Supported membranes concepts

Supported membrane concepts that were studied in the past 10 years include 5-p.m-thick dense Pd on supported y-alumina (Pacheco Tanaka et al., 2006), 10-p m-thick dense Lao.sSro.sCoOa.g for O2 purification (van der Haar, 2001), 60-nm thin amorphous silica for small gas molecule separation and water pervaporation (de Vos and Vetweij, 1998), >1 xm-thick MFI zeolite membranes for parajortho-xyicnc isomer separation (Caro et al., 2000), 0.4-2-p.m thick mesoporous y-alumina (Yu et al., 2006), and 4 p,m mesoporous C0AI2O4 for nanofiltration of liquids (Condom et al., 2006). 

The mixing of nematogenic compounds with chiral solutes has been shown to lead to cholesteric phases without any chemical interactions.147 Milhaud and Michels describe the interactions of multilamellar vesicles formed from dilauryl-phosphotidylcholine (DLPC) with chiral polyene antibiotics amphotericin B (amB) and nystatin (Ny).148 Even at low concentrations of antibiotic (molar ratio of DLPC to antibiotic >130) twisted ribbons are seen to form just as the CD signals start to strengthen. The results support the concept that chiral solutes can induce chiral order in these lyotropic liquid crystalline systems and are consistent with the observations for thermotropic liquid crystal systems. Clearly the lipid membrane can be chirally influenced by the addition of appropriate solutes. 

Because the mucus layer or the underlying cells may serve as either final accumulation sites of toxic gases or layers through which the gases diffuse en route to the blood, we need simplified models of these layers. Altshuler et al. have developed for these layers the only available model that can be used in a comprehensive system for calculating tissue doses of inhaled irritants. It assumes that the basement membrane of the tracheobronchial region is covered with three discrete layers an inner layer of variable thickness that contains the basal, goblet, and ciliated cells a 7-Mm middle layer composed of waterlike or serous fluid and a 7-Mm outer layer of viscous mucus. Recent work by E. S. Boatman and D. Luchtel (personal communication) in rabbits supports the concept of a continuous fluid layer however, airways smaller than 1 mm in diameter do not show separate mucus and serous-fluid layers. 

Comparson of the transitions observed by differential scanning calorimetry in membranes of M. laidlawii and in water dispersions of the lipids from the membranes support the concept that most of the lipids exist as a smectic mesophase in the membranes. The evidence for a bilayer structure is straightforward in this case. Lipid transition temperatures are a function of fatty acid composition and correlate well with biological properties. The calorimeter possesses advantages over high resolution NMR for M. laidlawii, and perhaps in many other systems, because the data can be interpreted less ambiguously. In M. laidlawii membranes the bilayer appears to be compatible with the same physical properties observed in other membranes—a red-shifted ORD, lack of ft structure in the infrared, reversible dissociation by detergents, and poorly... 

The uptake and accumulation of various amino acids in Lactobacillus arabinosus have been described. Deficiencies of vitamin B6, biotin, and pantothenic acid markedly alter the operation of these transport systems. Accumulation capacity is decreased most severely by a vitamin B6 deficiency. This effect appears to arise indirectly from the synthesis of abnormal cell wall which renders the transport systems unusually sensitive to osmotic factors. Kinetic and osmotic experiments also exclude biotin and pantothenate from direct catalytic involvement in the transport process. Like vitamin B6, they affect uptake indirectly, probably through the metabolism of a structural cell component. The evidence presented supports a concept of pool formation in which free amino acids accumulate in the cell through the intervention of membrane-localized transport catalysts. 

FIGURE 6.10 Different membrane concepts for oxygen-ion conducting membranes, (a) Dense mixed conducting membrane top-layer supported on an asymmetric macroporous support (b) dense self-supported mixed conducting membrane with graded porous interfaces and (c) solid electrolyte cell (oxygen pump). 

A study by LeBlond and Marcel (1991) using monoclonal antibodies supports the concept of a biological role for the direct interaction of amphipathic helices with plasma membranes these authors suggest that the optimum uptake of. . . HDL. . . requires the. . . cooperative binding of the amphipathic a helical repeats [of apoA-I] to HepG2 cell membranes. Consistent with direct interaction of amphipathic helixes with plasma membranes is the fact that apoA-I, apoA-II, and apoA-lV bind equally well, even though apoA-11 is made up almost entirely of class A amphipathic helical domains (Fig. 7). 

Kusakabe et al.83 proposed selective CO oxidation membrane concept to facilitate SMR reaction. Yttria-stabilized zirconia (YSZ) membrane was deposited on the surface of a porous alumina support tube by sol-gel procedure. This again was impregnated with Pt and Rh aqueous solution to produce a Pt- or Rh-loaded YSZ membrane. With addition of 02 in the feed, oxidation of CO can bring CO concentration to the level appropriate for PEMFC (<30ppm). 

Balchum et al. (1971) have provided evidence supporting the concept that the peroxidation or ozonization of unsaturated fatty acids in biological membranes is a primary mechanism of the deleterious effects of 03. The hypothesis is based on the tendency of 03 to react with the ethylene groups of unsaturated fatty acids, resulting in the formation of free radicals. The free radicals can, in the presence of molecular oxygen, cause peroxidation of unsaturated fatty acids. In support of this hypothesis is the evidence that after 03 exposure there was a relative decrease in unsaturated fatty acids as compared to saturated fatty acids, and the more unsaturated the fatty acid, the greater the loss. Furthermore, a deficiency of vitamin E increases the toxicity of 03 for the rat (Goldstein et al. 1970). 

Fig. 10.1. Different membrane concepts incorporating an oxygen ion conductor (a) mixed conducting oxide, (b) solid electrolyte cell (oxygen pump), and (c) dual-phase membrane. Also shown is the schematics of an asymmetric porous membrane (d), consisting of a support, an intermediate and a barrier layer having a graded porosity across the membrane.

The immediate segregation of proteins in the ER suggested that translocation across the membrane may be coupled to translation. The experiments of Redman and Sabatini (1966) supported this concept on a molecular level. After addition of puromycin, an inhibitor of protein elongation, to growing cells, N-terminal fragments of secretory proteins were found in the lumen of the ER, and not in the cytoplasm. In later work, Sabatini and Blobel (1970) showed that inclusion of microsomes of RER in a cell-free system translating mRNA coding for secretory pro-... 

These observations are consistent with the mosaic model of the membrane that was derived from monolayer studies (2, 4, 5, 12, 13). Therein, the structural or bimodal (amphipathic) protein in the membrane (natural or artificial) interacts with the polar peripheries of the polymeric lipid structures alongside the protein. The EPR data of Jost et al. (29) support this concept, i.e., an appreciable portion of the lipid is in lateral hydrophilic bonding with the protein whereas the other lipid is free, probably within the lipid cluster, and preserves the lipid character. 

Calmodulin has been reported to stimulate membrane-bound adenylate cyclase in the presence of Ca ". Some reports suggest that Ca " " is required for the stimulation of dopamine-dependent adenylate cyclase and that the sensitivity of adenylate cyclase to a neurotransmitter is regulated by the presence of membrane-bound calmodulin, which binds the Ca required for dopamine stimulation of the enzyme. Furthermore, these reports present data that support the concept that cAMP-dependent phosphorylation of the plasma membrane leads to a release of membrane-bound calmodulin, thereby providing a feedback loop for the control of adenylate cyclase activity. The appearance of calmodulin in soluble fractions of the cell would also result in the activation of phosphodiesterase, which would further attenuate cAMP activity. 

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