Membrane-associated particles

Koehler, J.K. and Gaddum-Rose, P. (1975). Media induced alterations of the membrane associated particles of the guinea pig sperm tail. J. Ultrastruct. Res. 57 106-118. 

Freeze-etch preparations of sterol-containing liposomes or erythrocyte membranes treated with amphotericin B did not reveal pits [256]. The postulated amphotericin B—sterol pores would be too small to be seen by this technique. However, freeze-etch studies of amphotericin B-treated plasma membranes isolated from Epidermophyton floccosum [261 ], a fungus pathogenic to man, has revealed depressions (or craters) and aggregates of membrane-associated particles (85 A in diameter). The areas of disruption did not traverse the membrane. 

The examination of the replicas from the two cases of ichthyosis vulgaris under study has led to the following observations The number of membrane associated particles and the appearance of the desmosomes are unchanged as compared to normal epidermis Gap junctions are absent in one case, while they are small and very rare in the other case In both cases, many tight junctions can be found in the spinous layer (Figure 11.1), which are seldom observed in normal epidermis Keratinosomes are quite numerous in the most... 

In the replicas, the unmodified number of membrane associated particles is no surprise, since this disease shows a normal mitotic index The usual arrangement of membrane associated particles in correspondence with the desmosomes substantiates thin section observations. On the contrary, the absence or the low number of gap junctions found is an Interesting fact. This phenomenon can possibly be ascribed to a vitamin A deficiency since, as is well known, this substance stimulates the synthesis of glycoproteins and RNA , binds to plasma proteins and has been experimentally shown to induce the formation of gap junctions . 

The ultrastructural features, visualized by freeze-fracture electron microscopy, of chloroplasts isolated from leaves of Arabidopsis mutants harvested at the rosette stage [18] have also been compared. A striking feature of the fracture faces of stacked thylakoids in the two mutants is the presence of aligned membrane-associated particles together with regions of randomly distributed particles. 

There is a substantial weight of evidence for the cytoskeleton being responsible for the force production and control of cell locomotion. This view has not yet been accepted unanimously. However, an alternative hypothesis continues to be argued which states that membrane cycling is the motive force driving cell locomotion (Bretscher, 1987). One of the predictions of the membrane flow hypothesis is that there should be a discernible flow of lipid from the front to the rear of the cell. Lipid flow has proven very difficult to study, because of the lack of suitable methods to label single lipid molecules and the heterogenous behavior of membrane-associated proteins. The observation that particles were transported rearward when they bound... 

Dyed particles also are commonly used in diagnostic lateral flow tests (like the common home pregnancy test), as the colors can be seen with the eye without the need for special detectors. In this type of assay, antibodies or antigens are coupled to the dyed particles and a sample solution applied to the test strip carries them along within a membrane. The particles then are captured at points in the membrane that represent either a control or a positive sample result. Large numbers of color particles docking at these points within the membrane create the visual lines associated with these disposable tests. 

The extent and specificity of the reactions of protein kinases and protein phosphatases are extremely dependent on the degree to which substrate and enzyme are localized at the same place in the cell. Many substrates of protein kinases occur either as membrane associated or particle associated forms (see 7.6.1, enzymes of glycogen metabolism). For protein kinases or protein phosphatases to perform their physiological function in a signal transduction process, they must be transported to the location of then-substrate in many cases (review Hubbard and Cohen, 1992 Mochly-Rosen, 1995). This is vahd both for the Ser/Tbr-specific protein kinases as well as for many Tyr-speci-fic protein kinases. In the course of activation of signal transduction pathways, com-partmentahzation of protein kinases, redistributed to new subcellular locations, is often observed. 

Not all hereditary traits follow the Mendelian patterns expected for chromosomal genes. Some are inherited directly from the maternal cell because their genes are carried in the cytoplasm rather than the nucleus. There are three known locations for cytoplasmic genes the mitochondria, the chloroplasts, and certain other membrane-associated sites.285 286 An example of the last is found in "killer" strains of yeast. Cells with the killer trait release a toxin that kills sensitive cells but are themselves immune. The genes are carried in double-stranded RNA rather than DNA, but are otherwise somewhat analogous to the colicin factors of enteric bacteria (Box 8-D). Similar particles (kfactors) are found in Paramecium.287... 

Both simple and complex species (e.g., water, lipids, proteins, lipoproteins, antibodies, enzymes, viruses, and small and large electrolyte ions) may be adsorbed on or transported across the interfaces of biological membranes, membrane subunits, and particles. These translocations are associated with membrane or particle formation, fusion, exchange, and lysis. The processes may be relevant to the movement, exchange, and clearance of extracellular material at the alveolar lining layer of the lung (7). Within this framework, the role of surface and hypophase viscosity has not been investigated. 

Tn view of the complicated microstructure of the muscle fiber one would - expect that formation of ice crystals within the very small cavities would cause some damage to various cellular elements. A point of particular interest is "What influence does freezing of muscle tissue have on the sensitive membranes associated with mitochondria, the sarcoplasmic reticulum, lysosomes, and other subcellular particles In order... 

While lipoproteins are the products of many different genes, the major apolipoproteins share properties distinguishing them from most lipid-free and membrane-associated proteins. For example, apolipoproteins consist of a single polypeptide chain that has relatively little tertiary structure. Most apolipoproteins contain stretches of amphipathic alpha-helix, whose hydrophobic face can be turned to the lipid surface of the particle. The apolipoproteins are flexible, as is reflected in their unusually small free energy of unfolding. As these apolipoproteins expand and contract at the cell surface, different protein domains are exposed that are detectable with monoclonal antibodies. These properties reflect the role of apolipoproteins at the surface of lipoprotein particles whose size changes as they circulate. 

The significance of the early membrane associated CL in monocytes is unknown, but appears to be specific, in that one of these unique peptides (f-Met-Phe) does cause CL and the other does not (f-Met-Ala). Support for specificity of this discriminatory response is provided by the data of Schiffman et al (1975), which point out that f-Met-Phe is more chemoattrac-tive for granulocytes than f-Met-Ala, This selectivity of response to dipeptides, the failure of zymosan to cause a burst of CL, and the dose response by latex particles, all suggest that early CL events are not spurious. On the other hand, their significance is currently only speculative. 

After 3 h of Ti02 (50 nm diameter) exposure, A549 cells internalised aggregates of the ultrafine particles which were observed in cytosolic, membrane-bound vacuoles (Stearns et al. 2001). After 24 h of exposure there were considerably more intracellular aggregates of membrane-bound particles, and aggregated particles were also enmeshed in loosely and tightly packed lamellar bodies. Throughout 24 h of exposure a preponderance of particles remained associated with the free surface of the cells and were not internalised. 

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