Cell membranes, components

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. 

Hepatic steatosis usually is a result of excessive administration of carbohydrates and/or lipids, but deficiencies of carnitine, choline, and essential fatty acids also may contribute. Hepatic steatosis can be minimized or reversed by avoiding overfeeding, especially from dextrose and lipids.35,38 Carnitine is an important amine that transports long-chain triglycerides into the mitochondria for oxidation, but carnitine deficiency in adults is extremely rare and is mostly a problem in premature infants and patients receiving chronic dialysis. Choline is an essential amine required for synthesis of cell membrane components such as phospholipids. Although a true choline deficiency is rare, preliminary studies of choline supplementation to adult patients PN caused reversal of steatosis. 

It has been suggested [6] that these unusual sterols, especially in those cases where these unusual sterols comprise the entire sterol content of the organisms, likely replace conventional sterols as cell-membrane components. Evidence for this comes from subcellular fractionation and subsequent analysis of two marine sponges [10]. The sterol composition of the membrane isolates was found to be identical to that of the intact sponge. Most common variation of the marine sterol is in the side-chain, situated deep in the lipophylic environment of the phospholipid bilayer. This suggests that unusual fatty acids might accompany the sterols, and indeed this is often the case [8]. 

Be biocompatible (biomaterial) with the underlying epithelia by means of complete absence of cytotoxicity, ciliotoxicity, or other type of irreversible alterations of the cell membrane components ... 

The effect of soyasaponins on tumor cells may be mediated by mechanisms other than membrane permeability, because of their weak hemolytic activity. Saponins actively interact with cell membrane components, resulting in changes in intracellular morphology and cell membrane permeability. However, the differences between types of saponins and their effects on cell membrane are evident. 

Effects of Oxidative Stress on Neural Cell Membrane Components. 206... 

Phase I and II clinical trials indicated that acronycine reduced pain of the spine in some patients with multiple myeloma [280,282,283]. Acronycine has been reported to cause leukopoenia and to have CNS-depressant activity [284], Biochemically, acronycine inhibits incorporation of extracellular nucleosides into the RNA and DNA of leukaemia L-5178Y cell culture. There is, however, no evidence of interaction between acronycine and DNA or inhibition of template activity of DNA. This alkaloid does not inhibit nucleic acid synthesis in the cell, but rather inhibits the accumulation of extracellular uridine or thymidine, as nucleotides, in the intracellular precursor pool [285, 286], Acronycine, acting primarily on membranous organelles [287], seems to interfere with the structure, function and/or turnover of cell membrane components, thereby changing the fluidity of the plasma membrane [288]. 

We also prepared carbonate analogues by acylation of dihydro-QHS, consistent with Scheme 10. Although numerous analogues derived from DHQHS have appeared in the literature, linkage of DHQHS to cell-membrane components has not... 

Preissner KT. Anticoagulant potential of endothelial cell membrane components. Haemostasis 1988 18271-273. 

Lipids are naturally occurring organic molecules that have limited solub.ility in water and can be isolated from organi.sms by extraction with nonpolar organic solvents. 1-atS oils, waxes, many vitamins and hormones, and most nonprotein cell-membrane components are examples. Note that this definition differs from the sort used for carbohydrates and proteins in that lipids are defined by a physical property (solubility) rather than by structure. Of the many kinds of lipids, we ll be concerned in this chapter only with a few triacylglycerols, eicosanoids, terpenoids, and steroids. 

Cell membranes. Lipids, particularly the phospholipids, glycolipids, and cholesterol, are important cell membrane components throughout the body. Sphingomyelin, cerebrosides, and gangliosides are particularly important cell membrane constituents in the nervous system. 

Selection procedure. This is basically done by exposing the cell population to an antibody specific for an exposed cell membrane component (e.g. a specific protein, or an oligosaccharide determinant), and then adding complement to lyse all the cells that have bound enough antibody to trigger a cytotoxic effect. A selection procedure carried out on cells in suspension is described next. The same selection can also be applied to cell monolayers. 

The resulting affinity sensors can be composed of low-molecular weight biospecific ligands, proteins, enzymes, nucleic adds, and antibodies. Cell membrane components, cell organelles, and intact cells have also been employed. The latter approaches lead to immunosensors and receptrodes. 

The cholesterol that is used throughout the body is derived from two sources diet and de novo synthesis. When the diet provides sufficient cholesterol, the synthesis of this molecule is depressed. In normal individuals cholesterol delivered by LDL suppresses cholesterol synthesis. Cholesterol biosynthesis is stimulated when the diet is low in cholesterol. As described previously, cholesterol is used as a cell membrane component and in the synthesis of important metabolites. An important mechanism for disposing of cholesterol is conversion to bile acids. 

Halothane is believed to cause this severe hepatic damage via an immunological mechanism whereby antibodies to altered liver cell membrane components are generated by repeated exposure to a halothane-... 

Dietary lipid is absorbed in the small intestine and incorporated into chylomicrons which are secreted into the lymphatics and reach the bloodstream via the thoracic duct. In the circulation, triglyceride is gradually removed from these lipoproteins by the action of lipoprotein lipase. This enzyme is present in the capillaries of a number of tissues, predominantly adipose tissue and skeletal muscle. As it loses triglyceride, the chylomicron becomes smaller and detlated, with folds of redundant surface material. These remnants are removed by the liver. The cholesterol may be utilized by the liver to form cell membrane components or bile acids, or may be excreted in the bile. The liver provides the only route by which cholesterol leaves the body in significant amouiiLs. 

In certain organisms, e.g. the non-photosynthetic diatom Nitzschia alba, lecithine was found to be replaced by its sulphonium analogue (a phos-phatidyl-S,S-dimethylmercaptoethanol) as cell membrane component (Anderson et al., 1976) it was concluded that S-containing amino acids (e.g. cysteine, methionine) rather than serine probably act as primary precursors of the glycerophospholipids and sphingolipids which are involved in the formation of hydrophobic layers in membrane structures. 

DIRECTIONS Each of the numbered items or incomplete statements in this section is followed by answers or by completions of the statement. Select the ONE lettered answer or completion that is BEST in each case. 1. Chemical interactions between this drug and cell membrane components can result in the formation of pores lined by hydrophilic groups present in the drug molecule. 

Figure 7.7-2. Liposome-cell interactions. Drug-loaded liposomes can specifically (A) or nonspecificaiiy (B) adsorb onto the ceil surface. Liposomes can also fuse with the cell membrane (C) and release their contents into the cell cytoplasm, or they can be destabilized by certain cell membrane components when adsorbed on the surface (D) so that the released drug can enter the cell via micro-pinocytosis. Liposome can undergo the direct or transfer-protein mediated exchange of lipid components with the cell membrane (E) or be taken up by specific or nonspecific endocytosis (F). In the case of endocytosis, a liposome can be delivered by the endosome into the lysosome (G), or en route to the lysosome, the liposome can provoke endosome destabilization (H), which results in drug liberation into the cytoplasm. (With permission from Ref. 29.)...

Thus, saponins are apparently able to stimulate or suppress the immune system by two different mechanisms. In one mechanism, saponins interact with cell membrane components to alter cell permeability, membrane-associated enzymes, cell-surface receptors, and other components, and thus result in a nonspecific stimulation (or suppression) of phagocytosis, phagocytic chemiluminescence, and other functions of phagocytic lymphocytes. These effects can take place in vivo or in vitro. In the other mechanism, formation of imines (Schiff bases) by carbonyl-containing saponins can provide a co-stimulatory signal necessary for specific immunopotentiation of T cells that leads to a CMI response. This second mechanism, which is known as an adjuvant effect, takes place only in vivo, and is discussed in more detail in subsequent sections of this article. From previous work [62,73], it is expected that, for saponins with appropriate structures, both mechanisms would take place. Perhaps, the best-known case where both mechanisms can take place is that of the saponins derived from Q. saponaria Molina, which are next discussed in more detail. 

The work discussed here has shown that suspensions of platelets and red cells in a physiological medium can provide information for platelet surface interactions. Evidence is provided on the dynamic features of platelet-surface adhesion and detachment which indicates that more than one sequence of adhesion, detachment and re-adhesion can lead to the same net platelet adhesion. Surface generated substances, such as A DP and serotonin from platelets and thrombin from the coagulation pathway, may strongly influence the function of platelets approaching a surface. The supply of these substances depends on the presence of flow and continued arrival of platelets at a surface. The reactivity of surface-bound protein may be altered by platelet adhesion and detachment. This may occur as a result of deposition of cell membrane components, replacement of the original substrate with protein secreted from platelets or possibly by enzymatic digestion of surface bound protein. 

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