Substrate Range and Genetic Analysis of Acinetobacter Vanillate Demethylase

An Acinetobacter sp. genetic screen was used to probe structure-function relationships in vanillate demethylase, a two-component monooxygenase. Mutants with null, leaky, and heat-sensitive phenotypes were isolated. Missense mutations tended to be clustered in specific regions, most of which make known contributions to catalytic activity. The vanillate analogs m-anisate, m-toluate, and 4-hydroxy-3,5-dimethylbenzoate are substrates of the enzyme and weakly inhibit the metabolism of vanillate by wild-type Acinetobacter bacteria. PCR mutagenesis of vanAB, followed by selection for strains unable to metabolize vanillate, yielded mutant organisms in which vanillate metabolism is more strongly inhibited by the vanillate analogs. Thus, the procedure opens for investigation amino acid residues that may contribute to the binding of either vanillate or its chemical analogs to wild-type and mutant vanillate demethylases. Selection of phenotypic revertants following PCR mutagenesis gave an indication of the extent to which amino acid substitutions can be tolerated at specified positions. In some cases, only true reversion to the original amino acid was observed. In other examples, a range of amino acid substitutions was tolerated. In one instance, phenotypic reversion failed to produce a protein with the original wild-type sequence. In this example, constraints favoring certain nucleotide substitutions appear to be imposed at the DNA level

Near threshold kaon-kaon interaction in the reactions e+ e- --> K+ K- gamma and e+ e- --> K0 K0bar gamma

Strong interactions between pairs of the K+ K- and K0 K0bar mesons can be studied in radiative decays of phi(1020) mesons. We present a theoretical model of the reactions e+ e- --> phi --> K+ K- gamma and e+ e- --> phi --> K0 K0bar gamma. The K+ K- and K0 K0bar effective mass dependence of the differential cross sections is derived. The total cross sections and the branching fractions for the two radiative phi decays are calculated.Comment: 4 pages, 3 figures, contribution to 15th International Workshop on Meson Physics, Cracow, Poland, 7th - 12th June 201

Strong interaction between kaons in the reactions e+ e- --> K+ K- gamma and e+ e- --> K0 K0bar gamma

A theoretical model of the reactions e+ e- --> K+ K- gamma and e+ e- --> K0 K0bar gamma has been derived. The strong interaction between kaons is taken into account using a general form of the K Kbar scattering amplitude. It is shown that some models formulated in the past are particular cases of the present approach. The formulae for the K Kbar effective mass dependence of the differential cross section as well as for the angular kaon and photon distributions and for the branching fractions of the phi(1020)--> K+ K- gamma and phi(1020)--> K0 K0bar gamma decays have been obtained. We present numerical results for the functions entering into transition amplitudes, K Kbar effective mass distributions, total cross sections, and branching fractions. Finally, the model is generalized to treat other reactions with two pseudoscalar mesons accompanying a photon in the final state.Comment: 17 pages, 7 figure

Biophysically motivated efficient estimation of the spatially isotropic R*2 component from a single gradient‐recalled echo measurement

Purpose To propose and validate an efficient method, based on a biophysically motivated signal model, for removing the orientation‐dependent part of R*2 using a single gradient‐recalled echo (GRE) measurement. Methods The proposed method utilized a temporal second‐order approximation of the hollow‐cylinder‐fiber model, in which the parameter describing the linear signal decay corresponded to the orientation‐independent part of R*2. The estimated parameters were compared to the classical, mono‐exponential decay model for R*2 in a sample of an ex vivo human optic chiasm (OC). The OC was measured at 16 distinct orientations relative to the external magnetic field using GRE at 7T. To show that the proposed signal model can remove the orientation dependence of R*2, it was compared to the established phenomenological method for separating R*2 into orientation‐dependent and ‐independent parts. Results Using the phenomenological method on the classical signal model, the well‐known separation of R*2 into orientation‐dependent and ‐independent parts was verified. For the proposed model, no significant orientation dependence in the linear signal decay parameter was observed. Conclusions Since the proposed second‐order model features orientation‐dependent and ‐independent components at distinct temporal orders, it can be used to remove the orientation dependence of R*2 using only a single GRE measurement

Mapping the human lateral geniculate nucleus and its cytoarchitectonic subdivisions using quantitative MRI

International audienc

More then simply iron: Macro- to microscopic cellular iron distribution in the brain determines MR contrast

Myelin and iron are the major source of MR contrast in the brain. Iron dominates R2*, R2 and QSM in the cortex as well as in subcortical areas and contributes to white matter contrast. To exploit this contrast for cortical parcellation, myeloarchitecture mapping, or iron quantification, significant theoretical and experimental efforts were devoted to the understanding of iron-induced contrast. However, the impact of the cellular and subcellular iron distribution is not well understood. Frequently, it is described by a simple linear dependence of the MRI contrast parameters on iron concentration, largely disregarding the inhomogeneous distribution of iron in the brain. A major reason for this simplification is a lack of quantitative knowledge on the cellular iron distribution. Moreover, the interplay between the microscopic iron distribution and diffusion in creating MR contrast in static de-phasing, motional narrowing or intermediate regime is not fully understood. We set out to address this lack in knowledge and modelling by combining state of the art quantitative 7T MRI with cutting-edge quantitative iron and myelin mapping on post mortem brain samples. Quantitative R2*, R2, R1 and QSM maps were obtained for the human cortex, the subcortical and the deep white matter as well as for brain nuclei before and after de-ironing. Laser Ablation Inductively Coupled Plasma Mass Spectroscopic Imaging (LA ICP MSI) yielded quantitative iron maps with a mesoscopic resolution of 60x120μm. Proton Induced X-ray Emission (PIXE) provided quantitative iron maps with a cellular resolution down to 1μm. MSI and PIXE demonstrated the inhomogenous distribution of iron in both grey and white matter at different spatial scales. In grey matter iron rich fibers, and small (1-3μm) micro-, astro- and oligodendroglia contained most of the iron and were sparsely distributed. In superficial and deep white matter, however, oligodendrocytes somas with the sizes of 5±1.5μm (distance between cells of 20±5μm) and iron rich fibers contained most of the iron. In addition, patches of enhanced iron concentration around small vessels with a typical size of 100-200μm contribute to up to 20% of R2* and QSM and their orientation dependence in white matter. A different contrast mechanism prevailed in brain nuclei where densely packed 20μm large iron loaded neurons dominated the MR contrast. These results provide an important basis for understanding the iron induced MR-contrast and its microstructural underpinnings. Based on these measured microscopic iron distributions and a Gaussian diffusion model we are now in the process of simulating the MR contrast mechanisms in different tissue types

Model of Enterpreneurship and Social-cultural and Market Orientation of Small Business Owners in Poland

In the development of SMEs in Poland crucial meaning is legislation, steadily adapted to EU regulations, especially to the European Charter for Small Enterprises. Research conducted in Poland by many authors provide data for doing so, to confirm the hypothesis that among small businesses a vital role in shaping their work situation did not continue to play the market mechanisms and orientations, but mainly socio-cultural factors.W rozwoju MŚP w Polsce podstawowe znaczenie mają również uregulowania prawne, systematycznie dostosowywane do regulacji unijnych, zwłaszcza zaś do Europejskiej Karty Małych Przedsiębiorstw. Badania prowadzone w Polsce przez wielu autorów dostarczają danych ku temu, by potwierdzić tezę, że wśród drobnych przedsiębiorców decydującą rolę w kształtowaniu ich sytuacji pracy odgrywają nadal nie mechanizmy i orientacje rynkowe, ale przede wszystkim czynniki społeczno-kulturowe

Phonon and Elastic Instabilities in MoC and MoN

We present several results related to the instability of MoC and MoN in the B1 (sodium chloride) structure. These compounds were proposed as potential superconductors with moderately high transition temperatures. We show that the elastic instability in B1-structure MoN, demonstrated several years ago, persists at elevated pressures, thus offering little hope of stabilizing this material without chemical doping. For MoC, another material for which stoichiometric fabrication in the B1-structure has not proven possible, we find that all of the cubic elastic constants are positive, indicating elastic stability. Instead, we find X-point phonon instabilities in MoC (and in MoN as well), further illustrating the rich behavior of carbo-nitride materials. We also present additional electronic structure results for several transition metal (Zr, Nb and Mo) carbo-nitride systems and discuss systematic trends in the properties of these materials. Deviations from strict electron counting dependencies are apparent.Comment: 5 pages and 4 trailing figures. Submitted to PR

Towards a representative reference for MRI-based human axon radius assessment using light microscopy

Non-invasive assessment of axon radii via MRI bears great potential for clinical and neuroscience research as it is a main determinant of the neuronal conduction velocity. However, there is a lack of representative histological reference data at the scale of the cross-section of MRI voxels for validating the MRI-visible, effective radius (reff). Because the current gold standard stems from neuroanatomical studies designed to estimate the bulk-determined arithmetic mean radius (rarith) on small ensembles of axons, it is unsuited to estimate the tail-weighted reff. We propose CNN-based segmentation on high-resolution, large-scale light microscopy (lsLM) data to generate a representative reference for reff. In a human corpus callosum, we assessed estimation accuracy and bias of rarith and reff. Furthermore, we investigated whether mapping anatomy-related variation of rarith and reff is confounded by low-frequency variation of the image intensity, e.g., due to staining heterogeneity. Finally, we analyzed the error due to outstandingly large axons in reff. Compared to rarith, reff was estimated with higher accuracy (maximum normalized-root-mean-square-error of reff: 8.5 %; rarith: 19.5 %) and lower bias (maximum absolute normalized-mean-bias-error of reff: 4.8 %; rarith: 13.4 %). While rarith was confounded by variation of the image intensity, variation of reff seemed anatomy-related. The largest axons contributed between 0.8 % and 2.9 % to reff. In conclusion, the proposed method is a step towards representatively estimating reff at MRI voxel resolution. Further investigations are required to assess generalization to other brains and brain areas with different axon radii distributions