Surface lipids

New developments in immobilization surfaces have lead to the use of SPR biosensors to monitor protein interactions with lipid surfaces and membrane-associated proteins. Commercially available (BIACORE) hydrophobic and lipophilic sensor surfaces have been designed to create stable membrane surfaces. It has been shown that the hydrophobic sensor surface can be used to form a lipid monolayer (Evans and MacKenzie, 1999). This monolayer surface can be used to monitor protein-lipid interactions. For example, a biosensor was used to examine binding of Src homology 2 domain to phosphoinositides within phospholipid bilayers (Surdo et al., 1999). In addition, a lipophilic sensor surface can be used to capture liposomes and form a lipid bilayer resembling a biological membrane. 

This broad class of hydrolases constitutes a special category of enzymes which bind to and conduct their catalytic functions at the interface between the aqueous solution and the surface of membranes, vesicles, or emulsions. In order to explain the kinetics of lipolysis, one must determine the rates and affinities that govern enzyme adsorption to the interface of insoluble lipid structures -. One must also account for the special properties of the lipid surface as well as for the ability of enzymes to scooC along the lipid surface. See specific enzyme Micelle Interfacial Catalysis... 

The PAL activity that is necessary for lignin formation occurs in the cytoplasm or bound to the cytoplasmic surface of the endoplasmic reticulum membranes. The cinnamic acid produced is probably carried on the lipid surface of the membranes, since it is lipophilic, and it is sequentially hydroxylated by the membrane-bound hydroxylases (47,50). In this way there is the possibility of at least a two-step channeling route from phenylalanine to p-coumaric acid. The transmethylases then direct the methyl groups to the meta positions. There is a difference between the transmethylases from angiosperms and those from gymnosperms, since with the latter... 

The transfer of bromine across liquid-liquid and gas-liquid interfaces is of considerable interest, for example, for sensor systems or for fundamental insights in the effects of bromine in the environment. A new methodology for kinetic studies at a lipid layer has been reported by Zhang etal. ]138]. A microelectrode immersed in the aqueous phase is placed in close distance to a lipid surface layer in contact with a gas phase. The oxidation of bromide at the electrode causes the formation of bromine, which in part escapes through the lipid layer into the gas phase (see Scheme 4). 

Figure 9. Electron micrograph of brain lipid surface film formed in presence of ATP alone, X 22,500...

Cellular anionic lipids have a twofold effect on DNA release from the lipo-plexes. They compensate the cationic lipid surface charge and eliminate the electrostatically driven DNA binding to the membrane interface, and they also disrupt the lipoplex structure and facilitate DNA departure into the solution by inducing formation of nonlamellar phases upon mixing with the lipoplex lipids. 

CHEMICAL SIMILARITIES BETWEEN MICROBUBBLE-SURFACTANT MONOLAYERS AND LIPID SURFACE FILMS AT THE AIR/SEA INTERFACE... 

G. Odham, B. Noren, B. Norkrans, A. Sodergren and H. Lofgren, Biological and chemical aspects of the aquatic lipid surface monolayer, Prog. Chem. Fats other Lipids 16 (1978) 31-44. 

Hydrated (e.g. protein and polysaccharide) surfaces adsorb ions less readily than hydrophobic (e.g. lipid) surfaces. 

Melittin, which is an amphipathic peptide from honeybee venom, consists of 26 amino acid residues and adopts different conformations from a random coil, to an a-helix, and to a self-assembled tetramer under certain aqueous environments see Fig. 9. We have carried out our systematic studies of the hydration dynamics in these three conformations using a single intrinsic tryptophan ( W19) as a molecular probe. The folded a-helix melittin was formed with lipid interactions to mimic physiological membrane-bound conditions. The self-assembled tetramer was prepared under high-salt concentration (NaCl = 2 M). The tryptophan emission of three structures under three different aqueous environments is 348.5 nm, 341 nm, and 333.5 nm, which represents different exposures of aqueous solution from complete in random-coil, to locating at the lipid surface of a nanochannel (50 A in diameter) in a-helix and to partially buried in tetramer. Figure 10 shows... 

Analysis of the results and comparison with the lipid phase transition observed iq the bulk lipid/water systems allows to conclude that the lowest temperature during heating at which measurable diffusion occurred correlates with the onset of formation of the lamellar Ln liquid crystalline phase of the given phospholipid. Therefore, the data support a correlation between the surface and bulk phase transitions. This was confirmed in recent studies where the lipid surface phase transition was successfully measured for the first time in foam film by independent means involving the detailed investigations of the temperature dependences of the W(C) curve for the foam film and its thickness. 

Before looking at the reconstituted membranes in more detail, we shall first discuss a simpler question concerning the distribution of ions in the aqueous phase of bilayer structures. Is the ion distribution in the water phase of typically 15 A width between the lipid surfaces homogenous, or is there a preferential binding to the polar head groups of the lipids These studies have been started in collaboration with G. Biildt and some preliminary results from dipalmitoyl phosphatidyl cholin (DPPC) membranes will be reported here. ... 

Considering techniques that allow the imaging of lipid surfaces, scanning probe microscopes such as the atomic force microscope (AFM) (13, 23) have become very appealing. The AFM allows measurements of native lipid samples under physiologic-like conditions and while biological processes are at work. It is hence often used to determine lipid membrane stmctures, stmctural defects in membranes, domain formation, and even the behavior of lipid rafts with high nanometer-scale lateral resolution. 

The term vitamin E refers to two groups of compounds, the tocophenols and the tocotrienols. The structures of these compounds appear in Figure 9.90. All forms of the vitamin contain two parts, a "head" and a "tail." The head consists of an aromatic ring structure, called chroman or chromanol, and is the site of antioxidant action. The tail of tocopherols is a phytyl group, while the tail of tocotrienols is a polyisoprenoid group. The tail of vitamin K setv es to anchor the vitamin in lipid membranes, in the lipids of adipose tissue, and in the lipid surface and core of the lipoproteins. 

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