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991.
According to the hypothesis that the chirality of molecule hosts is a cause of their enantioselectivity, the chirality of para-substituted calix[4]arenes was analyzed quantitatively. The relationship between types of para-substituents and the dissymmetry of the 2D (two-dimensional) entrance into the cavity and the whole 3D (three-dimensional) cavity of calix[4]arenes was studied by means of the enantiomer dissimilarity factor (EDF) method for quantitative evaluation of molecular chirality. The design of the most chiral, and probably enantioselective, para-substituted calix[4]arenes was planned such that all four substituents should be different and the two largest should be near each other (adjacent). It was, on the other hand, shown that the 2D chiral entrance determines chirality of the whole 3D structures of these molecules. This phenomenon is interpreted as an example of the chirality transition from 2D into 3D space.Electronic Supplementary Material available. 相似文献
992.
Victor Mu?oz Robles Jean-Didier Maréchal Amel Bahloul Marie-Agnès Sari Jean-Pierre Mahy Béatrice Golinelli-Pimpaneau 《PloS one》2012,7(12)
We report the crystal structures at 2.05 and 2.45 Å resolution of two antibodies, 13G10 and 14H7, directed against an iron(III)-αααβ-carboxyphenylporphyrin, which display some peroxidase activity. Although these two antibodies differ by only one amino acid in their variable λ-light chain and display 86% sequence identity in their variable heavy chain, their complementary determining regions (CDR) CDRH1 and CDRH3 adopt very different conformations. The presence of Met or Leu residues at positions preceding residue H101 in CDRH3 in 13G10 and 14H7, respectively, yields to shallow combining sites pockets with different shapes that are mainly hydrophobic. The hapten and other carboxyphenyl-derivatized iron(III)-porphyrins have been modeled in the active sites of both antibodies using protein ligand docking with the program GOLD. The hapten is maintained in the antibody pockets of 13G10 and 14H7 by a strong network of hydrogen bonds with two or three carboxylates of the carboxyphenyl substituents of the porphyrin, respectively, as well as numerous stacking and van der Waals interactions with the very hydrophobic CDRH3. However, no amino acid residue was found to chelate the iron. Modeling also allows us to rationalize the recognition of alternative porphyrinic cofactors by the 13G10 and 14H7 antibodies and the effect of imidazole binding on the peroxidase activity of the 13G10/porphyrin complexes. 相似文献
993.
994.
Marcio Voloch Michael R. Ladisch Victor W. Rodwell George T. Tsao 《Biotechnology and bioengineering》1981,23(6):1289-1296
Fermentation of xylose by Klebsiella pneumoniae (ATCC 8724) producers meso and nonmeso 2,3-butaneodiol. The enzyme Kinetic of 2,3-butanediol stereoisomer formation from acetone is currently under study in our laboratory. Modeling of these kinetics requires resolution of meso and racemic 2,3-butanediol and positive identification of these resolved components. We report their resolution by aqueous liquid chromatography on both an analytical and a preparative scale. The resolved stereoisomer were identified by a combination of gas chromatography, gas chromatography/mass spectroscopy, 13C-NMR spectroscopy, optical activity, and, melting points of the m-dinitrobenzoyl eaters of meso and racemic 2,3-butanediol. An aqueous liquid chromatographic technique for resolving and qualifying major components of a butanediol fermentation mixture in 40 min is presented. 相似文献
995.
996.
997.
Microparticles (MPs) are small membrane fragments shed from normal as well as activated, apoptotic or injured cells. Emerging evidence implicates MPs as a causal and/or contributing factor in altering normal vascular cell phenotype through initiation of proinflammatory signal transduction events and paracrine delivery of proteins, mRNA and miRNA. However, little is known regarding the mechanism by which MPs influence these events. Caveolae are important membrane microdomains that function as centers of signal transduction and endocytosis. Here, we tested the concept that the MP-induced pro-inflammatory phenotype shift in endothelial cells (ECs) depends on caveolae. Consistent with previous reports, MP challenge activated ECs as evidenced by upregulation of intracellular adhesion molecule-1 (ICAM-1) expression. ICAM-1 upregulation was mediated by activation of NF-κB, Poly [ADP-ribose] polymerase 1 (PARP-1) and the epidermal growth factor receptor (EGFR). This response was absent in ECs lacking caveolin-1/caveolae. To test whether caveolae-mediated endocytosis, a dynamin-2 dependent process, is a feature of the proinflammatory response, EC’s were pretreated with the dynamin-2 inhibitor dynasore. Similar to observations in cells lacking caveolin-1, inhibition of endocytosis significantly attenuated MPs effects including, EGFR phosphorylation, activation of NF-κB and upregulation of ICAM-1 expression. Thus, our results indicate that caveolae play a role in mediating the pro-inflammatory signaling pathways which lead to EC activation in response to MPs. 相似文献
998.
We have studied the concentration and ionic strength dependence of the fiber-reorientation transition in T2L bacteriophage, using sedimentation velocity and quasielastic light scattering diffusion measurements. High-salt and low-phage concentration favor the form with fibers extended. The equilibrium between the two forms is dependent on the phage Concentration. This behavior is unexpected for a reaction that is apparently unimolecular with respect to phage, and attests to the strong increase in excluded volume and other interactions accompanying fiber extension. The fiber-extended form has anomalously high diffusion coefficient and low molecular weight according to the Svedberg equation. 相似文献
999.
1000.