A Proton Magnetic Resonance Study of the Association of Lysozyme with Monosaccharide Inhibitors

It has been shown that the acetamido methyl protons of N-acetyl-d-glucosamine undergo a chemical shift to higher fields in their proton magnetic resonance spectrum when the inhibitor is bound to lysozyme. The observed chemical shift in the presence of the enzyme is different for the agr- and ß-anomeric forms of 2-acetamido-2-deoxy-d-glucopyranose indicating either a difference in the affinity of the anomeric forms for lysozyme or different magnetic environments for the methyl protons in their enzyme-bound state. That the agr- and ß-anomeric forms of GlcAc bind to lysozyme in a competitive fashion was indicated by observing the proton magnetic resonance spectra in the presence of 2-acetamido-d3-2-deoxy-agr-d-glucopyranose. The methyl glycosides, methyl-agr-GlcAc and methyl-ß-GlcAc, were also shown to bind competitively with both anomers of GlcAc. Quantitative analysis of the chemical shift data observed for the association of GlcAc with lysozyme was complicated by the mutarotation of GlcAc between its agr- and ß-anomeric forms. However, in the case of the methyl glucosides, where the conformation of each anomer is frozen, it was possible to analyze the chemical shift data in a straightforward manner, and the dissociation constant as well as the chemical shift of the acetamido methyl protons of the enzyme-inhibitor complex was determined for both anomers. The results indicate that the two anomers of methyl-GlcAc bind to lysozyme with slightly different affinities but that the acetamido methyl groups of both anomers experience identical magnetic environments in the enzyme-inhibitor complex

Corporate Governance and the Home Bias

This paper shows that there is a close relation between corporate governance and the portfolios held by investors. Most firms in countries with poor investor protection are controlled by large shareholders, so that only a fraction of the shares issued by firms in these countries can be freely traded and held by portfolio investors. We show that the prevalence of closely-held firms in most countries helps explain why these countries exhibit a home bias in share holdings and why U.S. investors underweight foreign countries in their portfolios. We construct an estimate of the world portfolio of shares available to investors who are not controlling shareholders (the world float portfolio). The world float portfolio differs sharply from the world market portfolio. In regression explaining the portfolio weights of U.S. investors, the world float portfolio has a positive significant coefficient but the world market portfolio has no additional explanatory power. This result holds when we control for country characteristics. An analysis of foreign investor holdings at the firm level for Sweden confirms the importance of the float portfolio as a determinant of these holdings.World float portfolio; Portfolio choice; Closely held shares

New analysis method of the halo phenomenon in finite many-fermion systems. First applications to medium-mass atomic nuclei

A new analysis method to investigate halos in finite many-fermion systems is designed, as existing characterization methods are proven to be incomplete/inaccurate. A decomposition of the internal wave-function of the {$N$-body} system in terms of overlap functions allows a model-independent analysis of medium-range and asymptotic properties of the internal one-body density. The existence of a spatially decorrelated region in the density profile is related to the existence of three typical energy scales in the excitation spectrum of the {$(N-1)$-body} system. A series of model-independent measures, taking the internal density as the only input, are introduced. The new measures allow a quantification of the potential halo in terms of the average number of fermions participating to it and of its impact on the system extension. Those new "halo factors" are validated through simulations and applied to results obtained through energy density functional calculations of medium-mass nuclei. Performing spherical Hartree-Fock-Bogoliubov calculations with state-of-the-art Skyrme plus pairing functionals, a collective halo is predicted in drip-line Cr isotopes, whereas no such effect is seen in Sn isotopes.Comment: 27 Pages, 29 Figures. Accepted for publication in Phys. Rev. C back-to-back with second part (arXiv:0711.1275

Structural and chemical requirements for histidine phosphorylation by the chemotaxis kinase CheA

The CheA histidine kinase initiates the signal transduction pathway of bacterial chemotaxis by autophosphorylating a conserved histidine on its phosphotransferase domain (P1). Site-directed mutations of neighboring conserved P1 residues (Glu-67, Lys-48, and His-64) show that a hydrogen-bonding network controls the reactivity of the phospho-accepting His (His-45) in Thermotoga maritima CheA. In particular, the conservative mutation E67Q dramatically reduces phospho-transfer to P1 without significantly affecting the affinity of P1 for the CheA ATP-binding domain. High resolution crystallographic studies revealed that although all mutants disrupt the hydrogen-bonding network to varying degrees, none affect the conformation of His-45. N-15-NMR chemical shift studies instead showed that Glu-67 functions to stabilize the unfavored (NH)-H-delta 1 tautomer of His-45, thereby rendering the N-epsilon 2 imidazole unprotonated and well positioned for accepting the ATP phosphoryl group

Halo phenomenon in finite many-fermion systems. Atom-positron complexes and large-scale study of atomic nuclei

The analysis method proposed in Ref. \cite{rotival07a} is applied to characterize halo properties in finite many-fermion systems. First, the versatility of the method is highlighted by applying it to light and medium-mass nuclei as well as to atom-positron and ion-positronium complexes. Second, the dependence of nuclear halo properties on the characteristics of the energy density functional used in self-consistent Hartree-Fock-Bogoliubov calculations is studied. It is found that (a) the low-density behavior of the pairing functional and the regularization/renormalization scheme must be chosen coherently and with care to provide meaningful predictions, (b) the impact of pairing correlations on halo properties is significant and is the result of two competing effects, (c) the detailed characteristics of the pairing functional has however only little importance, (d) halo properties depend significantly on any ingredient of the energy density functional that influences the location of single-particle levels; i.e. the effective mass, the tensor terms and the saturation density of nuclear matter. The latter dependencies give insights to how experimental data on medium-mass drip-line nuclei can be used in the distant future to constrain some characteristics of the nuclear energy density functional. Last but not least, large scale predictions of halos among all spherical even-even nuclei are performed using specific sets of particle-hole and particle-particle energy functionals. It is shown that halos in the ground state of medium-mass nuclei will only be found at the very limit of neutron stability and for a limited number of elements.Comment: 24 Pages, 32 Figures. Accepted for publication in Phys. Rev. C back-to back with first part (nucl-th/0702050

The geological setting of Carboniferous magmatism in the proto-Andean margin of Gondwana, Sierra Pampeanas, Argentina

Fil: Dahlquist, J. A. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina.Fil: Dahlquist, J. A. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones en Ciencias de la Tierra; Argentina.Fil: Basei, M. Universida de de Sao Paulo. Instituto de Geociencias; Brasil.Fil: Alasino, P. H. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina.Fil: Alasino, P. H. Universidad Nacional de la Rioja. INGeReN-CENIIT; Argentina.Fil: Alasino, P. H. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja; Argentina.Fil: Campos, M. Universidade de Sao Paulo. Instituto de Geociencias; Brasil.Fil: Casquet, C. Universidad Complutense. Departamento de Petrología y Geoquímica; España.Our petrogenetic understanding of the Carboniferous granites of the Sierras Pampeanas has improved in recent years, but their geodynamic setting is still not well constrained. Domeier and Torsvik (2014) affirm that there is no documented and unambiguous evidence of an active margin in the proto-Andean margin of Gondwana before the late Carboniferous (~ 320 Ma).Fil: Dahlquist, J. A. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina.Fil: Dahlquist, J. A. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones en Ciencias de la Tierra; Argentina.Fil: Basei, M. Universida de de Sao Paulo. Instituto de Geociencias; Brasil.Fil: Alasino, P. H. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina.Fil: Alasino, P. H. Universidad Nacional de la Rioja. INGeReN-CENIIT; Argentina.Fil: Alasino, P. H. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja; Argentina.Fil: Campos, M. Universidade de Sao Paulo. Instituto de Geociencias; Brasil.Fil: Casquet, C. Universidad Complutense. Departamento de Petrología y Geoquímica; España.Geoquímica y Geofísic

Domain wall interacting with a black hole: A new example of critical phenomena

We study a simple system that comprises all main features of critical gravitational collapse, originally discovered by Choptuik and discussed in many subsequent publications. These features include universality of phenomena, mass-scaling relations, self-similarity, symmetry between super-critical and sub-critical solutions, etc. The system we consider is a stationary membrane (representing a domain wall) in a static gravitational field of a black hole. For a membrane that spreads to infinity, the induced 2+1 geometry is asymptotically flat. Besides solutions with Minkowski topology there exists also solutions with the induced metric and topology of a 2+1 dimensional black hole. By changing boundary conditions at infinity, one finds that there is a transition between these two families. This transition is critical and it possesses all the above-mentioned properties of critical gravitational collapse. It is remarkable that characteristics of this transition can be obtained analytically. In particular, we find exact analytical expressions for scaling exponents and wiggle-periods. Our results imply that black hole formation as a critical phenomenon is far more general than one might expect.Comment: 23 pages, 5 postscript figures include