共查询到20条相似文献,搜索用时 0 毫秒
1.
粉末X射线衍射图谱计算植物淀粉结晶度方法的探讨 总被引:6,自引:0,他引:6
植物淀粉有A-型、B-型和C-型3种晶体。以水稻(Oryza sativa)、马铃薯(Solanum tuberosum)、豌豆(Pisum sativum) 和莲藕(Nelumbo nucifera)淀粉为材料, 利用粉末X-射线衍射仪(XRD)调查了不同晶体类型淀粉的波谱特征, 探讨XRD波谱相对结晶度的计算方法。软件峰拟合法、软件曲线法、直线作图法和曲线作图法均可用于计算淀粉XRD波谱的相对结晶度, 以曲线作图法计算结果较为可靠。利用曲线作图法得出的结果表明, 稻米淀粉的结晶度与直链淀粉含量呈显著线性负相关, 酸解莲藕淀粉的结晶度与淀粉酸水解度呈显著线性正相关。酸水解使莲藕淀粉的C-型晶体转变为A-型晶体。上述研究结果为利用XRD分析植物淀粉晶体类型和计算相对结晶度提供了重要参考。 相似文献
2.
3.
The submicroscopic structure of the starch grains of Zea maysand Triticum sativum was studied electron-optically from replicasmade of internal, fracture surfaces. In corn starch, long cylindricalmicrofibrils were found, arranged in a radial direction andimbedded in an amorphous matrix. Their diameter was uniformlyabout 200 Å. Microfibrils were also indicated in wheatstarch because of the prominence of their ends in surface view.Many microfibrils in corn starch appeared to be helically coiled.The more ordered starch substance was presumed to be localizedprincipally in the microfibrils. 相似文献
4.
Keiichi Fukuyama Tomitake Tsukihara Yukiteru Katsube Takashi Hamasaki Yuichi Hatsuda 《Bioscience, biotechnology, and biochemistry》2013,77(5):1053-1054
Streptomyces sp. No. 280 produced several kinds of amylase inhibitors (amylase inhibitor A, B, B' and C). Two amylase inhibitors (designated as AI-A1 and AI-A2) were obtained from an amylase inhibitor A fraction by paper chromatography. AI-A1 inhibited muscle phosphorylase a much more than AI-A2 and was hydrolyzed by sweet potato β-amylase whereas AI-A2 was not. Both amylase inhibitors had a carbohydrate and were hydrolyzed by some kinds of amylases or acids. They lost their inhibitory activity against phosphorylase a after treatment with acids or hog pancreatic α-amylase, but they showed increased inhibitory activity toward porcine small intestinal sucrase.Both AI-A1 and AI-A2 were composed of glucose and a basic moiety which gave a positive ninhydrin reaction. The molecular weights of AI-A1 and AI-A2 were estimated to be approximately 1300 ? 1500 by gel filtration on a Sephadex G-15 column. The nitrogen content of the amylase inhibitors was found to be about 1.3% by elementary analysis 相似文献
5.
Sylvie Chevallier Anne-Laure Réguerre Alain Le Bail Guy Della Valle 《Food biophysics》2014,9(3):219-228
The cellular structure of two products, an extruded breakfast cereal and a short dough biscuit, was characterized by two different X-ray micro computed tomographic systems. Acquisitions were made by a compact desktop system Skyscan 1174 (Bruker μCT, Belgium) and at the European Synchrotron Radiation Facility (ESRF, beamline ID19, France) at different resolutions (voxel size of 6.5 μm, 7.5 μm, 16.2 μm and 25.8 μm). 3D images were processed for the density, the connectivity index and the granulometry of cells and cell walls. These experiments underlined the importance of the resolution for determination of quantitative measurements such as densities and thicknesses. The median width calculated for the cell walls distribution in the biscuit dropped from 141 to 50 μm when the voxel size changed from 25.8 to 7.5 μm. Images well showed that even though the food products had close values of porosity 0.6 and 0.7 for biscuit and extruded breakfast cereal respectively, their cellular structures were very different. The biscuit had small cells (median value of the distribution varied from 125 to 152 μm, according to resolution) and larger cell walls (50–141 μm) than the extrudate (32–109 μm) which, on the contrary, exhibited very large cells (307–400 μm). Beyond methodological issues, these differences could be clearly attributed to the differences of compositions and processes. 相似文献
6.
Balasundaresan Dhakshnamoorthy Suchismita Raychaudhury Lydia Blachowicz 《Journal of molecular biology》2010,396(2):293-2115
The OmpF porin from the Escherichia coli outer membrane folds into a trimer of β-barrels, each forming a wide aqueous pore allowing the passage of ions and small solutes. A long loop (L3) carrying multiple acidic residues folds into the β-barrel pore to form a narrow “constriction zone”. A strong and highly conserved charge asymmetry is observed at the constriction zone, with multiple basic residues attached to the wall of the β-barrel (Lys16, Arg42, Arg82 and Arg132) on one side, and multiple acidic residues of L3 (Asp107, Asp113, Glu117, Asp121, Asp126, Asp127) on the other side. Several computational studies have suggested that a strong transverse electric field could exist at the constriction zone as a result of such charge asymmetry, giving rise to separate permeation pathways for cations and anions. To examine this question, OmpF was expressed, purified and crystallized in the P63 space group and two different data sets were obtained at 2.6 Å and 3.0 Å resolution with K+ and Rb+, respectively. The Rb+-soaked crystals were collected at the rubidium anomalous wavelength of 0.8149 Å and cation positions were determined. A PEG molecule was observed in the pore region for both the K+ and Rb+-soaked crystals, where it interacts with loop L3. The results reveal the separate pathways of anions and cations across the constriction zone of the OmpF pore. 相似文献
7.
8.
9.
Takaaki Sugiyama Daisuke Takao Yasunobu Sugimoto Shinji Kamimura 《Biophysical journal》2009,97(12):3132-3138
X-ray fiber diffraction is one of the most useful methods for examining the structural details of live biological filaments under physiological conditions. To investigate biologically active or labile materials, it is crucial to finish fiber alignment within seconds before diffraction analysis. However, the conventional methods, e.g., magnetic field alignment and low-speed centrifugations, are time-consuming and not very useful for such purposes. Here, we introduce a new alignment method using a rheometer with two parallel disks, which was applied to observe fiber diffractions of axonemes, tobacco mosaic tobamovirus, and microtubules. We found that fibers were aligned within 5 s by giving high shear flow (1000-5000 s−1) to the medium and that methylcellulose contained in the medium (∼1%) was essential to the accomplishment of uniform orientation with a small angular deviation (<5°). The new alignment method enabled us to execute structure analyses of axonemes by small-angle x-ray diffraction. Since this method was also useful for the quick alignment of purified microtubules, as well as tobacco mosaic tobamovirus, we expect that we can apply it to the structural analysis of many other biological filaments. 相似文献
10.
ORD and CD of d(+) pantothenic acid, d(+) pantothenyl alcohol and d(?) pantolactone were studied. The acid and the alcohol gave positive Cotton effects with a peak at 227 and 225 mμ, respectively, and the lactone gave a negative Cotton effect with trough at 233 mμ. They gave CD maxima at 214, 213 and 219 mµ corresponding to the inflection points of their ORD curves.The concentrations were found to be linear to the rotation angles and the possibility of the application to quantitative analysis of the ORD was cited. The ORD showed the quantitative formation of the lactone by acid treatment of the vitamins without any racemization and hence the determination via lactone was suggested. 相似文献
11.
Chlorites in the bio interaction zone (or rhizosphere soils) are transformed by bacteria, fungi and mosses into expanding 2:1 minerals with different cation fixation capacities. Some of the new clays are smectitic, expanding with glycol treatment in the Ca-saturated state, while others have a high intensity 001 peak unchanged by glycol treatment. Most of all, potassium saturation results in different hydration states in mixed layered phases or as individual illitic units or minerals indicating dissimilarity in charge site and intensity on the 2:1 layers of the original chlorites. However, the overall pattern is that of the transformation of high temperature chlorite to expanding clay minerals with high exchange capacities. Biotic processes appear to modify chlorites in a rather homogeneous manner compared to the formation of interstratified minerals common in the water-rock interaction pathway. These high charge expanding clays left after the biologically mediated reactions with chlorites are strong potential sites for cation (e.g., magnesium and potassium) capture and storage to supply the nutritional requirements of plants and organisms. 相似文献
12.
The purpose of this study was to establish a calibration model to predict the hydrate content in powder materials consisting
of anhydrate (theophylline anhydrate (THA)) and theophylline monohydrate (THM) by using various kinds of X-ray powder diffraction
(XRPD) analytical methods. XRPD profiles were measured five times each for 11 standard samples containing of THA and THM.
THM content in the standard samples was evaluated based on XRPD profiles by the diffraction peak height and area methods,
and the Wakelin’s and principal component regression (PCR) methods, respectively. Since THA and THM were cube- and rod-shaped
particles, the standard samples consisted of THA and THM showed crystal orientation due to THM crystal shape. THA showed reproducible
XRPD profiles, but THM showed fluctuating intensities in some specific peaks in the profiles. The linear calibration models
were evaluated based on calibration XRPD datasets of the standard materials by various methods. In the result based on validation
XRPD datasets, the order of the mean bias and the mean accuracy were peak height > peak area > Wakelin’s > PCR, indicating
that PCR was the best method to correct sample crystal orientation. The effectiveness of the PCR method in construction of
calibration models was discussed by a scientific approach based on regression vectors. 相似文献
13.
H. E. Huxley 《The Journal of general physiology》1967,50(6):71-83
The sliding filament model for muscular contraction supposes that an appropriately directed force is developed between the actin and myosin filaments by some process in which the cross-bridges are involved. The cross-bridges between the filaments are believed to represent the parts of the myosin molecules which possess the active sites for ATPase activity and actin-binding ability, and project out sidewise from the backbone of the thick filaments. The arrangement of the cross-bridges is now being studied by improved low-angle X-ray diffraction techniques, which show that in a resting muscle, they are arranged approximately but not exactly in a helical pattern, and that there are other structural features of the thick filaments which give rise to additional long periodicities shown up by the X-ray diagram. The actin filaments also contain helically arranged subunits, and both the subunit repeat and the helical repeat are different from those in the myosin filaments. Diffraction diagrams can be obtained from muscles in rigor (when permanent attachment of the cross-bridges to the actin subunits takes place) and now, taking advantage of the great increase in the speed of recording, from actively contracting muscles. These show that changes in the arrangement of the cross-bridges are produced under both these conditions and are no doubt associated in contraction with the development of force. Thus configurational changes of the myosin component in muscle have been demonstrated: these take place without any significant over-all change in the length of the filaments. 相似文献
14.
木薯淀粉在一定温度下用乙醇和碱的混合液处理,用HCl中和,醇洗,最后在50℃左右的烘箱中干燥6h,X射线衍射结果表明经碱醇处理的木薯淀粉其微晶、亚微晶、非晶的组成发生了变化。不同的处理条件,结晶组成的变化不同。较低浓度的醇,较高浓度的碱或较高反应温度得到非晶化程度高一些的淀粉。在偏光显微镜下观察到较少的偏光十字,表明淀粉的结晶结构发生了变化。 相似文献
15.
Electron Microscope and X-ray Diffraction Studies of a Saturated Synthetic Phospholipide 总被引:4,自引:3,他引:1
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
J. B. Finean 《The Journal of cell biology》1959,6(1):123-124
16.
Margarine and fat spread contain typical water-in-oil emulsions, including semi-solid fats, as continuous oil phases. The
application of palm oil, one of the most promising trans-fat alternatives, for semi-solid fats is increasing. However, granular crystals often occur in palm-oil-based solid fats
and cause deterioration. In this study, we carried out differential scanning calorimetry (DSC), optical microscopy, and X-ray
diffraction (XRD) experiments on granular crystals in margarine. A conventional laboratory-scale technique was applied to
examine thermal properties of high-melting fat fractions in granular crystals. In addition, microstructures of the granular
crystal were precisely observed with a synchrotron radiation small-angle XRD (SR-μ-SAXD) technique by using a microbeam having
a cross section of 5 × 5 μm2. The following results were obtained. (1) DSC indicated that granular crystals are composed of high-melting fractions having
a melting temperature of 23 °C. (2) Conventional XRD of granular crystals indicated that β-fat crystals of a triple chain
length structure (β-3) melted below the melting of β′-fat of a double chain length structure (β′-2). (3) SR-μ-SAXD indicated
that the fat crystals in normal margarine were β′-2. However, the fat crystals of the double and triple chain length structures
were simultaneously observed at the center region of a granular crystal, whereas only the fat crystals of β-3 were observed
at the outer region of a granular crystal. We analyzed the microstructures and formation processes of granular crystals in
relation to the fractional crystallization of the β form of 1,3-dipalmitoyl-2-oleoyl-sn-glycerol promoted by crystallization and transformation of tripalmitin and tristearin fractions. 相似文献
17.
X-ray Diffraction Studies of Cell Walls and Peptidoglycans from Gram-positive Bacteria 总被引:4,自引:0,他引:4
THE cell walls of Gram-positive bacteria consist principally of a water-insoluble polymer and peptidoglycan (synonyms, murein, mucopeptide, glycosaminopeptide), which in some cases accounts for as much as 90% of the cell wall. After other components (teichoic acid, teichuronic acid, polysaccharide or protein) have been gently removed from the cell walls, peptidoglycan remains as a cell-shaped structure at least 100 Å thick. We report here results of X-ray diffraction observations on whole cell walls and peptidoglycans of Staphylococcus aureus, Bacillus licheniformis and Micrococcus lysodeikticus. Chemical data shows that all the muramic acid residues in the glycan chains of the peptidoglycan of S. aureus are substituted with the peptide L Ala-D GluNH2-L Lys-D Ala and that there is extensive cross linking by pentaglycine bridges between peptides on adjacent glycan chains1,3. Such a peptidoglycan might be expected to have an ordered crystalline structure. On the contrary, peptidoglycans of the bacilli, in which the cross linking between peptides is direct and considerably less4,5 might be expected to have a less ordered structure. The mode of packing of the glycan and peptide moieties has been considered by Kelemen and Rogers6. When the glycan chains are stacked in pairs, as in the analogous polysaccharide chitin7, the muramic acid residues are orientated in such a way as to allow a three-dimensional structure to be built. If the bulk of the peptides are then arranged in a pseudo β configuration, calculations show that the expected dimensions of the cell wall calculated from the model are of the right order and also such a model allows for the existence of extensive stabilizing hydrogen bonds between adjacent peptide chains. 相似文献
18.
H. Courtney Gage 《BMJ (Clinical research ed.)》1941,2(4222):825-826
19.
IN our continuing studies on the crystallography of tRNA1 we have obtained a new crystal form of phenylalanine tRNA from baker's yeast. The crystals show particularly good stability to X-ray irradiation, lasting generally for about 100 h in the X-ray beam. Most importantly they produce reflexions which extend out to a resolution of about 3.0 Å. The crystals belong to the monoclinic system, space group P2i with two molecules of tRNA per unit cell (Table 1). Thus, there is only one molecule per asymmetric unit of structure. The unit cell dimensions (a=56.0, b=33.4, c=63.0 and β=90.9°) are the smallest yet reported for tRNA and place stringent constraints on the possible dimensions of the tRNA molecule. 相似文献
20.
Marianne Rooman Emilie Cauët Jacques Liévin René Wintjens 《Journal of biomolecular structure & dynamics》2013,31(6):949-954
Abstract Electron holes are known to migrate along the DNA or RNA duplexes and to localize preferentially on successive guanines. The stationary point conformations of Gua pairs that can trap or let pass these holes have been characterized by quantum chemistry calculations. Here we show their recurrent occurrence in DNA and RNA X-ray structures, often in quadruplex conformations or in interaction with proteins, ligands or metal ions. These findings give support to the biological, possibly regulatory, roles of charge migration in cell functioning. 相似文献