Low-angle X-ray Diffraction Studies Research Articles

A low-angle X-ray diffraction study of the swelling behavior of peripheral nerve myelin

The swelling behavior of peripheral nerve myelin has been studied by recording low-angle X-ray diffraction patterns of nerve after various chemical treatments. Peripheral myelin swells in distilled water, hypotonic Ringer's solution and sucrose solutions. The resulting low-angle pattern is called a swollen pattern (by comparison, the normal pattern is obtained from live nerve). The swelling of myelin is reversed by a reimmersion of the nerve in salt solutions and the resulting low-angle pattern is called a subnormal pattern. A relationship between these three kinds of patterns is given in terms of the width of the membrane pair. The forces between the adjacent membrane pairs in swollen myelin are likely to be long-range attractive Van der Waals' and long-range electrical repulsive forces. However, an equilibrium between the attrative and repulsive forces has not been observed.

THE RELATIONSHIP BETWEEN MYOFILAMENT PACKING DENSITY AND SARCOMERE LENGTH IN FROG STRIATED MUSCLE

In cross-sections of single fibers from the frog semitendinosus muscle the number of thick myofilaments per unit area (packing density) is a direct function of the sarcomere length. Our data, derived from electron microscopic studies, fit well with other data derived from in vivo, low-angle X-ray diffraction studies of whole semitendinosus muscles. The data are consistent with the assumption that the sarcomere of a fibril maintains a constant volume during changes in sarcomere length. The myofilament lattice, therefore, expands as the sarcomere shortens. Since the distance between adjacent myofilaments is an inverse square root function of sarcomere length, the interaction of the thick and the thin myofilaments during sarcomere shortening may occur over distances which increase 70 A or more. The "expanding-sarcomere, sliding-filament" model of sarcomere shortening is discussed in terms of the current concepts of muscle architecture and contraction.

Low-angle X-ray diffraction studies of living striated muscle during contraction

The spacings and intensities of the small-angle equatorial X-ray reflexions from living toad sartorius muscle were studied in the resting and contracted state. On contraction, there is a small and nearly constant decrease of 6 to 12 Å in the lattice spacing over the whole range of muscle lengths studied and the 1,1 reflexion becomes slightly more intense relative to the 1,0 reflexion. In both resting and contracting muscle, the centre-to-centre distance between actin and myosin filaments depends on sarcomere length, being about 80 Å larger in the short muscles (sarcomere length 2.1 μ) than in the long ones (sarcomere length 3.6 μ). In another set of experiments with the toad sartorius muscle, it was found that on contraction no change occurred in the spacings of the meridional X-ray reflexions from either the actin or the myosin filaments. We have also observed a decrease in intensity of the myosin layer lines (given by the projections on the myosin filaments) as first reported by Huxley, Brown & Holmes (1965). By indicating that there is no change in length in the actin or myosin filaments during contraction, these results provide general support for the sliding filament hypothesis.

Low-angle x-ray diffraction and electron-microscope studies of isolated cell membranes.

ABSTRACT A sequence of low-angle X-ray diffraction patterns obtained during the controlled drying of a preparation of rat erythrocyte ghosts has been interpreted with the aid of corresponding electron micrographs and of a parallel study of myelin isolated from guinea-pig brain. A diffraction pattern that persists down to a level of 10–20 % hydration of the sample is believed to arise from the close packing of native erythrocyte membranes. Each membrane is about 100 Å thick and it is suggested that it consists of a predominantly continuous bimolecular layer of lipid, with non-lipid components associated with both surfaces. Further changes in diffraction pattern which accompany continued drying could be interpreted either as a change from a lamellar to a hexagonal structure or as the formation of a multiphase system. Evidence is put forward to support the latter interpretation.

Electron microscope and low-angle X-ray diffraction studies on outer segment membranes from the retina of the frog

Ordered arrays of particles about 40 Å in diameter within the outer segment membranes of retinal receptor have been observed by electron microscopy, and low-angle X-ray diffraction studies are in agreement with this finding. Surface-on views of outer segment membranes negatively-stained with phospho-tuhgstate or fixed with permanganate show square arrays of particles with a non-polar core 40 Å in diameter. Light diffraction patterns of a mask of holes simulating electron micrographs showed first and second orders of a uniformly square array with a unit cell side of about 70 Å.

A LOW-ANGLE X-RAY DIFFRACTION STUDY OF BACTERIAL FLAGELLA.

Abstract In order to differentiate between the various proposed models for the structure bacterial flagella, low-angle X-ray diffraction studies have been carried out on wet specimens of Proteus vulgaris . The low-angle equatorial diffraction pattern has been obtained and compared with the theoretically calculated patterns for a rod model and the double and triple helical structures according to Labaw and Mosley . The comparison shows that a model comprised of helical filaments is the most likely structure. Fourier-Bessel transformation of the experimental scattering data has been performed and the radial density-distribution curve gives low values in the middle of the structure, suggesting the flagellum has a hollow center, thus favouring the triple helical form.

A Technique for Low‐Angle X‐Ray Diffraction Studies on Expanded Three‐Layer Clays

Soil Science Society of America JournalVolume 27, Issue 2 p. 241-242 Note A Technique for Low-Angle X-Ray Diffraction Studies on Expanded Three-Layer Clays† D. H. Fink, D. H. Fink Agronomy Department, Virginia Polytechnic Institute, BlacksburgSearch for more papers by this authorG. W. Thomas, G. W. Thomas Agronomy Department, Virginia Polytechnic Institute, BlacksburgSearch for more papers by this author D. H. Fink, D. H. Fink Agronomy Department, Virginia Polytechnic Institute, BlacksburgSearch for more papers by this authorG. W. Thomas, G. W. Thomas Agronomy Department, Virginia Polytechnic Institute, BlacksburgSearch for more papers by this author First published: 01 March 1963 https://doi.org/10.2136/sssaj1963.03615995002700020046x † Contribution from the Agronomy Department, Virginia Polytechnic Institute, Blacksburg. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume27, Issue2March-April 1963Pages 241-242 RelatedInformation

Electron microscope and low-angle x-ray diffraction studies of the nerve myelin sheath.

1. A close correlation has been obtained between high resolution electron microscopy and low-angle x-ray diffraction studies of the myelin sheath of frog and rat peripheral and central nerves. Extensive studies were performed by application of both techniques to the same specimens, prepared for examination by OsO(4) or KMnO(4) fixation, and embedding either in methacrylate or in gelatin employing a new procedure. Controlled physical and chemical modifications of the myelin sheath prior to fixation were also investigated. 2. A correspondence was established between the layer spacings observed in electron micrographs and the fundamental radial repeating unit indicated by the low-angle x-ray diffraction patterns. The variations in relative intensities of the low-angle x-ray reflections could be related to the radial density distributions seen in the electron micrographs. 3. An analysis of the preparation procedures revealed that OsO(4) fixation introduces a greater shrinkage of the layer spacings and more pronounced changes in the density distribution within the layers than KMnO(4) fixation. The effects of methacrylate and gelatin embedding are described, and their relative merits considered in relation to the preservation of myelin structure by OsO(4) fixation. 4. The experimental modifications introduced by freezing and thawing of fresh whole nerve are described, particularly the enhancement of the intermediate lines and the dissociation of the layer components in the myelin sheath. A characteristic collapsing of the radial period of the sheath is observed after subjecting fresh nerve trunks to prolonged and intense ultracentrifugation. 5. Controlled extraction of fresh nerve with acetone at 0 degrees C., which preferentially removes cholesterol, produces characteristic, differentiated modifications of the myelin sheath structure. Electron microscopy reveals several types of modifications within a single preparation, including both expanded and collapsed layer systems, and internal rearrangements of the layer components. Alcohol extraction leads to a more extensive structural breakdown, but in certain areas collapsed layer systems can still be observed. The components of the lipide extracts could be identified by means of x-ray diffraction. These modifications emphasize the importance of cholesterol in the myelin structure, and disclose a resistance of the dense osmiophilic lines to lipide solvents. 6. The significance of these structures is discussed in relation to present concepts of the molecular organization of myelin. The available evidence is consistent with the suggestion that the primary site of osmium deposition is at the lipoprotein interfaces and that the light bands probably represent regions occupied by lipide chains. The electron microscope and x-ray diffraction data also indicate the possibility of a regular organization within the plane of the layers, probably involving units of 60 to 80 A. The myelin sheath is regarded as a favourable cell membrane model for detailed analysis by combined application of x-ray diffraction and electron microscopy.

Low-angle X-ray diffraction study of the polymorphic forms of synthetic α:β and α:α′-kephalins and α:β-lecithins

Low-angle X-ray diffraction study of the polymorphic forms of synthetic α:β and α:α′-kephalins and α:β-lecithins

Effect of Orientation on the Mechanical Properties of Polystyrene

Abstract Extruded polystyrene rod was first annealed, and then stretched hot to elongations as high as 12,000 per cent. Tests were made in tension, flexure, and torsion at temperatures ranging from 0 to 80 C. Tests included creep and relaxation as well as tests at strain and load rates ranging as high as 1.0 in/in/min and 10,000 lb per min to determine the effect of orientation upon these mechanical properties. Tensile and flexural strengths increased two to threefold, depending upon rate and temperature; torsional strength decreased; and modulus of elasticity increased moderately. Fracture changed from a sharp break to a fibrous separation. Birefringence measurements revealed marked orientation of the material, but low-angle x-ray diffraction studies revealed no “crystalline” structure.

Point-Focus X-Ray Monochromators for Low Angle Diffraction

Guinier has applied the principle of the reflection type curved crystal focusing x-ray monochromator to improve both intensity and angular resolution in low angle x-ray diffraction studies. In Guinier's method, a thin sample is placed in the convergent monochromatic x-ray beam and the low angle diffraction pattern is formed as a diffuse distribution symmetrically disposed on either side of the central primary line focused by the crystal.