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991.
Effects of purification on the crystallization of lysozyme 总被引:2,自引:0,他引:2
Felecia L. Ewing Elizabeth L. Forsythe Mark van der Woerd Marc L. Pusey 《Journal of Crystal Growth》1996,160(3-4):389-397
We have additionally purified a commercial lysozyme preparation by cation exchange chromatography, followed by recrystallization. This material is 99.96% pure with respect to macromolecular impurities. At basic pH, the purified lysozyme gave only tetragonal crystals at 20°C. Protein used directly from the bottle, prepared by dialysis against distilled water, or which did not bind to the cation exchange column had considerably altered crystallization behavior. Lysozyme which did not bind to the cation exchange column was subsequently purified by size exclusion chromatography. This material gave predominately bundles of rod-shaped crystals with some small tetragonal crystals at lower pHs. The origin of the bundled rod habit was postulated to be a thermally dependent tetragonal ↔ orthorhombic change in the protein structure. This was subsequently ruled out on the basis of crystallization behavior and growth rate experiments. This suggests that heterogeneous forms of lysozyme may be responsible. These results demonstrate three classes of impurities: (1) small molecules, which may be removed by dialysis; (2) macromolecules, which are removable by chromatographic techniques; and (3) heterogeneous forms of the protein, which can be removed in this case by cation exchange chromatography. Of these, heterogeneous forms of the lysozyme apparently have the greatest affect on its crystallization behavior. 相似文献
992.
Crystals of the 3-acetoxy derivative of -amyrin are monoclinic, space groupP21 witha = 8.021(1),b = 11.474(1),c = 15.564(2) Å, and = 100.496(3) °. Crystals of the 3-benzoxy derivative are orthorhombic, space groupP212121, witha = 6.752(1),b = 12.974(1), andc = 36.664(3) Å. Both structures have been solved by direct methods and refined by full-matrix least-squares, using data collected on an automated four-circle diffractometer. The final residuals for the acetoxy and benzoxy structures are 0.055 (2274 significant independent reflections) and 0.152 (1220 significant independent reflections) respectively. The geometry of the -amyrin skeleton in both structures is similar to that found in other triterpene structures containing a system of five condensed six-membered rings. RingC has a C(8)-sofa conformation due to the presence of the double bond at C(12)-C(13) whereas in the remaining rings thechair conformation predominates. 相似文献
993.
We report a simple and highly stereocontrolled strategy toward the total synthesis of isoprostanes based on a bicyclic alpha,beta-epoxy ketone intermediate 6. Bicyclo[3.3.0]octene scaffold permitted stereodirection of reagents allowing stereoselective epoxidation, diastereoselective ketone reduction, and regioselective epoxide opening otherwise not accessible with a simple cyclopentene framework. 相似文献
994.
In this article, we will study plane curves of a certain degreed with three or four total inflection points. In particular,we will study their image in the moduli spaces. Also a resulton curves with five total inflection points is included. 相似文献
995.
996.
Moors SL Jonckheer A De Maeyer M Engelborghs Y Ceulemans A 《Current protein & peptide science》2008,9(5):427-446
We discuss the dynamics of tryptophan rotamers in the context of the non-exponential fluorescence decay in proteins. The central question is: how does the ground-state conformational heterogeneity influence the time evolution of tryptophan fluorescence? This problem is examined here from the theoretical perspective. Three methods at different levels of theory, and with different scopes and computational requirements are reviewed. The Dead-end elimination method is limited to side-chain dynamics and provides an efficient way to detect the stable tryptophan rotamers in a protein. Its application to the study of heterogeneous emission characteristics is illustrated. Molecular dynamics is aimed at the full phase space of the macromolecule in solution, but must rely on classical force fields and laws of evolution. We examine to what extent the molecular mechanics paradigm yields sufficiently accurate thermodynamic results, and what are the possible kinetic implications. Finally Quantum Chemistry is the only theoretical method that allows a direct assessment of the excited states. It is necessarily restricted to small molecular systems, and thus must be used in a hybrid combination with classical methods and electrostatic models. So far understanding of the emitting state has greatly progressed as a result of these calculations, but the actual treatment of the photophysical decay processes at the quantum level has not yet really started. 相似文献
997.
Polyunsaturated fatty acids (PUFAs) are important constituents in all organisms. They fulfil many functions, ranging from modulating the structure of membranes to acting as precursors of physiologically important molecules, such as the prostaglandins, which for a long time were the most prominent cyclic PUFA metabolites. However, since the beginning of the 1990s a large variety of cyclic metabolites have been discovered that form under autoxidative conditions in vivo to a much larger extent than do prostaglandins. These compounds--isoprostanes, neuroprostanes, phytoprostanes, and isofurans--proved subsequently to be ubiquitous in nature. They display a wide range of biological activities, and isoprostanes have become the currently most reliable indicators of oxidative stress in humans. In a relatively short time, the structural variety, properties, and applications of the autoxidatively formed cyclic PUFA derivatives have been uncovered. 相似文献
998.
Deschamps M Fayon F Hiet J Ferru G Derieppe M Pellerin N Massiot D 《Physical chemistry chemical physics : PCCP》2008,10(9):1298-1303
Scalar couplings, recoupled or full dipolar interactions can be used to characterize multinuclear structural molecular motifs in solids, by counting the neighbouring spins in solid-state NMR, opening new ways for the differentiation of overlapping spectral responses which is a limiting factor in many high resolution experiments carried out on disordered systems. 相似文献
999.
NiFe hydrogenases are unique enzymes that catalyze the H+/H2 interconversion with remarkable efficiency. The determination of the tridimensional structure of their active site (a sulfur-rich dinuclear nickel-iron cluster with diatomic cyanide and carbonyl ligands) has stimulated the synthesis of a variety of nickel-based complexes as potential electrocatalysts for hydrogen production. These catalysts may provide an adequate alternative to platinum. This paper gives an historical perspective of this biomimetic structural approach and then focusses on recently reported bio-inspired functional mimics displaying electrocatalytic activity for hydrogen production. 相似文献
1000.
Anderson KE Hirschmann MM Siepmann JI 《The journal of physical chemistry. B》2008,112(41):13005-13014
Monte Carlo simulations were used to investigate the phase behavior of hydrated liquid silica as a function of temperature and overall water mole fraction, x w. Simulations using the Feuston-Garofalini potential were performed in the isobaric-isothermal ensemble at p = 1 GPa for 15 temperatures (2000 < or = T < or = 9000 K) and 25 compositions (0.0 < or = x w < or = 0.4). The unusual volume minimum exhibited by tetrahedrally coordinated liquid silica is found to persist up to x w approximately 0.267, although the temperature of the volume minimum decreases with increasing water content. Structural properties of the pure and hydrated systems are compared and the addition of water to liquid silica disrupts the silica network more dramatically than temperature alone. The simulations yield very low concentrations of molecular water, e.g. only about 1.2% of the oxygen atoms are bound to exactly two hydrogen atoms at x w = 0.4 and T = 3000 K. 相似文献