Cell membrane, lipids

Ceiecoxib, NSAIDs and, 538 Cell membrane, lipid bilaver in,... 

Pyraflufen-ethyl is also used as the defoliant for cotton and as a desiccant for potatoes. Pyraflufen-ethyl is a novel inhibitor of protoporphyrinogen IX oxidase. Inhibition of this enzyme in chloroplasts causes accumulation of protoporphyrinogen IX, which results in peroxidation of foliar cell membrane lipids under the light and finally death of cells. 

Before the first indication of the existence of cannabinoid receptors, the prevailing theory on the mechanism of cannabinoid activity was that cannabinoids exert their effects by nonspecific interactions with cell membrane lipids (Makriyannis, 1990). Such interactions can increase the membrane fluidity, perturb the lipid bilayer and concomitantly alter the function of membrane-associated proteins (Loh, 1980). A plethora of experimental evidence suggests that cannabinoids interact with membrane lipids and modify the properties of membranes. However, the relevance of these phenomena to biological activities is still only, at best, correlative. An important conundrum associated with the membrane theories of cannabinoid activity is uncertainty over whether cannabinoids can achieve in vivo membrane concentrations comparable to the relatively high concentrations used in in vitro biophysical studies (Makriyannis, 1995). It may be possible that local high concentrations are attainable under certain physiological circumstances, and, if so, some of the cannabinoid activities may indeed be mediated through membrane perturbation. 

Several enveloped viruses, and some physical gene transfer techniques such as electroporation, deliver the nucleic acid into the cell by direct crossing of the cell membrane. Lipid-based, enveloped systems can do this by a physiological, selfsealing membrane fusion process, avoiding physical damage of the cell membrane. For cationic lipid-mediated delivery of siRNA, most material is taken up by endo-cytotic processes. Recently, direct transfer into the cytosol has been demonstrated to be the bioactive delivery principle for certain siRNA lipid formulations [151]. 

Amphipathic molecules can form bilayered lamellar structures spontaneously if they have an appropriate geometry. Most of the major cell membrane lipids have a polar head, most commonly a glycerophosphorylester moiety, and a hydrocarbon tail, usually consisting of two... 

A conceptualized cross section through a portion of the cell wall (rectangles), periplasmic space, and cell membrane (lipid bilayer with polar head groups in contact with cytoplasm and external medium, and hydrophobic hydrocarbon chains) of an aquatic microbe. Reactive functional groups (-SH, -COOH, -OH, -NH2) present on the wall consitutents and extracellular enzymes (depicted as shaded objects) attached by various means promote and catalyze chemical reactions extracellularly. 

Fittipaldi A, Ferrari A, Zoppe M, et al. Cell membrane lipid rafts mediate caveolar endocytosis of HIV-1 Tat fusion proteins. J Biol Chem 2003 278(36) 34141-34149. 

Furthermore, the effects of ozone on the cell membrane do not appear to be limited to ufa. Protein is also affected, particularly cell-membrane sulfhydryl groups and aromatic amino acids. Whether these protein effects are secondaiy to cell-membrane lipid peroxidation or arise as a direct result of ozone is not clear. 

Insulation. Lipids are excellent insulators. In the higher animals, neutral fats are found in the subcutaneous tissue and around various organs, where they serve as mechanical and thermal insulators. As the principal constituent of cell membranes, lipids also insulate cells from their environment mechanically and electrically. The impermeability of lipid membranes to ions allows the formation of the membrane potential (see p.l26). 

Targeting Biochemical Injuries to Cell Membrane Lipids... 

Ester synthesis of cholesterol linoleate. Cholesterol fatty acid ester is an important cell membrane lipids and has many applications in cosmetics, pharmaceutical and other industries. Akehoshi et aL(7) reported the ester synthesis of the cholesterol fatty acid ester with native lipase. Synthesis of the cholesterol fatty acid ester was also carried out in water-saturated n-hexane by palmitic acid-modified lipase. As shown in Table III, this system made it possible for the synthesis of the cholesterol fatty acid ester in organic solvents using the modified lipase. 

Cell membrane lipids are natural surfactants and display most of the properties of synthetic surfactants. The principal difference between these molecules and the surfactants that we discussed above in the chapter is that lipids contain two hydrocarbon tails per molecule. Table 8.5 shows the general structural formula of these cell membrane lipids and the names and formulas for some specific polar head substituents. The alkyl groups in these molecules are usually in the C 6-C24 size range and may be either saturated or unsaturated. 

Inhibition by altering integrity of cell membrane lipids... 

Cell membrane Lipid bilayer, containing surface proteins (peripheral proteins), proteins totally embedded in the membrane (intregal proteins), and glycoproteins partially embedded in the membrane Maintains ionic and chemical concentration gradients, cell-specific markers, intercellular communication, regulates cell growth and proliferation... 

Figure 3. Interaction of silica surface with a cell membrane lipid fragment at distances of 5-7A.

Solubilization of cell membrane lipids, for example the removal of cholesterol by surfactants such as bile... 

Hsiao LL, Howard RJ, Aikawa M, Taraschi TF. Modification of host cell membrane lipid composition by the intra-erythrocytic human malaria parasite Plasmodium falciparum. Biochem. J. 1991 274 121-132. 

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