scholarly journals Calcium-induced aggregation of archaeal bipolar tetraether liposomes derived from the thermoacidophilic archaeonSulfolobus acidocaldarius

Archaea ◽  
2003 ◽  
Vol 1 (3) ◽  
pp. 175-183 ◽  
Author(s):  
Roby Kanichay ◽  
Lawrence T. Boni ◽  
Peter H. Cooke ◽  
Tapan K. Khan
Keyword(s):  
Surface Potential ◽  
Membrane Surface ◽  
Lipid Fraction ◽  
Freeze Fracture ◽  
Correlation Spectroscopy ◽  
Small Unilamellar Vesicles ◽  
Lipid Conformation ◽  
Freeze Fracture Electron Microscopy ◽  
Induced Aggregation ◽  
Fracture Electron

Previously, we showed that the proton permeability of small unilamellar vesicles (SUVs) composed of polar lipid fraction E (PLFE) from the thermoacidophilic archaeonSulfolobus acidocaldariuswas remarkably low and insensitive to temperature (Komatsu and Chong 1998). In this study, we used photon correlation spectroscopy to investigate the time dependence of PLFE SUV size as a function of Ca2+concentration. In the absence of Ca2+, vesicle diameter changed little over 6 months. Addition of Ca2+, however, immediately induced formation of vesicle aggregates with an irregular shape, as revealed by confocal fluorescence microscopy. Aggregation was reversible upon addition of EDTA; however, the reversibility varied with temperature as well as incubation time with Ca2+. Freeze-fracture electron microscopy showed that, after a long period of incubation (2 weeks) with Ca2+, the PLFE vesicles had not just aggregated, but had fused or coalesced. The initial rate of vesicle aggregation varied sigmoidally with Ca2+concentration. At pH 6.6, the threshold calcium concentration (Cr) for vesicle aggregation at 25 and 40 °C was 11 and 17 mM, respectively. At pH 3.0, theCrat 25 °C increased to 25 mM. The temperature dependence ofCrmay be attributable to changes in membrane surface potential, which was –22.0 and –13.2 mV at 25 and 40 °C, respectively, at pH 6.6, as determined by 2-(p-toluidinyl)naphthalene-6-sulfonic acid fluorescence. The variation in surface potential with temperature is discussed in terms of changes in lipid conformation and membrane organization.

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.

scholarly journals Freeze-fracture Electron Microscopy on Microbubbles Used as Theranostics or Made of Lung Surfactant

2010 ◽  
Vol 16 (S2) ◽  
pp. 1172-1173
Author(s):  
B Papahadjopoulos-Sternberg ◽  
J Ackrell
Keyword(s):  
Electron Microscopy ◽  
Lung Surfactant ◽  
Freeze Fracture ◽  
Freeze Fracture Electron Microscopy ◽  
Fracture Electron

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

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.

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