A gradient in the density of intramembrane particles is formed during capping induced by concanavalin A

1986 ◽  
Vol 83 (1) ◽  
pp. 61-76
Author(s):  
H. Bennett ◽  
J. Condeelis
Keyword(s):  
Cell Polarity ◽  
Concanavalin A ◽  
Freeze Fracture ◽  
Integral Membrane Proteins ◽  
Asymmetric Distribution ◽  
Numerical Density ◽  
Ion Currents ◽  
Ion Pumps ◽  
Intramembrane Particles ◽  
The Difference

During capping of concanavalin A (ConA) by amoebae of Dictyostelium discoideum, each cell becomes polarized, with the ConA at one end and newly extended pseudopodia at the opposite end of the cell. This new polarity is stable until the cap is shed or internalized. Intramembrane particles (IMPs) are widely believed to represent large integral membrane proteins, many of which are ion pumps and channels. Since asymmetric ion currents have been implicated in the development of cell polarity, we have used morphological landmarks associated with the capped cells in freeze-fracture to make a morphometric analysis of the IMP distribution relative to the axis of polarization of the capped cell. Untreated cells in suspension extend pseudopodia randomly from their surfaces. In these cells the numerical density of IMPs is random. However, capped cells demonstrate a density gradient of IMPs with the lowest density usually in the pseudopodia and the highest in the cap. The difference in density between the cap and other regions of the cell is two- to threefold for all IMPs, but can be as much as sevenfold for greater than 12 nm IMPs. This study is the first to document that the numerical density of IMPs is altered in response to ligand-induced capping and demonstrates that the distribution of IMPs in a capped cell is related to the axis of polarization of the cell. These results suggest that the development of cell polarity during capping in Dictyostelium amoebae may be due to the asymmetric distribution of IMPs, which may cause asymmetric ion currents across the cell.

Image Analysis of Intramembrane Particles in Freeze-Fractured Biomembranes Using Computer Simulation Techniques

1975 ◽  
Vol 33 ◽  
pp. 214-215
Author(s):  
D.J. Benefiel ◽  
R.S. Weinstein
Keyword(s):  
Membrane Proteins ◽  
Freeze Fracture ◽  
Integral Membrane Proteins ◽  
Systematic Evaluation ◽  
Intramembrane Particles ◽  
Modeling Methods ◽  
Simulation Techniques ◽  
Freeze Fracture Electron Microscopy ◽  
Fracture Electron ◽  
Computer Simulation Techniques

Intramembrane particles (IMP or MAP) are components of most biomembranes. They are visualized by freeze-fracture electron microscopy, and they probably represent replicas of integral membrane proteins. The presence of MAP in biomembranes has been extensively investigated but their detailed ultrastructure has been largely ignored. In this study, we have attempted to lay groundwork for a systematic evaluation of MAP ultrastructure. Using mathematical modeling methods, we have simulated the electron optical appearances of idealized globular proteins as they might be expected to appear in replicas under defined conditions. By comparing these images with the apearances of MAPs in replicas, we have attempted to evaluate dimensional and shape distortions that may be introduced by the freeze-fracture technique and further to deduce the actual shapes of integral membrane proteins from their freezefracture images.

Molecular cytochemistry of freeze-fractured cells

1986 ◽  
Vol 44 ◽  
pp. 894-897
Author(s):  
Pedro Pinto da Silva
Keyword(s):  
Membrane Proteins ◽  
Membrane Surface ◽  
Freeze Fracture ◽  
Biological Membranes ◽  
Bilayer Membrane ◽  
Integral Membrane Proteins ◽  
Distilled Water ◽  
Intramembrane Particles ◽  
Freeze Etching

I will describe four approaches that combine cytochemistry with freeze-fracture: 1) FREEZE-ETCHING; 2) FRACTURE-LABEL; 3) FRACTURE-PERMEATION; and 4) LABEL-FRACTURE. These techniques, in particular fracture-label, involve delicate points of interpretation and numerous validating controls. In the publications listed at the end, these issues have been addressed in detail.1. FREEZE-ETCHING. I developed freeze-etching as a cytochemical approach to prove that membranes were split by freeze-fracture and to show that biological membranes were comprised of a bilayer membrane continuum interrupted by integral membrane proteins.1 - 4 In freeze-etching, the distribution of the marker over the membrane surface exposed by sublimation is compared to that of the intramembrane particles exposed by fracture. It is often required to aggregate the particles into domains larger than the labeling molecules (Fig. 1). This, and the need for freezing in distilled water, severely limits the application of freeze-etching.

Local shadow angle and heights of intramembrane particles in freeze-fracture replicas of proteoliposomes

1986 ◽  
Vol 44 ◽  
pp. 214-215
Author(s):  
M. J. Costello ◽  
G. Gomez
Keyword(s):  
Electron Microscope ◽  
Membrane Proteins ◽  
Inclination Angle ◽  
Freeze Fracture ◽  
Integral Membrane Proteins ◽  
Irregular Surfaces ◽  
Intramembrane Particles ◽  
Aqueous Suspensions ◽  
Microscope Stage

The heights of intramembrane particles (IMPs) produced by integral membrane proteins are difficult to obtain because the local shadow angle in the vicinity of the IMPs is not known for typical freeze-fracture experiments. Even though the average shadow inclination angle is set by the operator (usually 20°-45°), fractures normally produce very irregular surfaces. We have devised a procedure for determining the local shadow angle in selected spherical proteoliposomes from which IMP heights can be calculated. The procedure is an extension of a method to determine the true diameter of vesicles in freeze-cleaved aqueous suspensions and relies on the use of a tiltrotation electron microscope stage.

scholarly journals Regionalization of transmembrane glycoproteins in the plasma membrane of boar sperm head is revealed by fracture-label.

1983 ◽  
Vol 97 (5) ◽  
pp. 1356-1364 ◽  
Author(s):  
A P Aguas ◽  
P Pinto da Silva
Keyword(s):  
Plasma Membrane ◽  
Binding Sites ◽  
Freeze Fracture ◽  
Transmembrane Proteins ◽  
Integral Membrane Proteins ◽  
Drastic Reduction ◽  
Intramembrane Particles ◽  
And Topology ◽  
Boar Sperm ◽  
Parallel Distribution

We used fracture-label and surface labeling techniques to characterize the distribution and topology of wheat germ agglutinin (WGA) receptors in the plasma membrane of boar sperm heads. We show that freeze-fracture results in preferential, but not exclusive, partition of WGA-binding sites with the outer (exoplasmic) half of the plasma membrane. Labeling of the inner (protoplasmic) half of the membrane is significant, and is denser over the areas that overlie the acrosome. Exoplasmic membrane halves are uniformly labeled. Analysis of freeze-fracture replicas revealed that the distribution of intramembrane particles over protoplasmic faces parallels that of WGA-binding sites as observed by fracture-label. Coating of intact spermatozoa with cationized ferritin results in drastic reduction of the labeling of both protoplasmic and exoplasmic membrane halves. Labeling of sperm cells lysed by short hypotonic shock fails to reveal the presence of WGA-binding sites at the inner surface of the plasma membrane. We conclude that: (a) all WGA-binding glycoconjugates are exposed at the outer surface of the membrane; (b) some of these glycoconjugates correspond to transmembrane glycoproteins that, on fracture, partition with the inner half of the membrane; (c) these transmembrane proteins are accumulated in the region of the plasma membrane that overlies the acrosome; and (d) parallel distribution of intramembrane particles and WGA-binding glycoproteins provides renewed support for the view of particles as the morphological counterpart of integral membrane proteins.

Heterogeneity of Size and Distribution of Intramembrane Particles in the Plasma Membrane of Yeast

1977 ◽  
Vol 35 ◽  
pp. 596-597
Author(s):  
E. Keyhani
Keyword(s):  
Plasma Membrane ◽  
Candida Utilis ◽  
Synthetic Medium ◽  
Freeze Fracture ◽  
Translational Diffusion ◽  
Yeast Cells ◽  
Distilled Water ◽  
Intramembrane Particles ◽  
The Matrix ◽  
Water Cell

The matrix of biological membranes consists of a lipid bilayer into which proteins or protein aggregates are intercalated. Freeze-fracture techni- ques permit these proteins, perhaps in association with lipids, to be visualized in the hydrophobic regions of the membrane. Thus, numerous intramembrane particles (IMP) have been found on the fracture faces of membranes from a wide variety of cells (1-3). A recognized property of IMP is their tendency to form aggregates in response to changes in experi- mental conditions (4,5), perhaps as a result of translational diffusion through the viscous plane of the membrane. The purpose of this communica- tion is to describe the distribution and size of IMP in the plasma membrane of yeast (Candida utilis).Yeast cells (ATCC 8205) were grown in synthetic medium (6), and then harvested after 16 hours of culture, and washed twice in distilled water. Cell pellets were suspended in growth medium supplemented with 30% glycerol and incubated for 30 minutes at 0°C, centrifuged, and prepared for freeze-fracture, as described earlier (2,3).

scholarly journals Investigating the properties of a galaxy group at z = 0.6

2020 ◽  
Vol 15 (S359) ◽  
pp. 188-189
Author(s):  
Daniela Hiromi Okido ◽  
Cristina Furlanetto ◽  
Marina Trevisan ◽  
Mônica Tergolina
Keyword(s):  
Large Scale ◽  
The Other ◽  
Numerical Density ◽  
Spectroscopy Data ◽  
Stellar Kinematics ◽  
Galaxy Groups ◽  
The Galaxy ◽  
The Difference ◽  
The Impact ◽  
The Universe

AbstractGalaxy groups offer an important perspective on how the large-scale structure of the Universe has formed and evolved, being great laboratories to study the impact of the environment on the evolution of galaxies. We aim to investigate the properties of a galaxy group that is gravitationally lensing HELMS18, a submillimeter galaxy at z = 2.39. We obtained multi-object spectroscopy data using Gemini-GMOS to investigate the stellar kinematics of the central galaxies, determine its members and obtain the mass, radius and the numerical density profile of this group. Our final goal is to build a complete description of this galaxy group. In this work we present an analysis of its two central galaxies: one is an active galaxy with z = 0.59852 ± 0.00007, while the other is a passive galaxy with z = 0.6027 ± 0.0002. Furthermore, the difference between the redshifts obtained using emission and absorption lines indicates an outflow of gas with velocity v = 278.0 ± 34.3 km/s relative to the galaxy.

scholarly journals Studies on the orientation of brush-border membrane vesicles

1978 ◽  
Vol 172 (1) ◽  
pp. 57-62 ◽  
Author(s):  
W Haase ◽  
A Schäfer ◽  
H Murer ◽  
R Kinne
Keyword(s):  
Brush Border ◽  
Brush Border Membrane ◽  
Rat Kidney ◽  
Freeze Fracture ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Immunological Methods ◽  
Kidney Cortex ◽  
Asymmetric Distribution ◽  
Rat Kidney Cortex

Orientation of rat renal and intestinal brush-border membrane vesicles was studied with two independent methods: electron-microscopic freeze-fracture technique and immunological methods. With the freeze-fracture technique a distinct asymmetric distribution of particles on the two membrane fracture faces was demonstrated; this was used as a criterion for orientation of the isolated membrane vesicles. For the immunological approach the accessibility or inaccessibility of aminopeptidase M localized on the outer surface of the cell membrane to antibodies was used. With both methods we showed that the brush-border membrane vesicles isolated from rat kidney cortex and from rat small intestine for transport studies are predominantly orientated right-side out.

Ultrastructural analysis of the apical ectodermal ridge during vertebrate limb morphogenesis

Development ◽  
1977 ◽  
Vol 41 (1) ◽  
pp. 223-232
Author(s):  
John F. Fallon ◽  
Robert O. Kelley
Keyword(s):  
Electron Microscopy ◽  
Gap Junctions ◽  
Freeze Fracture ◽  
Apical Ectodermal Ridge ◽  
Structural Requirements ◽  
Limb Morphogenesis ◽  
Vertebrate Limb ◽  
The Difference ◽  
Freeze Fracture Electron Microscopy ◽  
Fracture Electron

The fine structure of the apical ectodermal ridge of five phylogenetically divergent orders of mammals and two orders of birds was examined using transmission and freeze fracture electron microscopy. Numerous large gap junctions were found in all apical ectodermal ridges studied. This was in contrast to the dorsal and ventral limb ectoderms where gap junctions were always very small and sparsely distributed. Thus, gap junctions distinguish the inductively active apical epithelium from the adjacent dorsal and ventral ectoderms. The distribution of gap junctions in the ridge was different between birds and mammals but characteristic within the two classes. Birds, with a pseudostratified columnar apical ridge, had the heaviest concentration of gap junctions at the base of each ridge cell close to the point where contact was made with the basal lamina. Whereas mammals, with a stratified cuboidal to squamous apical ridge, had a more uniform distribution of gap junctions throughout the apical epithelium. The difference in distribution for each class may reflect structural requirements for coupling of cells in the entire ridge. We propose that all cells of the apical ridges of birds and mammals are electrotonically and/or metabolically coupled and that this may be a requirement for the integrated function of the ridge during limb morphogenesis.

Differences in density of Concanavalin A-binding sites due to differences in surface morphology of suspended normal and transformed 3T3 fibroblasts

1975 ◽  
Vol 19 (1) ◽  
pp. 21-32
Author(s):  
J.G. Collard ◽  
J.H. Temmink
Keyword(s):  
Surface Morphology ◽  
Concanavalin A ◽  
Binding Sites ◽  
3T3 Cells ◽  
Con A ◽  
3T3 Fibroblasts ◽  
Transformed Fibroblasts ◽  
Transmission Electron ◽  
The Difference ◽  
Electron Microscopes

Calculations of the density of Concanavalin A (Con A)-binding sites on normal and transformed fibroblasts have, as yet, been based on the unproven assumption that suspended cells are smooth spheres. We studied the surface morphology of suspended normal and transformed fibroblasts with scanning and transmission electron microscopes, and found a large difference in surface morphology between suspended normal and transformed 3T3 cells. When this difference in surface morphology was taken into account, the estimated cell surface area of normal 3T3 cells was approximately seven times larger than that of transformed 3T3 cells. Since equal numbers of 3H-Con A molecules are bound on normal and transformed cells, the density of Con A-binding sites is approximately seven times greater on transformed than on normal 3T3 cells. The difference in density of Con A-binding sites between normal and transformed fibroblasts might be sufficient to explain the difference in agglutination response, as originally suggested by Burger, and may also be the cause of the different degrees of clustering of Con A-binding sites on the plasma membrane of these cells.

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