Thermodynamic considerations in the analysis of phase stability: The role of interfacial equilibrium in the determination of phase diagrams by X-ray microanalytical techniques

1987 ◽  
Vol 8 (4) ◽  
pp. 308-322 ◽  
Author(s):  
A. D. Romig
Keyword(s):  
Phase Diagrams ◽  
Phase Stability ◽  
X Ray

scholarly journals Crystallization and X-ray diffraction data analysis of human deoxyhaemoglobin A0 fully stripped of any anions

1999 ◽  
Vol 55 (11) ◽  
pp. 1914-1916 ◽  
Author(s):  
F. A. V. Seixas ◽  
W. F. de Azevedo ◽  
M. F. Colombo
Keyword(s):  
Diffraction Data ◽  
Oxygen Affinity ◽  
X Ray Diffraction ◽  
Structural Explanation ◽  
Human Haemoglobin ◽  
X Ray ◽  
High Resolution Structure ◽  
Allosteric Properties

In this work, initial crystallographic studies of human haemoglobin (Hb) crystallized in isoionic and oxygen-free PEG solution are presented. Under these conditions, functional measurements of the O2-linked binding of water molecules and release of protons have evidenced that Hb assumes an unforeseen new allosteric conformation. The determination of the high-resolution structure of the crystal of human deoxy-Hb fully stripped of anions may provide a structural explanation for the role of anions in the allosteric properties of Hb and, particularly, for the influence of chloride on the Bohr effect, the mechanism by which Hb oxygen affinity is regulated by pH. X-ray diffraction data were collected to 1.87 Å resolution using a synchrotron-radiation source. Crystals belong to the space group P21212 and preliminary analysis revealed the presence of one tetramer in the asymmetric unit. The structure is currently being refined using maximum-likelihood protocols.

scholarly journals Role of Computational Methods in Going beyond X-ray Crystallography to Explore Protein Structure and Dynamics

2018 ◽  
Vol 19 (11) ◽  
pp. 3401 ◽  
Author(s):  
Ashutosh Srivastava ◽  
Tetsuro Nagai ◽  
Arpita Srivastava ◽  
Osamu Miyashita ◽  
Florence Tama
Keyword(s):  
Protein Dynamics ◽  
Computational Methods ◽  
Protein Structures ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
X Ray ◽  
X Ray Crystallography ◽  
Insight Into

Protein structural biology came a long way since the determination of the first three-dimensional structure of myoglobin about six decades ago. Across this period, X-ray crystallography was the most important experimental method for gaining atomic-resolution insight into protein structures. However, as the role of dynamics gained importance in the function of proteins, the limitations of X-ray crystallography in not being able to capture dynamics came to the forefront. Computational methods proved to be immensely successful in understanding protein dynamics in solution, and they continue to improve in terms of both the scale and the types of systems that can be studied. In this review, we briefly discuss the limitations of X-ray crystallography in studying protein dynamics, and then provide an overview of different computational methods that are instrumental in understanding the dynamics of proteins and biomacromolecular complexes.

scholarly journals New insights into the mechanism of substrates trafficking in Glyoxylate/Hydroxypyruvate reductases

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
Louise Lassalle ◽  
Sylvain Engilberge ◽  
Dominique Madern ◽  
Pierre Vauclare ◽  
Bruno Franzetti ◽  
...  
Keyword(s):  
Renal Failure ◽  
Active Site ◽  
Ternary Complex ◽  
Substrate Recognition ◽  
Binding Mode ◽  
X Ray ◽  
Hyperoxaluria Type

Abstract Glyoxylate accumulation within cells is highly toxic. In humans, it is associated with hyperoxaluria type 2 (PH2) leading to renal failure. The glyoxylate content within cells is regulated by the NADPH/NADH dependent glyoxylate/hydroxypyruvate reductases (GRHPR). These are highly conserved enzymes with a dual activity as they are able to reduce glyoxylate to glycolate and to convert hydroxypyruvate into D-glycerate. Despite the determination of high-resolution X-ray structures, the substrate recognition mode of this class of enzymes remains unclear. We determined the structure at 2.0 Å resolution of a thermostable GRHPR from Archaea as a ternary complex in the presence of D-glycerate and NADPH. This shows a binding mode conserved between human and archeal enzymes. We also determined the first structure of GRHPR in presence of glyoxylate at 1.40 Å resolution. This revealed the pivotal role of Leu53 and Trp138 in substrate trafficking. These residues act as gatekeepers at the entrance of a tunnel connecting the active site to protein surface. Taken together, these results allowed us to propose a general model for GRHPR mode of action.

Determination of the Width of the Single Phase Stability Field of Nickel Titanate Spinel

1991 ◽  
Vol 237 ◽  
Author(s):  
Ian M. Anderson ◽  
C. Barry Carter
Keyword(s):  
Phase Stability ◽  
Single Phase ◽  
Narrow Range ◽  
Spinel Phase ◽  
Stability Field ◽  
Diffusion Couples ◽  
Temperature Dependent ◽  
X Ray ◽  
Nickel Titanate

ABSTRACTThe width of the single-phase stability field of nickel titanate spinel (Ni2(1+x)Ti1−xO4) has been determined in order to resolve an ambiguity in the analysis of the microstructure of equilibrated and quenched spinel-containing specimens. Bulk polycrystalline diffusion couples of the constituent oxides, NiO and NiTiO3, have been prepared at several reaction temperatures between 1400°C and 1550°C. The microstructure of the reaction layers of slow-cooled specimens has been examined by SEM and the composition has been mapped using x-ray microanalysis. It is concluded that the nickel titanate spinel phase has a narrow range of stability, and that the stoichiometry of the spinel is temperature dependent. The microstructure of equilibrated and quenched specimens is discussed in light of these findings.

The Determination of Zinc Oxide in Rubber Vulcanizates by X-Ray Diffraction

1960 ◽  
Vol 33 (3) ◽  
pp. 890-898
Author(s):  
Stephen H. Laning ◽  
Melvin P. Wagner ◽  
John W. Sellers
Keyword(s):  
Zinc Oxide ◽  
Quantitative Analysis ◽  
Analytical Method ◽  
Direct Determination ◽  
Zinc Stearate ◽  
Photographic Film ◽  
Reaction Products ◽  
X Ray

Abstract Zinc oxide is a necessary component in most accelerator-sulfur vulcanization systems. While it is not an accelerator, its presence leads to increased modulus, i.e., tighter cures. The manner in which it can effect this better cure is not completely clear. Some insight into the role of zinc oxide has been gained through the analysis of the vulcanizate for reaction products of zinc, such as zinc stearate, the zinc salts of the accelerators, and zinc sulfide. However, these products may not account for all of the zinc oxide which has reacted. An analytical method for the direct determination of unreacted zinc oxide in vulcanizates was therefore needed. The determination of zinc oxide in rubber vulcanizates has received scant attention. Wet-chemical techniques for analysis of the sample after ashing provide only the total amount of zinc from which the amount of unreacted zinc oxide cannot be determined. Endter has reported the use of the Debye-Scherrer x-ray technique for the identification of zinc oxide in rubber samples. While similar to the method developed in this laboratory, Endter employed photographic film for recording the diffraction pattern, and special sample preparation was required to accommodate the photographic technique. This method was satisfactory for qualitative identification of zinc oxide, but was difficult to use for quantitative analysis. Subsequent to this investigation Hagino et al. described the use of x-ray diffractometry for the determination of the mixing ratio of ingredients compounded in rubber. This method was also suggested for the quantitative analysis of zinc oxide, but no studies were reported. During a study in this laboratory to determine the role of zinc oxide in the vulcanization of rubber, a new analytical method, based on x-ray diffractometry, was developed. The method was rapid, nondestructive, and simple. The data were reliable and accurate.

Effects of cholesterol on the structural transitions induced by diacylglycerol in phosphatidylcholine and phosphatidylethanolamine bilayer systems

1990 ◽  
Vol 68 (1) ◽  
pp. 65-69 ◽  
Author(s):  
Jens R. Coorssen ◽  
R. P. Rand
Keyword(s):  
Plasma Membranes ◽  
Membrane Lipid ◽  
Enzyme Activation ◽  
Structural Effects ◽  
X Ray Diffraction ◽  
Major Fraction ◽  
X Ray ◽  
Lipid Mixtures

The transient membrane lipid diacylglycerol (DG) is known to modify and destabilize phospholipid bilayers and can lead to the formation of nonbilayer structures. Since cholesterol forms a major fraction of many plasma membranes, we have investigated how it modifies the structural effects of DG on bilayers of egg phosphatidylcholine (PC) and egg phosphatidylethanolamine (PE). We view these systems as modelling the behaviour of local, DG-containing sites in membranes. Using X-ray diffraction, we have characterized the lamellar (Lα) and inverse hexagonal (HII) structures that these ternary lipid mixtures form in excess aqueous solution. As the DG level increases, the lipid progresses from a single Lα structure to a mixture of Lα and HII, and then to a pure HII structure. This allows determination of the DG levels at which the HII transition begins, which we interpret as those levels that destabilize bilayers. In both PC and PE bilayers, the presence of 30 mol% cholesterol reduces the amounts of DG required to destabilize the bilayer structure. The destabilization can be translated into the number of neighbouring lipid molecules that a DG molecule perturbs, and of bilayer areas that it affects. The data show that the presence of cholesterol greatly enhances the perturbing effects of DG. We examine the possible role of DG in enzyme activation and membrane fusion.Key words: diacylglycerol, cholesterol, bilayers, phosphatidylcholine, phosphatidylethanolamine.

scholarly journals Contents of heavy metals in the soil cover in the conditions of technogenesis

2016 ◽  
Vol 5 (1) ◽  
pp. 34-37
Author(s):  
Ivan Victorovich Kazantsev ◽  
Tatyana Borisovna Matveeva
Keyword(s):  
Heavy Metals ◽  
Maximum Permissible Concentration ◽  
Botanical Garden ◽  
X Ray ◽  
Nickel Chromium ◽  
Forest Belts ◽  
Green Zone ◽  
Suburban Forests

The paper examines pollution of soils with heavy metals under technogenic impact. The ways and means of pollutants receipt in soils and their accumulation in soils located in the drainage of railway are described. The role of roadside forest belts on the distribution of pollutants is examined. Determination of heavy metals content in soils was carried out by the x-ray fluorescence method. The results of heavy metal soil pollution in comparison with Clarke value, maximum permissible concentration and regional background levels are represented. The study of heavy metals content was carried out in the soils of right-of-way on the Samara-Syzran section of the Kuibyshev railway, as well as in suburban forests and urban parks of Samara (Botanical garden, Country Park). These areas are exposed to significant anthropogenic impact. Studies have shown that in these areas an increased content of some heavy metals in soils is observed. The main elements present in anthropogenic flows of pollution are copper, nickel, chromium, zinc and lead. This result does not contradict the standard environmental situation. These materials can serve as a basis for further monitoring of suburban forests of Samara green zone and transport facilities

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