enzyme PFK2/FBPase2 (6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase) in two ways: via (1) production/degradation of fructose-2,6-bisphosphate (Fru2,6-BP), a potent allosteric activator of PFK1, as well as (2) direct activation of glucokinase due to a protein-protein interaction. In this study, we used a combination of live-cell imaging and mathematical modeling to examine the effects of inducibly-expressed PFK2/FBPase2 mutants on glucose-induced Ca2+ pulsatility in mouse islets. Irrespective of the ability to bind glucokinase, mutants of PFK2/FBPase2 that increased the kinase:phosphatase ratio reduced the period and amplitude of Ca2+ oscillations. Mutants which reduced the kinase:phosphatase ratio had the opposite effect. These results indicate that the main effect of the bifunctional enzyme on islet pulsatility is due to Fru2,6-BP alteration of the threshold for autocatalytic activation of PFK1 by Fru1,6-BP. Using computational models based on PFK1-generated islet oscillations, we then illustrated how moderate elevation of Fru-2,6-BP can increase the frequency of glycolytic oscillations while reducing their amplitude, with sufficiently high activation resulting in termination of slow oscillations. The concordance we observed between PFK2/FBPase2-induced modulation of islet oscillations and the models of PFK1-driven oscillations furthermore suggests that metabolic oscillations, like those found in yeast and skeletal muscle, are shaped early in glycolysis

High-confidence glycosome proteome for procyclic form <em>Trypanosoma brucei</em> by epitope-tag organelle enrichment and SILAC proteomics

The glycosome of the pathogenic African trypanosome Trypanosoma brucei is a specialized peroxisome that contains most of the enzymes of glycolysis and several other metabolic and catabolic pathways. The contents and transporters of this membrane-bounded organelle are of considerable interest as potential drug targets. Here we use epitope tagging, magnetic bead enrichment, and SILAC quantitative proteomics to determine a high-confidence glycosome proteome for the procyclic life cycle stage of the parasite using isotope ratios to discriminate glycosomal from mitochondrial and other contaminating proteins. The data confirm the presence of several previously demonstrated and suggested pathways in the organelle and identify previously unanticipated activities, such as protein phosphatases. The implications of the findings are discussed