Characterisation of the structural stability of transketolase under biocatalytically relevant conditions

The enzyme transketolase (TK; E.C. 2.2.1.1) from Escherichia coli occupies a pivotal place in metabolic regulation. TK catalyses the interconversion of sugars by transferring a two-carbon ketol unit from a ketose donor substrate to an aldolase acceptor substrate. It is also an important biocatalyst in stereo-specific carbon-carbon bond synthesis with potential industrial application for the synthesis of pharmaceuticals, agrochemicals and fine chemicals. Although many useful reactions have been reported for TK, many of the substrates and products are unstable or insoluble at the pH or temperature for which the enzyme has optimum activity. Understanding the structural stability of transketolase under bioprocess conditions will improve our capacity to comprehend and ultimately to engineer it to make it work in a broader range of pH or temperature to potentially help in the reduction of process time and to increase the quality and solubility of products. In this research I characterised the early events on the urea denaturation pathway of E. coli transketolase, providing new insights into the mechanisms of enzyme deactivation that occur under biocatalytic conditions. Equilibrium denaturation measurements by fluorescence intensity and circular dichroism (CD), combined with size-exclusion and dynamic light scattering studies, have revealed three transitions in the denaturation pathway for holo-TK. The first step, at low urea concentration corresponds to the local restructuring of the thiamine diphosphate (TPP) binding-sites. Next, the dissociation of the TPP cofactors and partial loss of secondary structure produces a form, which is most consistent with a partially denatured dimeric enzyme. While the enzyme is deactivated initially by changes in structure associated with the cofactors, this event does not release the cofactor from the enzyme, consistent with the intermediate formed during the reconstitution of holo-TK from apo-TK. Improvement of biocatalytic processes using TK over prolonged reaction times would, therefore, need to address the formation of this cofactor-associated intermediate state. Equivalent results were also observed with a high throughput microplate-based fluorescence method that uses less enzyme and time. The equilibrium denaturation of holo and apo-TK at different temperatures and pH was also investigated for further insights into the enzyme stability and to provide a benchmark for assessing any future enzyme variants with altered pH or temperature optima. In an effort to enhance the stability of the enzyme I subsequently used bioinformatical, statistical and multivariate analyses of protein sequences and associated properties to determine the most likely residues to affect temperature and pH optima in biocatalysis. The outcome of this first parametric statistical analysis (Pearson’s r test) rendered 20 different points. Promising mutation points were selected based on the correlation coefficient (r) results taken into account a level of significance α = 0.05. TK E. coli selected points were then mutated and screened by site-saturated mutagenesis (SSM) and automated techniques respectively. Finally alternative statistical correlation methods were examined, including a non-parametric statistical analysis (Kendall’s τ or tau test), principal component analysis (PCA) and partial least square (PLS), for their potential to generate TK mutant variants with either enhanced pH or temperature stability

Assessment of the SBAC atmospheric correction technique applied to Landsat 8-TIRS from ground LST measurements in the Barrax test site

La peculiar estructura y propiedades físico-químicas del silicio poroso nanoestructurado ha estimulado el uso de este material en una amplia variedad de aplicaciones. En el campo de la optoelectrónica, la posibilidad de producir estructuras multicapa en las que cada una de las capas tiene propiedades ópticas particulares, permite la fabricación de filtros ópticos interferenciales con un comportamiento predefinido. En este trabajo se han utilizado estructuras multicapa de silicio poroso para filtrar la luz incidente sobre un sustrato fotosensible de silicio con la intención de modular su respuesta espectral. El comportamiento óptico del filtro de silicio poroso fue simulado antes de su fabricación, y las medidas ópticas demostraron un buen acuerdo entre el comportamiento del filtro obtenido y las predicciones teóricas. Mediciones de fotocorriente han demostrado que los filtros de silicio poroso han reducido el rango espectral de fotosensibilidad del silicio, de los >750 nm originales a unos 150 nm. Filtros con distintos diseños han permitido no sólo estrechar la banda espectral de sensibilidad del detector pancromático de Si, sino también sintonizarla a lo lago de todo el rango visible. El silicio poroso nanoestructurado es compatible con las técnicas convencionales de fabricación microelectrónica, lo que hace posible incorporar estos filtros interferenciales sobre una amplia variedad de sensores y fotodiodos pancromáticos VIS, NIR o SWIR convencionales. Los resultados presentados en este trabajo demuestran que los filtros interferenciales de silicio poroso reestructurado resultan muy prometedores para el desarrollo de sensores multi- e hiperespectrales de bajo costeThe particular structure and physico-chemical properties of nanostructured porous silicon has stimulated the use of this material in many different applications. In the field of optoelectronics, the possibility of fabricating multilayer stacks where each individual layer has different optical properties allows the formation of optical interference filters with a predesigned behavior. In the present work, nanostructured porous silicon interference multilayer structures have been used to filter incident light reaching a Si photosensitive wafer in order to tailor its spectral response. The optical behavior of the porous silicon filters was simulated prior to their fabrication, and optical measurements showed good agreement between the simulated and experimental spectra. Photocurrent measurements have shown that the porous silicon filters narrowed the spectral responsitivity of silicon, from the original value of >750 nm down to around 150 nm. Different filter designs allowed to not only narrowen, but also tune the Si panchromatic sensitivity along the whole visible range. Porous silicon is compatible with standard microelectronic fabrication processes, making it possible to incorporate these interference filters onto a wide variety of conventional panchromatic VIS, NIR or SWIR broad band sensors. These results show that nanostructured silicon interference filters are a promising tool for developing cost-effective multi- and hyperspectral narrowband sensor

Perceived cognitive functioning in breast cancer patients treated with chemotherapy compared to matched healthy women: Evidence from a Portuguese study

Aim: Cognitive concerns are one of the most frequently reported symptoms by breast cancer survivors. This study aimed to evaluate perceived cognitive functioning in Portuguese women with breast cancer treated with chemotherapy. Methods: A cross-sectional study enrolling 146 women (73 with breast cancer and 73 healthy) was conducted from August to October 2017, invited to participate through online dissemination. Participants completed self-reported questionnaires to collect sociodemographic and clinical data and assess perceived cognitive functioning and psychological adjustment variables (anxiety and depression). Results: Compared to healthy women, women with breast cancer showed significantly lower scores on the Functional Assessment of Cancer Therapy-Cognitive Function (FACT-Cog) subscales and higher levels of depression. Both groups showed significant negative correlations between perceived cognitive functioning and anxiety and depression. Health status and depression seem to better explain perceived cognitive functioning, with health status adding significantly more explained variance beyond sociodemographic and psychological adjustment variables. Conclusion: The current findings provide evidence for the existence of more cognitive complaints among Portuguese women with breast cancer, compared to healthy individuals. Anxiety, depression, age and education also explain perceived cognitive functioning. Considering that health status and psychological adjustment seem to significantly explain perceived cognitive functioning, special attention should be given by health-care professionals, including nurses, to designing clinical interventions for breast cancer patients to help manage cognitive impairment

Una nueva asociación de matorral gipsófilo para el Sur de España (Provincia Bética)

El estudio de los matorrales gípsicos en el sur de España, revela la presencia de una comunidad diferente del resto de asociaciones descritas hasta el momento dentro de la alianza Lepidion subulati, al existir diferencias florísticas, ecológicas y biogeográficas. Por ello se propone la asociación Ononido angustifolii-Anthyllidetum cytisoidi nova, con un área subbética e hispalense, que se presenta en ambientes, secos y subhúmedos, sobre substratos gípsicos, los cuales dependiendo del ombrotipo se encuentran más o menos lavados, por lo que el matorral puede presentar más o menos gipsófitos estrictos. Asociación que se desarrolla sobre sustratos gípsicos, los cuales experimentan una pérdida de sales en ambientes seco-subhúmedos, por lo que esta nueva comunidad presenta un bajo porcentaje de gipsófilos estrictos frente a una mayor frecuencia de especies menos estrictas. Por lo que se propone la nueva alianza Resedo constrictae-Helianthemion syriacae nova de distribución ibérico-magrebíA study of the thickets growing on gypsum soils in the south of Spain reveals the presence of a community different from the other associations already described within the suballiance Lepidienion subulati as a result of the floristic, ecological and biogeographical differences. Therefore, we propose the association Ononido angustifolii-Anthyllidetum cytisoidi nova with a Subbetic and Hispalensean distribution. The association occurs in semiarid, dry and subhumid environments, on gypsum soils which, depending on the ombrotype, are more or less washed-out and, consequently, the thicket may comprise more o less strict gypsophytes. The association grows on gypsum soils which undergo salt deprivation in dry-subhumid environments. Thus, in this new community the percentage of strict gypsophilous taxa is low as compared to the number of less strict gypsophytes. To propose the new alliance Resedo constrictae-Helianthemion syriacae iberico-magrebi distribution

Residual stresses and stress corrosion cracking in pipe fittings

Residual stresses can play a key role in the SCC performance of susceptible materials in PWR primary water applications. Residual stresses are stresses stored within the metal that develop during deformation and persist in the absence of external forces or temperature gradients. Sources of residual stresses in pipe fittings include fabrication processes, installation and welding. There are a number of methods to characterize the magnitude and orientation of residual stresses. These include numerical analysis, chemical cracking tests, and measurement (e.g., X-ray diffraction, neutron diffraction, strain gage/hole drilling, strain gage/trepanning, strain gage/section and layer removal, and acoustics). This paper presents 400 C steam SCC test results demonstrating that residual stresses in as-fabricated Alloy 600 pipe fittings are sufficient to induce SCC. Residual stresses present in as-fabricated pipe fittings are characterized by chemical cracking tests (stainless steel fittings tested in boiling magnesium chloride solution) and by the sectioning and layer removal (SLR) technique

The Hahn Quantum Variational Calculus

We introduce the Hahn quantum variational calculus. Necessary and sufficient optimality conditions for the basic, isoperimetric, and Hahn quantum Lagrange problems, are studied. We also show the validity of Leitmann's direct method for the Hahn quantum variational calculus, and give explicit solutions to some concrete problems. To illustrate the results, we provide several examples and discuss a quantum version of the well known Ramsey model of economics.Comment: Submitted: 3/March/2010; 4th revision: 9/June/2010; accepted: 18/June/2010; for publication in Journal of Optimization Theory and Application

Anisotropy at the end of the cosmic ray spectrum?

The starburst galaxies M82 and NGC253 have been proposed as the primary sources of cosmic rays with energies above $10^{18.7}$ eV. For energies \agt 10^{20.3} eV the model predicts strong anisotropies. We calculate the probabilities that the latter can be due to chance occurrence. For the highest energy cosmic ray events in this energy region, we find that the observed directionality has less than 1% probability of occurring due to random fluctuations. Moreover, during the first 5 years of operation at Auger, the observation of even half the predicted anisotropy has a probability of less than $10^{-5}$ to occur by chance fluctuation. Thus, this model can be subject to test at very small cost to the Auger priors budget and, whatever the outcome of that test, valuable information on the Galactic magnetic field will be obtained.Comment: Final version to be published in Physical Review

Constraints on the Progenitor System and the Environs of SN 2014J from Deep Radio Observations

We report deep EVN and eMERLIN observations of the Type Ia SN 2014J in the nearby galaxy M82. Our observations represent, together with JVLA observations of SNe 2011fe and 2014J, the most sensitive radio studies of Type Ia SNe ever. By combining data and a proper modeling of the radio emission, we constrain the mass-loss rate from the progenitor system of SN 2014J to $\dot{M} \lesssim 7.0\times 10^{-10} {\,{M_{\odot } \,\rm yr^{-1}}}$ (for a wind speed of 100 km s-1). If the medium around the supernova is uniform, then n ISM lesssim 1.3 cm-3, which is the most stringent limit for the (uniform) density around a Type Ia SN. Our deep upper limits favor a double-degenerate (DD) scenario involving two WD stars for the progenitor system of SN 2014J, as such systems have less circumstellar gas than our upper limits. By contrast, most single-degenerate (SD) scenarios, i.e., the wide family of progenitor systems where a red giant, main-sequence, or sub-giant star donates mass to an exploding WD, are ruled out by our observations. (While completing our work, we noticed that a paper by Margutti et al. was submitted to The Astrophysical Journal. From a non-detection of X-ray emission from SN 2014J, the authors obtain limits of $\dot{M} \lesssim 1.2 \times 10^{-9}$ M ☉ yr-1 (for a wind speed of 100 km s-1) and n ISM lesssim 3.5 cm-3, for the ρ∝r -2 wind and constant density cases, respectively. As these limits are less constraining than ours, the findings by Margutti et al. do not alter our conclusions. The X-ray results are, however, important to rule out free-free and synchrotron self-absorption as a reason for the radio non-detections.) Our estimates on the limits on the gas density surrounding SN2011fe, using the flux density limits from Chomiuk et al., agree well with their results. Although we discuss the possibilities of an SD scenario passing observational tests, as well as uncertainties in the modeling of the radio emission, the evidence from SNe 2011fe and 2014J points in the direction of a DD scenario for both

Fire-derived organic matter retains ammonia through covalent bond formation

Fire-derived organic matter, often referred to as pyrogenic organic matter (PyOM), is present in the Earth's soil, sediment, atmosphere, and water. We investigated interactions of PyOM with ammonia (NH₃) gas, which makes up much of the Earth's reactive nitrogen (N) pool. Here we show that PyOM's NH₃ retention capacity under ambient conditions can exceed 180 mg N g⁻¹ PyOM-carbon, resulting in a material with a higher N content than any unprocessed plant material and most animal manures. As PyOM is weathered, NH₃ retention increases sixfold, with more than half of the N retained through chemisorption rather than physisorption. Near-edge X-ray absorption fine structure and nuclear magnetic resonance spectroscopy reveal that a variety of covalent bonds form between NH₃-N and PyOM, more than 10% of which contained heterocyclic structures. We estimate that through these mechanisms soil PyOM stocks could retain more than 600-fold annual NH₃ emissions from agriculture, exerting an important control on global N cycling.Rachel Hestrin, Dorisel Torres-Rojas, James J. Dynes, James M. Hook, Tom Z. Regier, Adam W. Gillespie, Ronald J. Smernik, Johannes Lehman