Phospholipids monolayer-forming

Using the phospholipid DMPC, it was formed a planar supported adlayer structures by vesicle fusion. Lipid bilayer formation proceeds on a hydro-xythiol-terminated Au surface. Phospholipid monolayers form on hydro-xythiol-terminated gold surfaces that have been treated with aqueous POCI3 and ZrOCl2 prior to lipid deposition, providing an interface that interacts... 

The effect is more than just a matter of pH. As shown in Fig. XV-14, phospholipid monolayers can be expanded at low pH values by the presence of phosphotungstate ions [123], which disrupt the stmctival order in the lipid film [124]. Uranyl ions, by contrast, contract the low-pH expanded phase presumably because of a type of counterion condensation [123]. These effects caution against using these ions as stains in electron microscopy. Clearly the nature of the counterion is very important. It is dramatically so with fatty acids that form an insoluble salt with the ion here quite low concentrations (10 M) of divalent ions lead to the formation of the metal salt unless the pH is quite low. Such films are much more condensed than the fatty-acid monolayers themselves [125-127]. 

The popular applications of the adsorption potential measurements are those dealing with the surface potential changes at the water/air and water/hydrocarbon interface when a monolayer film is formed by an adsorbed substance. " " " Phospholipid monolayers, for instance, formed at such interfaces have been extensively used to study the surface properties of the monolayers. These are expected to represent, to some extent, the surface properties of bilayers and biological as well as various artificial membranes. An interest in a number of applications of ordered thin organic films (e.g., Langmuir and Blodgett layers) dominated research on the insoluble monolayer during the past decade. 

Koryta et al. [48] first stressed the relevance of adsorbed phospholipid monolayers at the ITIES for clarification of biological membrane phenomena. Girault and Schiffrin [49] first attempted to characterize quantitatively the monolayers of phosphatidylcholine and phos-phatidylethanolamine at the ideally polarized water-1,2-dichloroethane interface with electrocapillary measurements. The results obtained indicate the importance of the surface pH in the ionization of the amino group of phosphatidylethanolamine. Kakiuchi et al. [50] used the video-image method to study the conditions for obtaining electrocapillary curves of the dilauroylphosphatidylcholine monolayer formed on the ideally polarized water-nitrobenzene interface. This phospholipid was found to lower markedly the surface tension by forming a stable monolayer when the interface was polarized so that the aqueous phase had a negative potential with respect to the nitrobenzene phase [50,51] (cf. Fig. 5). 

Example 13.3 demonstrates that phospholipids can form domains of distinct two-dimensional shapes on liquid surfaces. It has been found that the domain shape mainly depends on the chemical composition of the monolayer and the conditions such as temperature, pH, and ionic concentration. Domain structures can usually be understood by taking two competing interactions into account an attractive dispersive van der Waals force and a repulsive dipole-dipole... 

LB monolayers and Y-type bilayers lead us to bilayers, hemimicelles, and micelles (Fig. 4.12). A bilayer of phospholipid amphiphiles forms the cell wall, which surrounds each living cell (prokaryotic and eukaryotic) the ionic outer layers contact the bulk solution (blood, serum, etc.), while the... 

A question of interest here is the origin of the DMPC molecules building up the bilayer, considering the low monomer concentration in the DMPC suspension and the small volume of the drop in the cell. However, as indicated in Section 3.4.3, NBF can be formed only at close packing at the interface (r ). A possible mechanism is the vesicle degradation at the surfaces, i.e. at the solution/air interface. An evidence of this mechanism are the kinetic studies of insoluble phospholipid monolayer of Ivanova et al. [291]. Nevertheless, NBF formation from vesicle suspensions needs further research. 

In addition to fatty acids and phospholipids, steroids form another elass of surfactants that are often subjected to monolayer studies. As an example a /r(aj)-isotherm for cholesterol is shown in fig. 3.13. Up to a molecular area of 0.50 nm the spread molecules hardly interact with each other. The limiting area in the condensed phase is ca. 0.40 nm per molecule, which is compatible with an orientation of the cholesterol molecules in the monolayer as indicated in the inset. It is historically interesting that establishing this cross-section has contributed to solving the structure of sterols. 

IR spectroscopy of the X-receptor protein signal peptide in phospholipid monolayers shows that the peptide affects the packing of the lipid hydrocarbon tails (M. S. Briggs, R. A. Dluhy, D. G. Cornell, and L. M. Gierasch, unpublished results). In samples formed at the same surface pressure, the lipid tails are oriented differendy in the presence and absence of signal peptide. A phospholipase assay for structural defects in phospholipid bilayers (Jain et al., 1984) indicates that the X-receptor protein signal peptide interacts with vesicles to induce such defects. The peptides perturb the lipid structure at lower mole fractions than do various lysophospholipids. These data provide yet another indication that signal peptides interact with and perturb lipid complexes. 

Fig. 10. IR spectra of the wild-type E. coli LamB synthetic signal peptide in phospholipid monolayers. (A) Peptide adsorbed to the monolayer (film formed above the critical insertion pressure of the peptide). (B) Peptide adsorbed and inserted (film formed below the critical insertion pressure). Characteristic amide I bands for a-helix (or random coil) 1660 era", for -structure 1630 era. The amide III band (at lower frequencies) was used to confirm that the 1660 cm band was due to helix and not coil. Experimental details are reported in Briggs et al. (1986). Copyright 1986 by the American Association for the Advancement of Science.

A phospholipid monolayer in the surface is consistent with the current model that LD are formed by TAG deposition between the two leaflets of the ER membrane and may remain connected to it [144, 145 see below]. Distribution of acyl-CoA cholesterol acyltransferase-1, a major enzyme that synthesizes cholesterylester, in the entire ER [148] seems to indicate that LD may bud anywhere along the membrane. However, Cap-LC/ESI mass spectrometry showed that FA moieties of phosphatidylcholine and lyso-phosphatidylchohne in LD are distinct from those in the rough ER [149]. The results do rule out the generation of the LD surface generated from the ER membrane but indicate that the former is a highly differentiated domain. Mature LD might be independent of the ER. Alternatively, the LD may be connected to the ER, but some molecular mechanism may demarcate the LD surface from the bulk ER membrane as postulated for other ER domains [150]. Whatever is true, TAG synthesized in wide areas of the ER do not deposit indiscriminately but are concentrated to loci specialized to make LD. ADRP or other LD-associated proteins may be involved (see below). 

As already noted, when the LE phase is expanded, bubbles of gas grow and thin lamellae of fluid are left between them, forming a two-dimensional foam structure (Fig. 10a) in which the size of the cells and the distribution of the number of sides changes with time. Dendritic structures (Fig. 21) are observed in the LE-LC transition region when the monolayer is compressed, or in temperature quenches from the LE one-phase region into the two-phase region. In the case of fatty acids,only circular islands are observed at low temperature, even with rapid compression. The temperature threshold for the appearance of dendritic patterns is quite sharp. Such structures are also found in phospholipid monolayers. ... 

In this assay (Demel et al., 1977 Demel et al., 1982), a monolayer, containing 14C-labeled phospholipid, is formed at an air—water interface. Vesicles and exchange protein are injected into the subphase. The loss of radioactivity from the surface is monitored continuously with a gas flow detector. Alternatively, the rate of transfer of radiolabeled lipids is measured by recovering the subphase or monolayer and quantitating the radiolabeled lipids. The difficulty in preparing the monolayers and the... 

A FIGURE 5-7 Gel and fluid forms of the phospholipid bilayer. (Top) Depiction of gel-to-fluid transition. Phospholipids with long saturated fatty acyl chains tend to assemble into a highly ordered, gel-like bilayer in which there is little overlap of the nonpolar tails in the two leaflets. Heat disorders the nonpolar tails and induces a transition from a gel to a fluid within a temperature range of only a few degrees. As the chains become disordered, the bilayer also decreases in thickness. Bottom) Molecular models of phospholipid monolayers in gel and fluid states, as determined by molecular dynamics calculations. 

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