scholarly journals Cross-linker system between neurofilaments, microtubules and membranous organelles in frog axons revealed by the quick-freeze, deep-etching method

1982 ◽  
Vol 94 (1) ◽  
pp. 129-142 ◽  
Author(s):  
N Hirokawa
Keyword(s):  
Chemical Extraction ◽  
Distilled Water ◽  
Deep Etching ◽  
Cross Links ◽  
Cross Linker ◽  
The Cross ◽  
Cross Bridges ◽  
20 Nm ◽  
Soluble Material ◽  
Soluble Components

The elaborate cross-connections among membranous organelles (MO), microtubules (MT), and neurofilaments (NF) were demonstrated in unifixed axons by the quick-freeze, deep-etch, and rotary-shadowing method. They were categorized into three groups: NF-associated cross-linker, MT-associated cross-bridges, and long cross-links in the subaxolemmal space. Other methods were also employed to make sure that the observed cross-connections in the unfixed axons were not a result of artifactual condensation or precipitation of soluble components or salt during deep-etching. Axolemma were permeablized either chemically (0.1% saponin) or physically (gentle homogenization), to allow egress of their soluble components from the axon; or else the axons were washed with distilled water after fixation. After physical rupture of the axolemma or saponin treatment, most of the MO remained intact. MT were stabilized by adding taxol in the incubation medium. Axons prepared by these methods contained many longitudinally oriented NF connected to each other by numerous fine cross-linkers (4-6 nm in diameter, 20-50 nm in length). Two specialized regions were apparent within the axons: one composed of fascicles of MT linked with each other by fine cross-bridges; the other was in the subaxolemmal space and consisted of actinlike filaments and a network of long cross-links (50-150 nm) which connected axolemma and actinlike filaments with NF and MT. F-actin was localized to the subaxolemmal space by the nitrobenzooxadiazol phallacidin method. MO were located mainly in these two specialized regions and were intimately associated with MT via fine short (10-20 nm in length) cross-bridges. Cross-links from NF to MO and MT were also common. All these cross-connections were observed after chemical extraction or physical rupture of the axon; however, these procedures removed granular materials which were attached to the filaments in the fresh unextracted axons. The cross-connections were also found in the axons washed with distilled water after fixation. I conclude that the cross- connections are real structures while the granular material is composed of soluble material, probably protein in nature.

Photodegradable cross-linked polymer derived from a vinylic rotaxane cross-linker possessing aromatic disulfide axle

2013 ◽  
Vol 85 (4) ◽  
pp. 835-842 ◽  
Author(s):  
Yasuhito Koyama ◽  
Takahiro Yoshii ◽  
Yasuhiro Kohsaka ◽  
Toshikazu Takata
Keyword(s):  
Crown Ether ◽  
Methyl Methacrylate ◽  
Radical Polymerization ◽  
Vinyl Monomer ◽  
Hydroxymethyl Group ◽  
Cross Links ◽  
Cross Linker ◽  
The Cross ◽  
Vinyl Group ◽  
Site Selective

A new concept for photodegradable cross-linked polymers utilizing characteristics of rotaxane cross-links and aromatic disulfides is proposed. The cross-linked polymer is obtained by the radical polymerization of a vinyl monomer in the presence of a [3]rotaxane-type cross-linker having two radically polymerizable groups. The [3]rotaxane-type cross-linker was prepared in 93 % yield by the typical rotaxane-forming reaction using a dumbbell-shaped aromatic disulfide possessing a bis(ammonium salt) moiety and a crown ether wheel tethered by a hydroxymethyl group (96 %) and the subsequent vinyl group-endowment (80 %). The radical polymerization of methyl methacrylate (MMA) in the presence of the cross-linker (0.1 mol %) at 60 °C afforded solvent-insoluble polymer in 90 % yield. When the polymer was swollen to a gel in dimethylformamide (DMF) and a small part of the gel was UV-irradiated, the gel was promptly solubilized, probably via the photochemical scission of the S–S linkage of the interlocked aromatic disulfide, causing the efficient decomposition of the rotaxane cross-links. The recovered poly(methyl methacrylate) bearing a small amount of crown ether moiety has a molecular weight of Mn 170 kg/mol (Mw/Mn 2.1) that indicated the occurrence of the site-selective photodegradation.

scholarly journals Different structural states of a microtubule cross-linking molecule, captured by quick-freezing motile axostyles in protozoa.

1986 ◽  
Vol 103 (6) ◽  
pp. 2209-2227 ◽  
Author(s):  
J E Heuser
Keyword(s):  
Active Role ◽  
Longitudinal Shear ◽  
The Other ◽  
Cross Bridge ◽  
Other Hand ◽  
Quick Freezing ◽  
Cross Links ◽  
Dynein Arms ◽  
The Cross ◽  
Cross Bridges

Freeze-etch preparation of the laminated bundles of microtubules in motile axostyles demonstrates that the cross-bridges populating individual layers or laminae are structurally similar to the dynein arms of cilia and flagellae. Also, like dynein, they are extracted by high salt and undergo a change in tilt upon removal of endogenous ATP (while the axostyle as a whole straightens and becomes stiff). On the other hand, the bridges running between adjacent microtubule laminae in the axostyle turn out to be much more delicate and wispy in appearance, and display no similarity to dynein arms. Thus we propose that the internal or "intra-laminar" cross-bridges are the active force-generating ATPases in this system, and that they generate overall bends or changes in the helical pitch of the axostyle by altering the longitudinal and lateral register of microtubules in each lamina individually; e.g., by "warping" each lamina and creating longitudinal shear forces within it. The cross-links between adjacent laminae, on the other hand, would then simply be force-transmitting elements that serve to translate the shearing forces generated within individual laminae into overall helical shape changes. (This hypothesis differs from the views of earlier workers who considered a more active role for the later cross-links, postulating that they cause an active sliding between adjacent layers that somehow leads to axostyle movement.) Also described here are physical connections between adjacent intra-laminar cross-bridges, structurally analogous to the overlapping components of the outer dynein arms of cilia and flagella. As with dynein, these may represent a mechanism for propagating local changes from cross-bridge to cross-bridge down the axostyle, as occurs during the passage of bends down the length of the organelle.

scholarly journals Peptidoglycan synthesis in Bacillus licheniformis. The inhibition of cross-linking by benzylpenicillin and cephaloridine in vivo accompanied by the formation of soluble peptidoglycan

1975 ◽  
Vol 146 (1) ◽  
pp. 253-267 ◽  
Author(s):  
Z Tynecka ◽  
J B Ward
Keyword(s):  
Cell Wall ◽  
Bacillus Licheniformis ◽  
Cross Linking ◽  
Cross Links ◽  
Increased Sensitivity ◽  
Cross Bridges ◽  
Chain Lengths ◽  
Soluble Material ◽  
Subsequent Addition

The synthesis of peptidoglycan by an autolysin-deficient β-lactamase-negative mutant of Bacillus licheniformis was studied in vivo in the absence of protein synthesis. Benzylpenicillin and cephaloridine inhibited the formation of cross-bridges between newly synthesized peptidoglycan and the pre-existing cell wall. This inhibition, detected by measurement of the incorporation of N-acetyl[14C]glucosamine into the glycan fraction of the cell wall, was reversed by treatment with β-lactamase and washing. Inhibition of D-alanine carboxypeptidase by benzylpenicillin was not reversed under similar conditions. Cells in which the initial penicillin inhibition of transpeptidation had been reversed showed an increased sensitivity to a subsequent addition of the antibiotic. Chemical analysis of peptidoglycan synthesized after reversal of penicillin inhibition revealed the presence of excess of alanine resulting from the continued inhibition of D-alanine carboxypeptidase. When the cell walls were digested to yield muropeptides so that the degree of cross-linking could be measured, the product after reversal of penicillin inhibition contained fewer cross-links than did the control preparation. Cultures treated with benzylpenicillin and cephaloridine continued to synthesize uncross-linked soluble peptidoglycan, which accumulated in the medium. This soluble material was all newly synthesized peptidoglycan and did not result from autolysis of the bacteria. The average chain lengths of the glycan synthesized in vivo and released as soluble peptidoglycan in the presence of both benzylpenicillin and cephaloridine were similar to those found previously in this organism.

scholarly journals Effect of the Cross-Linking Density on the Swelling and Rheological Behavior of Ester-Bridged β-Cyclodextrin Nanosponges

Materials ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 478
Author(s):  
Gjylije Hoti ◽  
Fabrizio Caldera ◽  
Claudio Cecone ◽  
Alberto Rubin Pedrazzo ◽  
Anastasia Anceschi ◽  
...  
Keyword(s):  
Scale Up ◽  
Future Application ◽  
Cross Linking ◽  
Synthesis Reaction ◽  
Dependent Behavior ◽  
Cyclodextrin Nanosponges ◽  
Potential Applications ◽  
Cross Linker ◽  
The Cross ◽  
Shed Light

The cross-linking density influences the physicochemical properties of cyclodextrin-based nanosponges (CD-NSs). Although the effect of the cross-linker type and content on the NSs performance has been investigated, a detailed study of the cross-linking density has never been performed. In this contribution, nine ester-bridged NSs based on β-cyclodextrin (β-CD) and different quantities of pyromellitic dianhydride (PMDA), used as a cross-linking agent in stoichiometric proportions of 2, 3, 4, 5, 6, 7, 8, 9, and 10 moles of PMDA for each mole of CD, were synthesized and characterized in terms of swelling and rheological properties. The results, from the swelling experiments, exploiting Flory–Rehner theory, and rheology, strongly showed a cross-linker content-dependent behavior. The study of cross-linking density allowed to shed light on the efficiency of the synthesis reaction methods. Overall, our study demonstrates that by varying the amount of cross-linking agent, the cross-linked structure of the NSs matrix can be controlled effectively. As PMDA βCD-NSs have emerged over the years as a highly versatile class of materials with potential applications in various fields, this study represents the first step towards a full understanding of the correlation between their structure and properties, which is a key requirement to effectively tune their synthesis reaction in view of any specific future application or industrial scale-up.

scholarly journals Microtubules and microtubule-associated proteins from the nematode Caenorhabditis elegans: periodic cross-links connect microtubules in vitro.

1986 ◽  
Vol 103 (1) ◽  
pp. 23-31 ◽  
Author(s):  
E J Aamodt ◽  
J G Culotti
Keyword(s):  
Caenorhabditis Elegans ◽  
Apparent Molecular Weight ◽  
Cross Link ◽  
Nematode Caenorhabditis Elegans ◽  
Microtubule Associated Proteins ◽  
C Elegans ◽  
Associated Proteins ◽  
Cross Links ◽  
The Cross

The nematode Caenorhabditis elegans should be an excellent model system in which to study the role of microtubules in mitosis, embryogenesis, morphogenesis, and nerve function. It may be studied by the use of biochemical, genetic, molecular biological, and cell biological approaches. We have purified microtubules and microtubule-associated proteins (MAPs) from C. elegans by the use of the anti-tumor drug taxol (Vallee, R. B., 1982, J. Cell Biol., 92:435-44). Approximately 0.2 mg of microtubules and 0.03 mg of MAPs were isolated from each gram of C. elegans. The C. elegans microtubules were smaller in diameter than bovine microtubules assembled in vitro in the same buffer. They contained primarily 9-11 protofilaments, while the bovine microtubules contained 13 protofilaments. The principal MAP had an apparent molecular weight of 32,000 and the minor MAPs were 30,000, 45,000, 47,000, 50,000, 57,000, and 100,000-110,000 mol wt as determined by SDS-gel electrophoresis. The microtubules were observed, by electron microscopy of negatively stained preparations, to be connected by stretches of highly periodic cross-links. The cross-links connected the adjacent protofilaments of aligned microtubules, and occurred at a frequency of one cross-link every 7.7 +/- 0.9 nm, or one cross-link per tubulin dimer along the protofilament. The cross-links were removed when the MAPs were extracted from the microtubules with 0.4 M NaCl. The cross-links then re-formed when the microtubules and the MAPs were recombined in a low salt buffer. These results strongly suggest that the cross-links are composed of MAPs.

EXPERIMENTAL VALIDATION OF THE CHARLESBY AND HORIKX MODELS APPLIED TO DE-VULCANIZATION OF SULFUR AND PEROXIDE VULCANIZATES OF NR AND EPDM

2016 ◽  
Vol 89 (4) ◽  
pp. 671-688 ◽  
Author(s):  
M. A. L. Verbruggen ◽  
L. van der Does ◽  
W. K. Dierkes ◽  
J. W. M. Noordermeer
Keyword(s):  
Experimental Validation ◽  
Main Chain ◽  
Sol Gel ◽  
Chain Scission ◽  
Cross Linking ◽  
Cross Link ◽  
Practical Reality ◽  
Cross Links ◽  
The Cross ◽  
Theoretical Considerations

ABSTRACT The theoretical model developed by Charlesby to quantify the balance between cross-links creation of polymers and chain scission during radiation cross-linking and further modifications by Horikx to describe network breakdown from aging were merged to characterize the balance of both types of scission on the development of the sol content during de-vulcanization of rubber networks. There are, however, disturbing factors in these theoretical considerations vis-à-vis practical reality. Sulfur- and peroxide-cured NR and EPDM vulcanizates were de-vulcanized under conditions of selective cross-link and random main-chain scissions. Cross-link scission was obtained using thiol-amine reagents for selective cleavage of sulfur cross-links. Random main-chain scission was achieved by heating peroxide vulcanizates of NR with diphenyldisulfide, a method commonly employed for NR reclaiming. An important factor in the analyses of these experiments is the cross-linking index. Its value must be calculated using the sol fraction of the cross-linked network before de-vulcanization to obtain reliable results. The values for the cross-linking index calculated with sol-gel data before de-vulcanization appear to fit the experimentally determined modes of network scission during de-vulcanization very well. This study confirms that the treatment of de-vulcanization data with the merged Charlesby and Horikx models can be used satisfactorily to characterize the de-vulcanization of NR and EPDM vulcanizates.

scholarly journals Protein of insect sperm mitochondrial crystals. Crystallomitin.

1977 ◽  
Vol 73 (3) ◽  
pp. 594-600 ◽  
Author(s):  
B Baccetti ◽  
R Dallai ◽  
V Pallini ◽  
F Rosati ◽  
B A Afzelius
Keyword(s):  
Sodium Dodecyl Sulfate ◽  
Sodium Dodecyl ◽  
Dodecyl Sulfate ◽  
Filament Bundles ◽  
Cross Links ◽  
Insect Sperm ◽  
Main Period ◽  
20 Nm ◽  
Derivatives Of

Mitochondrial derivatives of insect sperm usually contain a crystalline protein that shows a 45-nm main period, made up of 20-nm subperiods, determined by the coiling of filament bundles. Filaments are 2 nm thick and have a globular appearance. The crystals contain two main polypeptides, 52,000 and 55,000 daltons. These polypeptides are closely related, contain a high percentage of proline, and are insoluble in sodium dodecyl sulfate due to disulfide cross links. We suggest for this class of protein the name crystallomitin.

scholarly journals Effects of Current on Arc Fabrication of Cu Nanoparticles

2010 ◽  
Vol 2010 ◽  
pp. 1-5 ◽  
Author(s):  
M. Z. Kassaee ◽  
F. Buazar ◽  
E. Motamedi
Keyword(s):  
Thermal Stability ◽  
Distilled Water ◽  
Face Centered Cubic ◽  
Cu Nanoparticles ◽  
Dta Analysis ◽  
Face Centered ◽  
Average Size ◽  
20 Nm ◽  
Thermal Stability Of ◽  
Sem Analyses

Arc-fabricated copper nanoparticles (Cu Nps) size, morphology and the crystalline structure, as well as the yields of Nps appear sensitive to the applied currents (50–160 A) in distilled water. The results indicate that the sizes of Cu Nps are directly proportional to the currents employed. At 50 A, TEM, XRD, and SEM analyses show fabrication of relatively purest, the most dispersed, face-centered cubic (fcc) brown Cu Nps with rather smallest average size of 20 nm. At the same current, the TGA-DTA analysis reveals neither weight loss nor gain, indicating thermal stability of the fabricated Cu Nps.

scholarly journals Bound (“Glassy”) Rubber as a Free Radical Cross-linked Rubber Layer on a Carbon Black

Materials ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 1992 ◽  
Author(s):  
Alexey Kondyurin ◽  
Anastasia Eliseeva ◽  
Alexander Svistkov
Keyword(s):  
Free Radical ◽  
Carbon Black ◽  
Ion Beam ◽  
Cross Linking ◽  
Carbon Filler ◽  
Free Radical Reactions ◽  
Rubber Layer ◽  
Ion Beam Implantation ◽  
Cross Links ◽  
The Cross

A model of rubber with a cross-linked rubber layer on a carbon black filler has been proposed. The cross-links are the result of free radical reactions generated by carbon atoms with unpaired electrons at the edge of graphitic sheets in a carbon black filler. The experimental study of the cross-linking reactions in polyisoprene was done on a flat carbonized surface after ion beam implantation. The cross-linking process in the polyisoprene macromolecules between two particles was simulated. The model with a cross-linked rubber layer on a carbon filler as a “glassy layer” explains the mechanical properties of the rubber materials.

scholarly journals Synthesis, Characterization of a New Polyacrylic Acid Superabsorbent, Some Heavy Metal Ion Sorption, the Adsorption Isotherms, and Quantum Chemical Investigation

Materials ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 4390
Author(s):  
Sevil Savaskan Yilmaz ◽  
Nuri Yildirim ◽  
Murat Misir ◽  
Yasin Misirlioglu ◽  
Emre Celik
Keyword(s):  
Heavy Metal ◽  
Quantum Chemical ◽  
Metal Ion ◽  
Molecular Mechanic ◽  
Ion Concentration ◽  
Heavy Metal Ion ◽  
Competitive Sorption ◽  
Cross Linker ◽  
The Cross

Poly(acrylic acid/Kryptofix 23-Dimethacrylate) superabsorbent polymer [P (AA/Kry23-DM) SAP] was synthesized by solution polymerization to remove Co, Ni, Cu, Cd, Mn, Zn, Pb, Cr, and Fe ions in water and improve the quality of the water. Kry23-DM cross-linker (1,4,7,13,16-Pentaoxa-10,19 diazo cyclohexene icosane di methacrylate) was synthesized using Kry23 and methacryloyl chloride. The characterization of the molecules was done by FTIR, TGA, DSC, and SEM techniques. The effects of parameters such as pH, concentration, and the metal ion interaction on the heavy metal ions uptaking of SAP was investigated. It was observed that P (AA/Kry23-DM) SAP has maximum water absorption, and the absorption increases with the pH increase. Adsorption rates and sorption capacity, desorption ratios, competitive sorption (qcs), and distribution coefficient (log D) of P(AA/Kry23-DM) SAP were studied as a function of time and pH with the heavy metal ion concentration. Langmuir and Freundlich isotherms of the P (AA/Kry23-DM) SAP were investigated to verify the metal uptake. Molecular mechanic (MM2), Assisted Model Building with Energy Refinement (AMBER), and optimized potentials for liquid simulations (OPLS) methods. were used in quantum chemical calculations for the conformational analysis of the cross-linker and the SAP. ΔH0f calculations of the cross-linker and the superabsorbent were made using Austin Model 1(AM1) method.

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