Membranes fluidity

Vesicle size, bilayer fluidity, membrane permeability, microviscosity, ability to bind small molecules, suseeptibility to pore formation, flip-flop rates, extent of water penetration, lateral amphiphile diffusion, vesiele fusion, and kinetic medium effeets (some of which will be discussed briefly below) all depend on the paeking of... 

Membrane effects. Drugs may alter synaptic transmission by affecting membrane organization and fluidity. Membrane fluidity is basically... 

Molecular Structures and Properties of Lipids Lipids in Biological Membranes Membrane Proteins Membrane Fluidity Membrane Asymmetry Erythrocyte Membrane... 

The primary site of action is postulated to be the Hpid matrix of cell membranes. The Hpid properties which are said to be altered vary from theory to theory and include enhancing membrane fluidity volume expansion melting of gel phases increasing membrane thickness, surface tension, and lateral surface pressure and encouraging the formation of polar dislocations (10,11). Most theories postulate that changes in the Hpids influence the activities of cmcial membrane proteins such as ion channels. The Hpid theories suffer from an important drawback at clinically used concentrations, the effects of inhalational anesthetics on Hpid bilayers are very small and essentially undetectable (6,12,13). 

Langmuir-Blodgett films (LB) and self assembled monolayers (SAM) deposited on metal surfaces have been studied by SERS spectroscopy in several investigations. For example, mono- and bilayers of phospholipids and cholesterol deposited on a rutile prism with a silver coating have been analyzed in contact with water. The study showed that in these models of biological membranes the second layer modified the fluidity of the first monolayer, and revealed the conformation of the polar head close to the silver [4.300]. 

Cells adjust the lipid composition of their membranes to maintain proper fluidity as environmental conditions change. 

Clofibrate causes a necrotizing myopathy, particularly in patients with renal failure, nephrotic syndrome or hypothyroidism. The myopathy is painful and myokymia of unknown origin is sometimes present. The mechanism of damage is not known, but p-chlorophenol is a major metabolite of clofibrate and p-chlorophe-nol is a particularly potent uncoupler of cellular oxidative phosphorylation and disrupts the fluidity of lipid membranes. Muscle damage is repaired rapidly on the cessation of treatment. 

A molecular variation of plasma membrane has been reported by Puccia et al. Reduction of total lipids (XL) content and significant variations of triglyceride (TG) and phospholipids (PL) fractions were observed as a consequence of exposure of C. intestinalis ovaries to TBTCl solutions. In particular, an evident TG decrease and a PL increase were observed, which probably provoked an increment in membrane fluidity, because of the high concentration of long chain fatty acids and, as a consequence, PL. This could be a cell-adaptive standing mechanism toward the pollutants, as observed in Saccharomyces cerevisiae. Also the increase in the content of the polyunsaturated fatty acids (PUPA), important in the synthesis of compounds such as prostaglandin which are present in the ovary in a stress situation, was probably a consequence of a defense mechanism to the stress provoked by the presence of TBTCl. 

Blasiak J. 1993. Parathion and methyl parathion-altered fluidity of native and model membranes. Pestic Biochem Physiol 45 72-80. 

Lopes VICF, Antunes-Madeira MC, Madeira VMC. 1997. Effects of methylparathion on membrane fluidity and its implications for the mechanisms of toxicity. Toxicol in Vitro 11 337-345. 

The fluidity of the cellular membrane presents a limiting factor at low temperatures. After a decrease in temperature, membranes are too rigid and must therefore be desaturated. Normally, membranes are in a liquid crystalline form... 

A shift in temperature from 38 to 22 °C leads to desaturation of fatty acids in Anabaena variabilis [110], resulting in control of the fluidity of the plasma membrane. Mutants have been isolated in Synechocystis PCC 6803 that were defective in desaturation of fatty acids, and the growth rate of one of these mutants was much lower than that of the wild-type at 22 °C [112]. It turned out that the mutant strain had a mutation in the gene desA, and when the wild-type allele was introduced into the chilling-sensitive cyanobacterium Anacystis nidulans, it resulted in increasing the tolerance of that strain to low temperature [113]. These experiments nicely demonstrate the existence of a mechanism of adaptation to low temperature in a chilling-tolerant cyanobacterium. 

This proves our theory that the membrane fluidity is an important parameter increasing shear stress resistance. The studies give two possibilities of improving the resistance lowering temperature or adding cholesterol. Which one is the most convenient is dependent on the cell line and the constraints of the process. 

In this context it is interesting to note that archaea, which possess S-layers as exclusive cell wall components outside the cytoplasmic membrane (Fig. 14), exist under extreme environmental conditions (e.g., high temperatures, hydrostatic pressure, and salt concentrations, low pH values). Thus, it is obvious one should study the effect of proteinaceous S-layer lattices on the fluidity, integrity, structure, and stability of lipid membranes. This section focuses on the generation and characterization of composite structures that mimic the supramolecular assembly of archaeal cell envelope structures composed of a cytoplasmic membrane and a closely associated S-layer. In this biomimetic structure, either a tetraether... 

The use of Upid bilayers as a relevant model of biological membranes has provided important information on the structure and function of cell membranes. To utilize the function of cell membrane components for practical applications, a stabilization of Upid bilayers is imperative, because free-standing bilayer lipid membranes (BLMs) typically survive for minutes to hours and are very sensitive to vibration and mechanical shocks [156,157]. The following concept introduces S-layer proteins as supporting structures for BLMs (Fig. 15c) with largely retained physical features (e.g., thickness of the bilayer, fluidity). Electrophysical and spectroscopical studies have been performed to assess the appUcation potential of S-layer-supported lipid membranes. The S-layer protein used in aU studies on planar BLMs was isolated fromB. coagulans E38/vl. 

The most common sterol in membranes is cholesterol (Chapter 14), which resides mainly in the plasma membranes of mammalian cells but can also be found in lesser quantities in mitochondria, Golgi complexes, and nuclear membranes. Cholesterol intercalates among the phospholipids of the membrane, with its hydroxyl group at the aqueous interface and the remainder of the molecule within the leaflet. Its effect on the fluidity of membranes is discussed subsequently. 

Figure 41-3. Diagrammatic representation of a phospholipid or other membrane lipid. The polar head group is hydrophilic, and the hydrocarbon tails are hydrophobic or lipophilic. The fatty acids in the tails are saturated (S) or unsaturated (U) the former are usually attached to carbon 1 of glycerol and the latter to carbon 2. Note the kink in the tail of the unsaturated fatty acid (U), which is important in conferring increased membrane fluidity.

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