PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “X-Ray Diffraction”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 451 records · Page 25Linked to original sources
PubMed1978

[Radiocrystallographic study of 46 salivary calculi. Physiopathogenic hypotheses (author's transl)].

The radiocrystallographic study of 46 salivary calculi using the Debye and Scherrer powder methods showed that such stones, whether submaxillary, parotid or "accessory" consist essentially of hydroxyapatite with the frequent presence of tricalcium and octocalcium phosphates, Whitlockite and rarely Brushite and Calcite. In order for a stone to form, the following conditions would seem to be necessary; transient supersaturation of the saliva in Ca++ and PO4--, a pH greater than normal, intracellular precepitation of amorphous tricalcium phosphate which is transformed into crystalline hydroxyapatite and, then, the fixation of crystals on a "matrix" such as desquamated cells, fibrils and collagens.

Adolescent↗
PubMed1978

[Hydroxylapatite ceramics--a bone-like biomaterial. Preliminary report].

Inorganical materials are being increasingly tried out in surgery and periodontal surgery for reconstructing bone defects. This paper discusses the biocompatibility and biofunctionality of different implant materials and presents a new hydroxyapatite ceramic material, of which a good bioactive behaviour is expected.

Biocompatible Materials↗
PubMed1978

Crystallographic studies on D-amino acid oxidase.

D-amino acid oxidase, a flavoprotein from hog kidneys, has been crystalized in two different forms. Orthorhombic prisms have been obtained from the enzyme.benzoate complex at pH 8.3; the space group is C2221 and the cell dimensions are a = 325A, b = 138.8 A, c = 200 A. At lower pH values, the enzyme crystallizes in trigonal prisms with a = b = 116.0 A, c = 399 A, space group P3112 or its enantiomorph. The two crystal forms have been obtained at 28 degrees C while at 4 degrees C only weak evidence of crystallization has been detected. In both crystalline modifications, the protein is highly associated.

D-Amino-Acid Oxidase↗
PubMedDate not supplied

[DNA complexes with lysozyme].

Sedimentation method has been used to study hen egg-white lysozyme binding to glucosylated (from T2 phage) and non-glucosylated (from calf thymus) DNA under conditions similar to physiological ones (pH 7,3--7,4, ionic strength 0.07--0.24). The results indicate that lysozyme binds cooperatively to both DNA's. Binding parameters have been obtained by applying the theory of one-dimensional adsorption of small molecules on a linear homopolymer. X-ray patterns of complexes with different protein content have been obtained.

Animals↗
PubMed1976

X-ray and functional studies of hemoglobins Nancy and Cochin-Port-Royal.

The mutations in hemoglobin Nancy beta145(HC2) Tyr leads to Asp and hemoglobin Cochin-Portal-Royal beta146(HC3) His leads to Arg involve residues which are thought to be essential for the full expression of allosteric action in hemoglobin. Relative to the structure of deoxyhemoglobin A, our x-ray study of deoxyhemoglobin Nancy shows severe disordering of the beta chain COOH-terminal tetrapeptide and a possible movement of the beta heme iron atom toward the plane of the porphyrin ring. These structural perturbations result in a high oxygen affinity, reduced Bohr effect, and lack of cooperatively in hemoglobin Nancy. In the presence of inositol hexaphosphate (IHP), the Hill constant for hemoglobin Nancy increases from 1.1 to 2.0. But relative to its action on hemoglobin A, IHP is much less effective in reducing the oxygen affinity and in increasing the Bohr effect of hemoglobin Nancy. This indicates that IHP does not influence the R in equilibrium T equilibrium as much in hemoglobin Nancy as in hemoglobin A, and this probably is due to the disordering of His 143beta which is known to be part of the IHP binding site. IHP is also known to produce large changes in the absorption spectrum of methemoglobin A, but we find that it has no effect on the spectrum of methemoglobin Nancy. In contrast to the large structural changes in deoxyhemoglobin Nancy, the structure of deoxyhemoglobin Cochin-Port-Royal differs from deoxyhemoglobin A only in the position of the side chain of residue 146beta. The intrasubunit salt bridge between His 146beta and Asp 94beta in deoxyhemoglobin A is lost in deoxyhemoglobin Cochin-Portal-Royal with the guanidinium ion of Arg 146beta floating freely in solution. This small difference in structure results in a reduced Bohr effect, but does not cause a change in the Hill coefficient, the response to 2,3-diphosphoglycerate, or the oxygen affinity at physiological pH.

Allosteric Site↗
PubMedDate not supplied

[Myelin].

The lipid and protein composition and the metabolic turnover of myelin in the C.N.S., are briefly reported. For a better understanding, it seemed useful to introduce some historical data on the discovery of myelin and to give a morphological description at structural and ultrastructural level.

Animals↗
PubMed1977

Structure and interactions of lipids in human plasma low density lipoproteins.

Temperature-dependent techniques (differential scanning calorimetry, polarizing microscopy, and x-ray scattering and diffraction techniques) were used to compare the properties of human plasma low density lipoproteins (LDL) with its extracted lipid classes. Three types of thermal transitions were characterized: (a) a reversible transition in intact LDL near body temperature associated with a liquid crystalline order-disorder phase change of cholesterol esters within the particles; (b) an irreversible high temperature transition (approximately 70-90 degrees) associated with LDL denaturation and release of cholesterol esters from the disrupted particles; and (c) low temperature transitions related to liquid crystalline and crystalline phase changes in these released esters. The temperature of the reversible transition in intact LDL varies among individual donors. Correlation analysis shows that the temperature of this transition negatively correlates with the amount of triglyceride relative to cholesterol ester in LDL. Studies on mixtures of cholesterol esters and triglycerides isolated from LDL show a similar effect, increasing amounts of triglycerides decreasing the temperature of the liquid leads to smectic liquid crystalline transition of the isolated esters. Thus, the amount of triglyceride in LDL influences the fluidity of the cholesterol esters in LDL. The enthalpy of the reversible transition in intact LDL is 0.69 cal/g of LDL cholesterol ester. This compares with 0.89 cal/g for the liquid leads to liquid crystalline transition of the cholesterol esters released from denatured LDL and 1.01 cal/g for the same transition in the extracted esters. Unlike the cholesterol esters released from denatured LDL, or isolated LDL esters, cholesterol ester in the intact LDL particle does not crystallize. These findings suggest that the behavior of cholesterol esters in intact LDL is constrained relative to their behavior when freed from the restrictions of the particle. These results together with experiments on partitioning of the individual lipid classes of LDL allow us to define the distribution and interaction of lipids in the intact LDL particle.

Calorimetry↗
PubMed1977

X-ray analysis of enzymically purified elastin from bovine ligamentum nuchae.

Insoluble elastin has been isolated from bovine ligamentum nuchae by treatment with quanidine and dithiothreitol followed by digestion with collagenase, purified by affinity chromatography. The preparation was subjected to both wide- and low-angle X-ray analysis. The wide-angle diffraction patterns of relaxed and stretched specimens showed only two broad diffraction rings, corresponding to spacings of 4.5 and 9.3 A. No significant reflections were visible in the low-angle diffraction pattern of unstretched specimens, but on stretching an equatorial reflection was produced, corresponding to spacings of between 45 and 50 A.

Animals↗
PubMed1977

The identification of particulate matter in biological tissues and fluids.

Sections, 1-2 micron thick, of Araldite embedded tissue were prepared to provide a link between optical and electron microscopy for the identification of crystals. This technique permits examination of individual particles by means of polarising light microscopy, electron microscopy, X-ray energy spectroscopy and electron diffraction. It provides a reliable method for routine and research studies. It has led to the positive identification of individual crystals of calcium pyrophosphate dihydrate and hydroxyapatite in synovial fluids. The method can be applied to the identification of other particulate matter in a variety of biological specimens.

Aged↗