Bonafide Substructure in the Core of Ferritin

1985 ◽  
Vol 43 ◽  
pp. 322-323
Author(s):  
William H. Massover
Keyword(s):  
Phase Contrast ◽  
Central Cavity ◽  
Amplitude Image ◽  
Ultrastructural Studies ◽  
The Core ◽  
Hydrated Ferric Oxide ◽  
Imaging Artifact ◽  
Contrast Image ◽  
Protein Shell ◽  
Regular Patterns

Each molecule of ferritin (d = 130Å) contains a core of iron surrounded by a 24-subunit protein shell. The amount of iron stored is variable and is present within the central cavity (d = 80Å) as a hydrated ferric oxide equivalent to the mineral, ferrihydrite. Many early ultrastructural studies of ferritin detected regular patterns of a multiparticulate substructure in the iron-rich core [e.g., 3,4], Each small particle was termed a “micelle“; a theory became widely accepted that a core consisted of up to six micelles positioned at the vertices of an octahedron. Other workers recognized that the apparent micelles were smaller or even disappeared if images were recorded closer to exact focus [e.g., 5]. In 1969, Haydon clearly established that the observed substructure was really an imaging artifact; each apparent micelle was only a dot in the underfocused phase contrast image of the supporting film superimposed on the amplitude image of the strongly scattering metal.

Characteristics of an Electrostatic Phase Plate

1972 ◽  
Vol 30 ◽  
pp. 618-619
Author(s):  
William Krakow ◽  
Benjamin Siegel
Keyword(s):  
Phase Contrast ◽  
Objective Lens ◽  
Phase Plate ◽  
Net Charge ◽  
Phase Plates ◽  
Beam Currents ◽  
Contrast Image ◽  
Bright Phase ◽  
Additional Phase Shift ◽  
Additional Phase

Unwin has used a metallized non-conducting thread in the back focal plane of the objective lens that stops out a portion of the unscattered beam, takes on a localized positive charge and thus produces an additional phase shift to give a different transfer function of the lens. Under the particular conditions Unwin used, the phase contrast image was shifted to bright phase contrast for optimum focus.We have investigated the characteristics of this type of electrostatic phase plate, both analytically and experimentally, as functions of the magnitude of charge and defocus. Phase plates have been constructed by using Wollaston wire to mount 0.25μ diameter platinum wires across apertures ranging from 50 to 200μ diameter and vapor depositing SiO and gold on the mounted wires to give them the desired charging characteristics. The net charge was varied by adjusting only the bias on the Wehnelt shield of the gun, and hence the beam currents and effective size of the source.

Evaluation method for imaging plate resolution by means of phase contrast transfer function

1995 ◽  
Vol 53 ◽  
pp. 662-663 ◽  
Author(s):  
T. Oikawa ◽  
H. Kosugi ◽  
F. Hosokawa ◽  
D. Shindo ◽  
M. Kersker
Keyword(s):  
Transfer Function ◽  
Phase Contrast ◽  
Evaluation Method ◽  
Amorphous Film ◽  
Imaging Plate ◽  
X Rays ◽  
Special Shape ◽  
Contrast Transfer Function ◽  
Contrast Image ◽  
Specimen Shape

Evaluation of the resolution of the Imaging Plate (IP) has been attempted by some methods. An evaluation method for IP resolution, which is not influenced by hard X-rays at higher accelerating voltages, was proposed previously by the present authors. This method, however, requires truoblesome experimental preperations partly because specially synthesized hematite was used as a specimen, and partly because a special shape of the specimen was used as a standard image. In this paper, a convenient evaluation method which is not infuenced by the specimen shape and image direction, is newly proposed. In this method, phase contrast images of thin amorphous film are used.Several diffraction rings are obtained by the Fourier transformation of a phase contrast image of thin amorphous film, taken at a large under focus. The rings show the spatial-frequency spectrum corresponding to the phase contrast transfer function (PCTF). The envelope function is obtained by connecting the peak intensities of the rings. The evelope function is offten used for evaluation of the instrument, because the function shows the performance of the electron microscope (EM).

Pathways for penetration of iron and negative stain across the protein shell of ferritin: Ultrastructural perspectives

1992 ◽  
Vol 50 (2) ◽  
pp. 1012-1013
Author(s):  
William H. Massover
Keyword(s):  
Outer Shell ◽  
X Ray Diffraction ◽  
Central Cavity ◽  
X Ray ◽  
Subunit Dissociation ◽  
Negative Stain ◽  
Analogous Question ◽  
Protein Shell

Molecules of the metalloprotein, ferritin, have an outer shell comprised of a polymeric assembly of 24 polypeptide subunits (apoferritin). This protein shell encloses a hydrated space, the central cavity, within which up to several thousand iron atoms can be deposited as the biomineral, ferrihydrite. The actual pathway taken by iron moving across the protein shell is not known; an analogous question exists for the demonstrated entrance of negative stains into the central cavity. Intersubunit interstices at the 4-fold and 3-fold symmetry axes have been defined with x-ray diffraction, and were hypothesized to provide a pathway for penetration through the outer shell; however, since these channels are only 4Å in width, they are much too small to allow simple permeation of either hydrated iron or stain ions. A different hypothesis, based on studies of subunit dissociation from highly diluted ferritin, proposes that transient gaps in the protein shell are created by a rapid reversible subunit release and permit the direct passage of large ions into the central cavity.

scholarly journals Influence of spatial structure on protein damage susceptibility: a bioinformatics approach

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Maximilian Fichtner ◽  
Stefan Schuster ◽  
Heiko Stark
Keyword(s):  
Amino Acids ◽  
Molecular Medicine ◽  
Protein Damage ◽  
Aging Research ◽  
Form And Function ◽  
The Core ◽  
And Function ◽  
Thermophilic Organisms ◽  
Damage Susceptibility ◽  
Protein Shell

AbstractAging research is a very popular field of research in which the deterioration or decline of various physiological features is studied. Here we consider the molecular level, which can also have effects on the macroscopic level. The proteinogenic amino acids differ in their susceptibilities to non-enzymatic modification. Some of these modifications can lead to protein damage and thus can affect the form and function of proteins. For this, it is important to know the distribution of amino acids between the protein shell/surface and the core. This was investigated in this study for all known structures of peptides and proteins available in the PDB. As a result, it is shown that the shell contains less susceptible amino acids than the core with the exception of thermophilic organisms. Furthermore, proteins could be classified according to their susceptibility. This can then be used in applications such as phylogeny, aging research, molecular medicine, and synthetic biology.

scholarly journals Scaling Uncertainty in Visual Perception and Estimation Tasks

2020 ◽  
Author(s):  
Eleanor Brower Schille-Hudson ◽  
David Landy
Keyword(s):  
Social Factors ◽  
Common Source ◽  
Uncertain Information ◽  
Social Significance ◽  
Estimation Task ◽  
The Core ◽  
Bayesian Formulation ◽  
Visual Properties ◽  
The Bayesian Approach ◽  
Regular Patterns

Demographic perception—the perception of social quantities of geopolitical scale and social significance—has been extensivelystudied in cognitive and political science (Citrin & Sides, 2008; Gilens, 2001; Herda, 2013). Regular patterns of over- and under-estimation emerge. Americans greatly overestimate, for instance, the proportion of citizens that identify as gay or Muslim, while underestimating those that are Christian. While these errors have been attributed to social factors such as fear of specific minorities (Gallagher, 2003; Wong, 2007), other work has suggested that these patterns result from the psychophysics of the perception of proportions (Landy, Guay & Marghetis 2018). A Bayesian formulation suggests that biases in the estimation of both social proportions and simple visual properties result from a common source: ‘hedging’ uncertain information toward a prior. Here we present a novel lab paradigm and two experiments that manipulate uncertainty in a simple (dot estimation) task, verifying the core assumptions of the Bayesian approach.

Figurative language in multilingual students’ L2 Swedish – a usage-based perspective

2021 ◽  
Vol 11 (2) ◽  
pp. 235-260
Author(s):  
Julia Prentice
Keyword(s):  
Cognitive Processes ◽  
Figurative Language ◽  
Complex Interplay ◽  
Multilingual Students ◽  
The Core ◽  
Language Class ◽  
Pragmatic Information ◽  
Class Room ◽  
Regular Patterns ◽  
Figurative Expressions

Abstract The aim of the current paper is to reinterpret some results of two previous studies on the mastery of figurative expressions from the perspective of usage-based linguistics. The reanalysis aims to shed more light on the learning and use of figurative language by multilingual students by exploring the complex interplay of linguistic creativity, expressivity, and conventionality in figurative expressions. The reinterpretation shows that many of the examples that were previously categorized as novel figurative expressions used in students’ writing, can be analyzed as instances of regular patterns, i.e. constructions, with certain lexical idiosyncrasies. Modifications of conventionalized figurative expressions are discussed and reinterpreted in terms of strength of entrenchment of links between form and meaning within certain constructions or links between constructions and conventionalized pragmatic information in the multilinguals’ mental construction. Implications for the treatment of Swedish figurative expressions in the second language class room are, in line with previous research, that focusing on regularity might reduce unpredictability, often seen as the core difficulty in the learning of such expressions in an L2. The paper also offers some directions for further investigation of the socio-cognitive processes involved in the learning of figurative language in an additional language.

Experimental verification of phase contrast image synthesis system

1996 ◽  
Author(s):  
Jesper Glueckstad ◽  
Haruyoshi Toyoda ◽  
Narihiro Yoshida ◽  
Tamiki Takemori ◽  
Tsutomu Hara
Keyword(s):  
Experimental Verification ◽  
Phase Contrast ◽  
Image Synthesis ◽  
Phase Contrast Image ◽  
Synthesis System ◽  
Contrast Image

scholarly journals Green Fluorescent Protein and Phase-Contrast Image Fusion via Generative Adversarial Networks

2019 ◽  
Vol 2019 ◽  
pp. 1-11 ◽  
Author(s):  
Wei Tang ◽  
Yu Liu ◽  
Chao Zhang ◽  
Juan Cheng ◽  
Hu Peng ◽  
...  
Keyword(s):  
Phase Contrast ◽  
Fluorescent Protein ◽  
Structural Information ◽  
Generative Adversarial Networks ◽  
Phase Contrast Image ◽  
Functional Information ◽  
Adversarial Networks ◽  
Fused Image ◽  
Green Fluorescent ◽  
Contrast Image

In the field of cell and molecular biology, green fluorescent protein (GFP) images provide functional information embodying the molecular distribution of biological cells while phase-contrast images maintain structural information with high resolution. Fusion of GFP and phase-contrast images is of high significance to the study of subcellular localization, protein functional analysis, and genetic expression. This paper proposes a novel algorithm to fuse these two types of biological images via generative adversarial networks (GANs) by carefully taking their own characteristics into account. The fusion problem is modelled as an adversarial game between a generator and a discriminator. The generator aims to create a fused image that well extracts the functional information from the GFP image and the structural information from the phase-contrast image at the same time. The target of the discriminator is to further improve the overall similarity between the fused image and the phase-contrast image. Experimental results demonstrate that the proposed method can outperform several representative and state-of-the-art image fusion methods in terms of both visual quality and objective evaluation.

X-ray phase contrast image simulation

2007 ◽  
Vol 254 (2) ◽  
pp. 307-318 ◽  
Author(s):  
A. Peterzol ◽  
J. Berthier ◽  
P. Duvauchelle ◽  
C. Ferrero ◽  
D. Babot
Keyword(s):  
Phase Contrast ◽  
Phase Contrast Image ◽  
Image Simulation ◽  
X Ray ◽  
Contrast Image

Neutronics Optimization of UN Fuel Pin Assemblies for a Sodium-Cooled, Small Modular Reactor

2011 ◽  
Author(s):  
Timothy M. Schriener ◽  
Mohamed S. El-Genk
Keyword(s):  
Thermal Power ◽  
Reactor Core ◽  
Central Cavity ◽  
Preliminary Results ◽  
The Core ◽  
Small Modular Reactor ◽  
Fuel Assemblies ◽  
Fuel Pin ◽  
Reference Design ◽  
Centerline Temperature

This paper presents preliminary results of neutronics and thermal-hydraulics design analysis of a sodium cooled, small modular reactor (SMR). The reactor’s nominal thermal power is 150 MWth at sodium inlet and exit temperatures of 630 and 780 K. The reactor core is comprised of three rings of shrouded hexagonal assemblies of 19.8% enriched UN fuel pins and a hexagonal assembly of enriched B4C pins in the central cavity for a coarse reactivity control. The objectives are to provide enough excess reactivity for achieving a refueling cycle > 5 year, maintaining a more even coolant flow in the core assemblies and keeping the peak centerline temperature of UN fuel pins < 1300 K. Fuel assemblies with scalloped shroud walls, 4 rings and 1.942 cm diameter fuel pins with p/d = 1.098 are selected for the reference design of the present SMR. In this design, peak fuel centerline temperature is only 1240 K and the beginning-of-life, cold-clean excess reactivity is $26.67.

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