Cleavage and brittle fracture in GaAs: Indication of lattice dynamic instability on the nanometer scale

1997 ◽  
Vol 38 (9) ◽  
pp. 675-680 ◽  
Author(s):  
M. A Rosentreter ◽  
M Wenderoth ◽  
N. H Theuerkauf ◽  
A. J Heinrich ◽  
M. A Schneider ◽  
...  
Keyword(s):  
Brittle Fracture ◽  
Dynamic Instability ◽  
Lattice Dynamic ◽  
Nanometer Scale

The microtubule lattice — dynamic instability of concepts

1995 ◽  
Vol 5 (7) ◽  
pp. 262-266 ◽  
Author(s):  
Eckhard Mandelkow ◽  
Young-Hwa Song ◽  
Eva-Maria Mandelkow
Keyword(s):  
Dynamic Instability ◽  
Lattice Dynamic

Nonlinear dynamic instability in brittle fracture of GaAs

1999 ◽  
Vol 60 (7) ◽  
pp. 4789-4795 ◽  
Author(s):  
K. Sauthoff ◽  
M. Wenderoth ◽  
A. J. Heinrich ◽  
M. A. Rosentreter ◽  
K. J. Engel ◽  
...  
Keyword(s):  
Brittle Fracture ◽  
Nonlinear Dynamic ◽  
Dynamic Instability

scholarly journals Distinct Protofilament-scale Dynamics Define the Differential Remodeling of Microtubule Arrays

2020 ◽  
Author(s):  
S. S. Wijeratne ◽  
M. Marchan ◽  
J. S. Tresback ◽  
R. Subramanian
Keyword(s):  
Electron Microscopy ◽  
Large Scale ◽  
Dynamic Instability ◽  
Lattice Defect ◽  
Nanometer Scale ◽  
Force Microscopy ◽  
Atomic Force ◽  
Length Regulation ◽  
Intrinsic Dynamic ◽  
Powerful Strategy

SUMMARYThe intrinsic dynamic instability of microtubules and their control by associated enzymes, such as depolymerases, are essential for the organization of complex multi-microtubule arrays like spindle and axoneme. However, existing optical or electron-microscopy methods lack the spatial-temporal resolution to observe the dynamics of individual microtubules within arrays. We use Atomic Force Microscopy (AFM) to image depolymerizing arrays at single microtubule and protofilament resolution. We discover previously unseen modes of microtubule destabilization by conserved depolymerases. The kinesin-13 MCAK mediates asynchronous protofilament depolymerization and lattice-defect propagation, whereas the kinesin-8 Kip3p promotes synchronous protofilament depolymerization. Unexpectedly, MCAK can depolymerize axonemal doublets but Kip3p cannot. We propose that distinct protofilament-level activities underlie the functional dichotomy of depolymerases, resulting in either large-scale destabilization or length regulation of microtubule arrays. Our work establishes AFM as a powerful strategy to visualize microtubule dynamics and reveals how nanometer-scale substrate specificity leads to differential remodeling of micron-sized cytoskeletal structures.

scholarly journals Mechanisms of kinetic stabilization by the drugs paclitaxel and vinblastine

2017 ◽  
Vol 28 (9) ◽  
pp. 1238-1257 ◽  
Author(s):  
Brian T. Castle ◽  
Seth McCubbin ◽  
Louis S. Prahl ◽  
Jordan N. Bernens ◽  
David Sept ◽  
...  
Keyword(s):  
Self Assembly ◽  
Dynamic Instability ◽  
Molecular Level ◽  
Energy Difference ◽  
Microtubule Assembly ◽  
Live Cells ◽  
Nanometer Scale ◽  
Microtubule Targeting Agents ◽  
Main Effect ◽  
Thermodynamic Basis

Microtubule-targeting agents (MTAs), widely used as biological probes and chemotherapeutic drugs, bind directly to tubulin subunits and “kinetically stabilize” microtubules, suppressing the characteristic self-assembly process of dynamic instability. However, the molecular-level mechanisms of kinetic stabilization are unclear, and the fundamental thermodynamic and kinetic requirements for dynamic instability and its elimination by MTAs have yet to be defined. Here we integrate a computational model for microtubule assembly with nanometer-scale fluorescence microscopy measurements to identify the kinetic and thermodynamic basis of kinetic stabilization by the MTAs paclitaxel, an assembly promoter, and vinblastine, a disassembly promoter. We identify two distinct modes of kinetic stabilization in live cells, one that truly suppresses on-off kinetics, characteristic of vinblastine, and the other a “pseudo” kinetic stabilization, characteristic of paclitaxel, that nearly eliminates the energy difference between the GTP- and GDP-tubulin thermodynamic states. By either mechanism, the main effect of both MTAs is to effectively stabilize the microtubule against disassembly in the absence of a robust GTP cap.

Dynamic Instability of Brittle Fracture

1999 ◽  
Vol 82 (11) ◽  
pp. 2314-2317 ◽  
Author(s):  
Mokhtar Adda-Bedia ◽  
Rodrigo Arias ◽  
Martine Ben Amar ◽  
Fernando Lund
Keyword(s):  
Brittle Fracture ◽  
Dynamic Instability

Analysis of the Mechanism of Microtubule Dynamic Instability Using a UV Microbeam to Sever Elongating Microtubules

1988 ◽  
Vol 46 ◽  
pp. 122-123
Author(s):  
R.A Walker ◽  
S. Inoue ◽  
E.D. Salmon
Keyword(s):  
Dynamic Instability ◽  
Microtubule Dynamic ◽  
Gtp Hydrolysis ◽  
Abrupt Transition ◽  
Microtubule Associated Proteins ◽  
Asymmetrical Structure ◽  
Associated Proteins

Microtubules polymerized in vitro from tubulin purified free of microtubule-associated proteins exhibit dynamic instability (1,2,3). Free microtubule ends exist in persistent phases of elongation or rapid shortening with infrequent, but, abrupt transitions between these phases. The abrupt transition from elongation to rapid shortening is termed catastrophe and the abrupt transition from rapid shortening to elongation is termed rescue. A microtubule is an asymmetrical structure. The plus end grows faster than the minus end. The frequency of catastrophe of the plus end is somewhat greater than the minus end, while the frequency of rescue of the plus end in much lower than for the minus end (4).The mechanism of catastrophe is controversial, but for both the plus and minus microtubule ends, catastrophe is thought to be dependent on GTP hydrolysis. Microtubule elongation occurs by the association of tubulin-GTP subunits to the growing end. Sometime after incorporation into an elongating microtubule end, the GTP is hydrolyzed to GDP, yielding a core of tubulin-GDP capped by tubulin-GTP (“GTP-cap”).

Analyzing reactions of single mechanoenzyme molecules by light microscopy

1992 ◽  
Vol 50 (1) ◽  
pp. 426-427
Author(s):  
Jeff Gelles
Keyword(s):  
Image Processing ◽  
Reaction Mechanisms ◽  
Transient State ◽  
Nanometer Scale ◽  
Reaction Intermediates ◽  
Enzyme Molecule ◽  
Directed Movement ◽  
Enzyme Molecules ◽  
Individual Enzyme ◽  
Single Reaction

Mechanoenzymes are enzymes which use a chemical reaction to power directed movement along biological polymer. Such enzymes include the cytoskeletal motors (e.g., myosins, dyneins, and kinesins) as well as nucleic acid polymerases and helicases. A single catalytic turnover of a mechanoenzyme moves the enzyme molecule along the polymer a distance on the order of 10−9 m We have developed light microscope and digital image processing methods to detect and measure nanometer-scale motions driven by single mechanoenzyme molecules. These techniques enable one to monitor the occurrence of single reaction steps and to measure the lifetimes of reaction intermediates in individual enzyme molecules. This information can be used to elucidate reaction mechanisms and determine microscopic rate constants. Such an approach circumvents difficulties encountered in the use of traditional transient-state kinetics techniques to examine mechanoenzyme reaction mechanisms.

Microstructural characterization of sol-gel coating on PET films

1994 ◽  
Vol 52 ◽  
pp. 886-887
Author(s):  
R. T. Chen ◽  
R.A. Norwood
Keyword(s):  
Ion Beam ◽  
Sol Gel ◽  
Industrial Applications ◽  
Hard Coatings ◽  
Nanometer Scale ◽  
Ion Beam Sputtering ◽  
Process Technology ◽  
Refractive Index Measurement ◽  
Organically Modified ◽  
Pet Films

Sol-gel processing has been used to control the structure of a material on a nanometer scale in preparing advanced ceramics and glasses. Film coating using the sol-gel process was also found to be a viable process technology in applications such as optical, porous, antireflection and hard coatings. In this study, organically modified silicate (Ormosil) coatings are applied to PET films for various industrial applications. Sol-gel materials are known to exhibit nanometer scale structures which havepreviously been characterized by small-angle X-ray scattering (SAXS), neutron scattering and light scattering. Imaging of the ultrafine sol-gel structures has also been performed using an ultrahigh resolution replica/TEM technique. The objective of this study was to evaluate the ultrafine structures inthe sol gel coatings using a direct imaging technique: atomic force microscopy (AFM). In addition, correlation of microstructures with processing parameters, coating density and other physical properties will be discussed.The materials evaluated are organically modified silicate coatings on PET film substrates. Refractive index measurement by the prism coupling method was used to assess density of the sol-gel coating.AFM imaging was performed on a Nanoscope III AFM (by Digital Instruments) using constant force mode. Solgel coating samples coated with a thin layer of Ft (by ion beam sputtering) were also examined by STM in order to confirm the structures observed in the contact type AFM. In addition, to compare the previous results, sol-gel powder samples were also prepared by ultrasonication followed by Pt/Au shadowing and examined using a JEOL 100CX TEM.

Time-Resolved Cryo-Electron Microscopy of Oscillating Microtubules

1990 ◽  
Vol 48 (1) ◽  
pp. 502-503
Author(s):  
Eva-Maria Mandelkow ◽  
Ron Milligan
Keyword(s):  
Electron Microscopy ◽  
Dynamic Instability ◽  
Entire Solution ◽  
Reaction Scheme ◽  
Time Resolved ◽  
X Ray ◽  
X Ray Scattering ◽  
A Chain ◽  
Ray Scattering

Microtubules form part of the cytoskeleton of eukaryotic cells. They are hollow libers of about 25 nm diameter made up of 13 protofilaments, each of which consists of a chain of heterodimers of α-and β-tubulin. Microtubules can be assembled in vitro at 37°C in the presence of GTP which is hydrolyzed during the reaction, and they are disassembled at 4°C. In contrast to most other polymers microtubules show the behavior of “dynamic instability”, i.e. they can switch between phases of growth and phases of shrinkage, even at an overall steady state [1]. In certain conditions an entire solution can be synchronized, leading to autonomous oscillations in the degree of assembly which can be observed by X-ray scattering (Fig. 1), light scattering, or electron microscopy [2-5]. In addition such solutions are capable of generating spontaneous spatial patterns [6].In an earlier study we have analyzed the structure of microtubules and their cold-induced disassembly by cryo-EM [7]. One result was that disassembly takes place by loss of protofilament fragments (tubulin oligomers) which fray apart at the microtubule ends. We also looked at microtubule oscillations by time-resolved X-ray scattering and proposed a reaction scheme [4] which involves a cyclic interconversion of tubulin, microtubules, and oligomers (Fig. 2). The present study was undertaken to answer two questions: (a) What is the nature of the oscillations as seen by time-resolved cryo-EM? (b) Do microtubules disassemble by fraying protofilament fragments during oscillations at 37°C?

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