scholarly journals Observations of membrane fusion in a liposome dispersion: the missing fusion intermediate?

F1000Research ◽  
2015 ◽  
Vol 4 ◽  
pp. 4 ◽  
Author(s):  
Marianna Foldvari
Keyword(s):  
Membrane Fusion ◽  
Freeze Fracture ◽  
Fusion Event ◽  
Electron Microscopic ◽  
Liposome Dispersion ◽  
Liposome Fusion ◽  
Fracture Electron ◽  
Structural Arrangements

Early intermediate structures of liposome-liposome fusion events were captured by freeze-fracture electron microscopic (EM) technique. The images show the morphology of the fusion interface at several different stages of the fusion event. One of the intermediates was captured at a serendipitous stage of two vesicles’ membranes (both leaflets) merging and their contents starting to intermix clearly showing the fusion interface with a previously unseen fusion rim. From the morphological information a hypothetical sequence of the fusion event and corresponding lipid structural arrangements are described.

Studies of membrane fusion. VI. Mechanism of the membrane fusion and cell swelling stages of Sendai virus-mediated cell fusion

1980 ◽  
Vol 43 (1) ◽  
pp. 103-118
Author(s):  
S. Knutton
Keyword(s):  
Membrane Fusion ◽  
Cell Fusion ◽  
Sendai Virus ◽  
Freeze Fracture ◽  
Viral Envelope ◽  
Cell Swelling ◽  
Fusion Event ◽  
Virus Envelope ◽  
Membrane Rupture ◽  
Membrane Tubules

The membrane fusion and cell swelling stages of Sendai virus-mediated cell-cell fusion have been studied by thin-section and freeze-fracture electron microscopy. Sites of membrane fusion have been detected in human erythrocytes arrested at the membrane fusion stage of cell fusion and in virtually all cases a fused viral envelope or envelope components has been identified thus providing further direct evidence that cell-viral envelope-cell bridge formation is the membrane fusion event in Sendai virus-induced cell fusion. Radial expansion of a single virus bridge connecting 2 cells is sufficient to produce a fused cell. Membrane redistribution which occurs during this cell swelling stage of the fusion process is often accompanied by the formation of a system of membrane tubules in the plane of expansion of the virus bridge. The tubules originate from points of fusion between the bridging virus envelope and the erythrocyte membrane and also expand radially as cells swell. Ultimately membrane rupture occurs and the tubules appear to break down as small vesicles. When previously observed in cross-sectioned cells these membrane tubules were interpreted as sites of direct membrane fusion. The present study indicates that this interpretation is incorrect and shows that the tubules are generated subsequent to membrane fusion when 2 cells connected by a virus bridge are induced to swell. A mechanism to explain the formation of this system of membrane tubules is proposed.

A freeze-fracture electron microscopic study of Frankia in root nodules of Alnus incana grown at three oxygen tensions

1990 ◽  
Vol 36 (2) ◽  
pp. 97-108 ◽  
Author(s):  
R. M. Abeysekera ◽  
William Newcomb ◽  
W. B. Silvester ◽  
John G. Torrey
Keyword(s):  
Root Nodules ◽  
Freeze Fracture ◽  
Alnus Incana ◽  
Electron Microscopic ◽  
Protection Mechanism ◽  
Transmission Electron ◽  
Actinorhizal Nodules ◽  
The Mean ◽  
Cell Envelopes ◽  
Fracture Electron

Nodulated plants of Alnus incana ssp. rugosa and ssp. incana were grown with the roots exposed to 5, 21, and 40 kPa O2. The nodules were studied by freeze-fracture transmission electron microscopy to determine the effect of varying O2 tension on the numbers of lipid laminae in the Frankia envelope. Lipid laminae were present in the cell envelopes of hyphae, stalks, and symbiotic vesicles. The mean number of lipid laminae in hyphal envelopes varied from five to nine. Stalks of symbiotic vesicles contained mean numbers of 35–59 lipid laminae over the range of pO2's studied. Symbiotic vesicle envelopes showed mean numbers of lipid laminae varying from 48 to 94. The numbers of lipid laminae were observed to increase significantly in the distal regions of the symbiotic vesicles in response to raised pO2 while the numbers on the proximal portions remained unchanged. The increase in the numbers of lipid laminae in response to raised pO2 was not sufficient to account for the expected increase in resistance to O2 required at the symbiotic vesicle envelope if lipid laminae formed the exclusive diffusion barrier to O2. These results suggest that lipid laminae surrounding symbiotic vesicles may not constitute the only O2 protection mechanism in Alnus nodules. Key words: Alnus incana, Frankia, nitrogen fixation, actinorhizal nodules, Actinomycetes.

Rhodopsin Particles in the Photoreceptor Membrane of an Insect

1976 ◽  
Vol 31 (11-12) ◽  
pp. 763-763 ◽  
Author(s):  
C. Bruce Boschek ◽  
Kurt Hamdorf
Keyword(s):  
Microscopic Examination ◽  
Visual Pigment ◽  
Particle Density ◽  
Substantial Reduction ◽  
Freeze Fracture ◽  
Electron Microscopic Examination ◽  
Electron Microscopic ◽  
Deficient Diet ◽  
Photoreceptor Membrane ◽  
Fracture Electron

Abstract Rhodopsin, Insect Photoreceptor, Freeze Fracture Electron-microscopic examination of freeze-fractured fly retinae has revealed the presence of particles, 80 to 100 Å in diameter, on the photoreceptor membrane. Flies which were raised on a vitamin-A deficient diet show a substantial reduction in the density of such particles. The reduction in particle density is in agreement with the reduction in visual-pigment concentration as measured spectrophotometrically for these flies. These results suggest that the particles are identical with molecules of the visual pigment, rhodopsin.

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