Intramembranous particles

Figure 2 shows FFEM images of Mal3 (Phyt)2/SQDG (9 1 mol/mol) vesicle membranes in the presence (Fig. 2A, B) or in the absence (Fig. 2C, D) of BR. Small particles were observed in Figure 2A, B, whereas no such particles were observed for pure Mai (Phyt)2/SQDG vesicles. In addition, two fracture faces of the bilayer membranes, a convex surface (a hydrophobic face of an inner leaflet, Fig. 2A) and a concave surface (a hydrophobic face of an outer leaflet, Fig. 2B) exhibited intramembraneous particles, suggesting BR was incorporated into vesicles transmembraneously.

Figure 9.15 Structures like reverse micelles in vivo. Membrane fusion intermediates (a) adhesion (b) joining (c) fission, (d) 1, Exocytotic fusion 2, semi-fused interbilayer connection 3, reverse micelles permitting enhanced permeability to Me +. (e) Aggregation of intramembranous particles in the sar-colemma after ischemia and reperfusion. (Modified from de Kruijff et al 1980, and from Cullis et al., 1986.)...

Conventional freeze-fracture replicas revealed the presence of the two membranes enveloping the hydrogenosomes presenting a different number and distribution of intramembranous particles (Fig. 7a-c) (Benchimol et al. 1996a Benchimol 2001). Four fracture faces were identified two concave faces representing the P faces of the outer and the inner membranes and two con-... 

Fig. 7 Freeze-fracture images of hydrogenosomes from T. foetus, a Fractured cell showing a prominent Golgi (G) with several lamellae and fenestrae, as well profiles of endoplasmic reticulum (ER) in close proximity (arrows) with hydrogenosomes (H). Bar = 100 nm. b Hydrogenosomes from an isolated fraction observed by freeze-fracture. Note the clusters of intramembranous particles forming rosettes (arrow). The peripheral vesicle is smooth and does not present clusters of particles or rosettes. Bar = 50 nm. (From Benchimol et al. 2001). c Two freeze-fractured hydrogenosomes exhibiting different fracture planes (arrows). Bar = 100 nm. (From Benchimol et al. 1996a)...

Israel M, Manaranche R, Morot Gaudry-Talarmain Y, Lesbats B, Gulik-Krzywicki T, Dedieu JC (1987) Effect of cetiedil on acetylcholine release and intramembrane particles in cholinergic synaptosomes. Biol Cell 61 59-63. 

MDR cell lines exhibit several other changes in surface membrane properties. Often, the structural order is increased in resistant cells as analyzed by electron spin resonance (ESR) and fluorescence anisotropy studies [98]. In addition, an increase in intramembranous particles and the rate of fluid-phase endocytosis are reported for resistant cells [99, 100]. 

Fig. 2.—A. A Model Depicting the Molecular Architecture of the Plasma Membrane of Oocystis apiculata During Secondary-wall Formation.74 [MF, Cellulosic microfibrils TC, terminal complexes PTC, paired, terminal complexes CR , regions of possible, transmembrane control GB, granule bands TCI, impressions of terminal, complex particles IP, intramembranous particles, AL, region of membrane phospholipids af-...

Hackenbrock CR, Hochh M, Chan RM. Calorimetric and freeze fractnre analysis of lipid phase transitions and lateral translational motion of intramembrane particles in mitochondrial membranes. Biochim. Biophys. Acta 1976 455 466 84. 

Suzuki, F. and Yanagimachi, R. (1989). Changes in the distribution of intramembraneous particles and filipin-reactive membrane sterols during in vitrol capacitation of golden hamster spermatozoa. Gamete Res. 23 335-347. 

The postsynaptic response to a chemical messenger appears to occur at postsynaptic active zones, which can be recognized morphologically at sites where nerve terminals make contact with other neurons or effector cells such as striated muscle. They consist of a pronounced density of intra-membranous particles as viewed under electron microscopy. These particles are at least 100-fold more enriched in active zones when compared to the remainder of the membrane. At the cholinergic nerve-muscle junction, evidence exists to suggest that these intramembranous particles are in fact ion channel—receptor complexes. Portions of the particles, thought to be the receptors, turn over with a time course of days, but the overall integrity of the active zones remains intact. In the cerebral cortex of the central nervous system, dendritic spines of neurons have been shown to be concentrated with active zones. These active zones appear to be intimately associated with portions of the neuronal cytoskeleton, since the cytoplasmic portion of the active zone displays a prominent band of fuzzy material, which, in turn, makes contact with microfilaments. 

Freeze-fracture studies indicate that mitochondrial cristae contain many protein-rich intramembrane particles. Some are the FqFi complexes that synthesize ATP others function in transporting electrons to O2 from NADH or other elec-... 

In schistosomes the tegument is about 4 /im thick. It is limited externally by a heptalaminate membrane that consists of two closely apposed lipid bilayers. Based on the distribution of intramembranous particles observed in freeze-fracture studies, the inner bilayer is the true plasma membrane of the parasite. The membrane extends inward 1-2 pm along numerous pits that branch and interconnect to form a lattice which increases the surface area of the parasite at least 10-fold (28). The tegument of... 

Vacuole membrane. The origin of the vacuole membrane is unclear. It is in continuity with the plasmalemma of the host cell through the moving junction during the invasion process, but its structure is dramatically different. It is almost completely devoid of intramembranous particles or host cell surface proteins. Contribution of host cell to the vacuole membrane is therefore probably restricted to lipids. 

Fig. 9. Freeze-fracture micrographs of the sarcolemma after ischemia and reperfusion showing severe >68 6gation of intramembranous particles (a) and the extrusion of multilamellar structures (b and c). A schematic representation of this lipid extrusion and IMP aggregation as a result of lateral phase segregation in the cytoplasmic leaflet is shown in d.

Fig. 15. Schematic representation of two immunogold techniques in combination with cryofracturing. A. Freeze-etch labelling in which labelled cells are fractured, etched, replicated and cleaned on acid. B. Label-fracture in which labelled cells are fractured, replicated and cleaned on water. Intramembranous particles (IMPs) are seen in projection with gold particles.

---