Membrane cycling

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... 

Lippincott-Schwartz J, Yuan LC, Bonitacino JS, et ol. (1989) Rapid redistribution of Golgi proteins into the ER in cells treated with brefeldin A Evidence for membrane cycling from the Golgi to the ER. In Cell 56 801 -813. 

Membrane Cycling in Secretion A Morphological Approach L. Orel... 

INEOS chlor offers both precious metal and nickel alloy coatings [192]. The precious metal coatings are deposited on a nickel substrate, and the electrocatalytically active layers are applied to the smface by thermal deposition or electroplating. Thermal spraying or vacuum deposition techniques form the nickel-alloy coating. These materials have been used in the FM 21 electrolyzers for over four membrane cycles. 

These membranes mimic natural photosynthesis except that the electrons are directed to form hydrogen. Several sensitizers and catalysts are needed to complete the cycle, but progress is being made. Various siagle-stage schemes, ia which hydrogen and oxygen are produced separately, have been studied, and the thermodynamic feasibiHty of the chemistry has been experimentally demonstrated. 

Fig. 18. Schematic representation of cycling of low density Hpoprotein (LDL) receptors from the plasma membrane to the cell interior.

Metallic Palladium films pass H9 readily, especially above 300°C. Ot for this separation is extremely high, and H9 produced by purification through certain Pd alloy membranes is uniquely pure. Pd alloys are used to overcome the ciystalline instability of pure Pd during heat-ing-coohng cycles. Economics limit this membrane to high-purity apphcations. 

Physical methods such as osmotic shock, in which the cells are exposed to high salt concentrations to generate an osmotic pressure difference across the membrane, can lead to cell-wall disruption. Similar disruption can be obtained by subjecting the cells to freeze/thaw cycles, or by pressuriziug the cells with an inert gas (e.g., nitrogen) followed by a rapid depressurization. These methods are not typically used for large-scale operations. 

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