Enzyme activity in bicontinuous microemulsions

The thesis deals with enzymatic catalysis in bicontinuous microemulsions, which consist of a dynamic network of oil and water domains separated by a monolayer of surfactant molecules, i.e. the interfacial layer. Hence, a microemulsion with the composition buffer – n-octane – nonionic surfactant was tested as a reaction medium for enzyme-catalysed reactions with the emphasis on the conversion of hydrophobic substrates, which are difficult to convert in aqueous buffer solutions. The first part of the thesis focuses on the activity of the lipase B from Candida antarctica (CalB) in bicontinuous microemulsions. First, the optimum reaction conditions determined by temperature, pH and ionic strength were evaluated. Second, it was found that CalB concentrations which showed fast adsorption at an oil-water interface also displayed fast reaction rates. Additionally, no saturation was found for substrate concentrations up to 40 mM of p-nitrophenyl laurate, which according to Michaelis-Menten suggests a Km >> 40 mM. Third, the composition of the interfacial layer had a distinct influence on CalB activity, e.g. the presence of sugar surfactants (b-C10G1) or phospholipids (DOPC) enhanced or decreased CalB activity, respectively. The second part of the thesis describes the activity of the squalene-hopene cyclase from Alicyclobacillus acidocaldarius (Aac SHC) converting its natural substrate squalene in bicontinuous microemulsions. The Aac SHC activity studies revealed a linear dependence on enzyme concentration and a hyperbolic curve for the substrate concentration, with a saturation of Aac SHC at substrate concentrations above 20 mM. The composition of the interfacial layer was found to have neither a significant influence on the activity nor on the conformation of Aac SHC. In summary, good turnover rates were achieved for interfacially-active enzymes (CalB) due to enhanced enzyme-substrate contact at the interfacial layer. For water-soluble enzymes (Aac SHC), a distinctly enhanced selectivity was discovered, although no faster reaction rate was found. The main difference in the catalytic turnover was explained by the adsorption of CalB at the interfacial layer, whereas Aac SHC stays in the aqueous phase of the microemulsion. To conclude, bicontinuous microemulsions were suitable for enzymatic catalysis and are thus interesting in terms of reaction medium engineering to optimise biocatalytic processes

Root hydraulic conductivity measured by pressure clamp is substantially affected by internal unstirred layers

Using the root pressure probe in the pressure clamping (PC) mode, the impact of internal unstirred layers (USLs) was quantified for young corn roots, both in experiments and in computer simulations applying the convection/diffusion model of Knipfer et al. In the experiments, water flows (JVrs) during PC were analysed in great detail, showing that JVrs (and the apparent root hydraulic conductivity) were high during early stages of PC and declined rapidly during the first 80 s of clamping to a steady-state value of 40–30% of the original. The comparison of experimental results with simulations showed that, during PC, internal USLs at the inner surface of the endodermis substantially modify the overall force driving the water. As a consequence, JVr and Lpr were inhibited. Effects of internal USLs were minimized when using the pressure relaxation mode, when internal USLs had not yet developed. Additional stop-clamp experiments and experiments where the endodermis was punctured to reduce the effect of internal USLs verified the existence of internal USLs during PC. Data indicated that the role of pressure propagation along the root xylem for both PC and pressure relaxation modes should be small, as should the effects of filling of the capacities during root pressure probe experiments, which are discussed as an alternative model. The results supported the idea that concentration polarization effects at the endodermis (internal USLs) cause a serious problem whenever relatively large amounts of water (xylem sap) are radially moved across the root, such as during PC or when using the high-pressure flow meter technique

Permeability of Iris germanica’s multiseriate exodermis to water, NaCl, and ethanol

The exodermis of Iris germanica roots is multiseriate. Its outermost layer matures first with typical Casparian bands and suberin lamellae. But as subsequent layers mature, the Casparian band extends into the tangential and anticlinal walls of their cells. Compared with roots in which the endodermis represents the major transport barrier, the multiseriate exodermis (MEX) was expected to reduce markedly radial water and solute transport. To test this idea, precocious maturation of the exodermis was induced with a humid air gap inside a hydroponic chamber. Hydraulic conductivity (Lppc) was measured on completely submerged roots (with an immature exodermis) and on air-gap-exposed root regions (with two mature exodermal layers) using a pressure chamber. Compared with regions of roots with no mature exodermal layers, the mature MEX reduced Lppc from 8.5×10−8 to 3.9×10−8 m s−1 MPa−1. Puncturing the MEX increased Lppc to 19×10−8 m s−1 MPa−1, indicating that this layer constituted a substantial hydraulic resistance within the root (75% of the total). Alternatively, a root pressure probe was used to produce pressure transients from which hydraulic conductivity was determined, but this device measured mainly flow through the endodermis in these wide-diameter roots. The permeability of roots to NaCl and ethanol was also reduced in the presence of two mature MEX layers. The data are discussed in terms of the validity of current root models and in terms of a potential role for I. germanica MEX during conditions of drought and salt stress

Quantum Nature of Light Measured With a Single Detector

We realized the most fundamental quantum optical experiment to prove the non-classical character of light: Only a single quantum emitter and a single superconducting nanowire detector were used. A particular appeal of our experiment is its elegance and simplicity. Yet its results unambiguously enforce a quantum theory for light. Previous experiments relied on more complex setups, such as the Hanbury-Brown-Twiss configuration, where a beam splitter directs light to two photodetectors, giving the false impression that the beam splitter is required. Our work results in a major simplification of the widely used photon-correlation techniques with applications ranging from quantum information processing to single-molecule detection.Comment: 7 page

Englischlernen von Menschen mit (geistiger) Behinderung aus Nutzersicht – eine qualitative Pilotstudie zum Einfluss des Bildungsinhalts Englisch auf Selbstbild, Teilhabe, Bildungsanspruch und Lernverhalten

Die vorliegende Studie untersucht mögliche Auswirkungen des Englischlernens von Menschen mit geistiger Behinderung aus Nutzersicht. Befragt wurden 33 Personen zwischen 12 und 63 Jahren, die in unterschiedlichen institutionellen Kontexten Englisch als Fremdsprache lernen. Methodisch wurde hierzu ein eigener Interviewleitfaden entwickelt. Die Auswertung der transkribierten Daten erfolgte über die Qualitative Inhaltsanalyse sowie computergestützte Datenauswertung. Die Ergebnisse belegen, dass Englischlernen für die Befragten eine enorme Bedeutung einnimmt. Es wurden förderliche Auswirkungen auf Aspekte ihres Selbstbildes, ihrer individuellen Teilhabemöglichkeiten sowie ihres Lernverhaltens festgestellt. Hieraus ergeben sich bildungspolitische sowie praxisbezogene Implikationen, die Englisch als verankertes, flächendeckendes Bildungsangebot für alle Menschen in jeder Lebensphase fordern

Revealing Hidden Potentials of the q-Space Signal in Breast Cancer

Mammography screening for early detection of breast lesions currently suffers from high amounts of false positive findings, which result in unnecessary invasive biopsies. Diffusion-weighted MR images (DWI) can help to reduce many of these false-positive findings prior to biopsy. Current approaches estimate tissue properties by means of quantitative parameters taken from generative, biophysical models fit to the q-space encoded signal under certain assumptions regarding noise and spatial homogeneity. This process is prone to fitting instability and partial information loss due to model simplicity. We reveal unexplored potentials of the signal by integrating all data processing components into a convolutional neural network (CNN) architecture that is designed to propagate clinical target information down to the raw input images. This approach enables simultaneous and target-specific optimization of image normalization, signal exploitation, global representation learning and classification. Using a multicentric data set of 222 patients, we demonstrate that our approach significantly improves clinical decision making with respect to the current state of the art.Comment: Accepted conference paper at MICCAI 201

Gating of aqùaporins by light and reactive oxygen species in leaf parenchyma cells of the midrib of Zea mays

Changes of the water permeability aqùaporin (AQP) activity of leaf cells were investigated in response to different light regimes (low versus high). Using a cell pressure probe, hydraulic properties (half-time of water exchange, T1/2 ∞ 1/water permeability) of parenchyma cells in the midrib tissue of maize (Zea mays L.) leaves have been measured. A new perfusion technique was applied to excised leaves to keep turgor constant and to modify the environment around cells by perfusing solutions using a pressure chamber. In response to low light (LL) of 200 μmol m−2 s−1, T1/2 decreased during the perfusion of a control solution of 0.5 mM CaCl2 by a factor of two. This was in line with earlier results from leaf cells of intact maize plants at a constant turgor. In contrast, high light (HL) at intensities of 800 μmol m−2 s−1 and 1800 μmol m−2 s−1 increased the T1/2 in two-thirds of cells by factors of 14 and 35, respectively. The effects of HL on T1/2 were similar to those caused by H2O2 treatment in the presence of Fe2+, which produced ·OH (Fenton reaction; reversible oxidative gating of aquaporins). Treatments with 20 mM H2O2 following Fe2+ pre-treatments increased the T1/2 by a factor of 30. Those increased T1/2 values could be partly recovered, either when the perfusion solution was changed back to the control solutuion or when LL was applied. 3mM of the antioxidant glutathione also reversed the effects of HL. The data suggest that HL could induce reactive oxygen species (ROS) such as ·OH, and they affected water relations. The results provide evidence that the varying light climate adjusts water flow at the cell level; that is, water flow is maximized at a certain light intensity and then reduced again by HL. Light effects are discussed in terms of an oxidative gating of aquaporins by ROS