Lipid structural studies

When an analysis has been completed, the results can be expressed directly as weight percentages of the fatty acids for presentation in tabular form. On the other hand, it is often necessary to calculate the molar amounts of each acid as, for example, in most lipid structural studies (positional distributions and molecular species proportions). This is performed simply by multiplying the area of each peak by an arithmetic factor, obtained by dividing the weight of a selected standard ester (say 16 0) by the molecular weight of the component, followed by re-normalising to 100%. For convenience, these factors are also listed in Table 5.4. It should be noted that if fatty acid... 

A structural study on lipid A and the O-specific polysaccharide of the lipopoly-saccharide from a clinical isolate of Bacteroides vulgatus from a patient with Crohn s disease was conducted by Hashimoto and coworkers [39]. They separated two potent virulence factors, capsular polysaccharide (CPS) and lipopolysaccharide (LPS), from a clinical isolate of B. vulgatus and characterized the structure of CPS. Next, they elucidated the strucmres of O-antigen polysaccharide (OPS) and lipid A in the LPS. LPS was subjected to weak acid hydrolysis to produce the lipid A fraction and polysaccharide fraction. Lipid A was isolated by PLC, and its structure was determined by MS and NMR. 

The other anomalous behavior was the smaller-than-expected permeability of highly branched compounds. This deviation has been explained on the basis that membrane lipids are subject to a more highly constrained orientation (probably a parallel configuration of hydrocarbon chains of fatty acids) than are those in a bulk lipid solvent. As a result, branched compounds must disrupt this local lipid structure of the membrane and will encounter greater steric hindrance than will a straight-chain molecule. This effect with branched compounds is not adequately reflected in simple aqueous-lipid partitioning studies (i.e., in the K0/w value). 

Although El MS is an efficient way to provide structural information on several molecular constituents of various lipid substances it only provides partial information and it is particularly not suitable for the study of the low volatile components. High molecular weight and nonvolatile compounds are particularly difficult to analyse in this way and it may therefore be interesting to explore the possibilities of other ionisation modes such as electrospray for an accurate structural study of high molecular constituents such as monoester and diester species of beeswax (Gamier et al., 2002) and TAGs of animal fats... 

Here, we discuss a solid-state 19F-NMR approach that has been developed for structural studies of MAPs in lipid bilayers, and how this can be translated to measurements in native biomembranes. We review the essentials of the methodology and discuss key objectives in the practice of 19F-labelling of peptides. Furthermore, the preparation of macroscopically oriented biomembranes on solid supports is discussed in the context of other membrane models. Two native biomembrane systems are presented as examples human erythrocyte ghosts as representatives of eukaryotic cell membranes, and protoplasts from Micrococcus luteus as membranes... 

Afonin S (2004) Structural studies on membrane-active peptides in lipid bilayers by solid state 19F-NMR. PhD thesis, University of Jena... 

An important question arises about the effects of phospholipid composition and the function of membrane-bound enzymes. The phospholipid composition and cholesterol content in cell membranes of cultured cells can be modified, either by supplementing the medium with specific lipids or by incubation with different types of liposomes. Direct effects of phospholipid structure have been observed on the activity of the Ca2+-ATPase (due to changes in the phosphorylation and nucleotide binding domains) [37]. Evidence of a relationship between lipid structure and membrane functions also comes from studies with the insulin receptor [38]. Lipid alteration had no influence on insulin binding, but modified the kinetics of receptor autophosphorylation. 

S. Kawato, K. Kinosita, Jr., and A. Ikegami, Dynamic structure of lipid bilayers studied by nanosecond fluorescence techniques, Biochemistry 16, 2319-2324 (1977). 

Onodera s professor at that time was Dr. Bunsuke Suzuki, who later became a Professor of the University of Tokyo and was well known as a lipid investigator. Studies on the structure of fibroin, carbohydrate metabolism, separation of triglycerides from animals and plants, an analytic... 

The most fascinating characteristic some amphiphile molecules exhibit is that, when mixed with water, they form self-assembly structures. This was already discussed in Chapter 2 on micelle formation. Since most of the biological lipids also exhibit self-assembly structure formation, this subject has been given much attention in the literature (Birdi, 1999). Lipid monolayer studies thus provide a very useful method to obtain information about SAM formation, both concerning technical systems and cell bilayer structures. 

Film penetration studies show unequivocally that lecithin-cholesterol mixtures containing from 0 to 50 mole % cholesterol and lecithin—lactoside mixtures containing from 0 to 80 mole % Ci6-dihydroceramide lactoside have the same effect as pure lecithin. This suggests the presence of a lipid complex in which lecithin prevents the interaction of the cholesterol or ceramide lactoside with globulin. Over these ranges of composition the lipid film would consist of a mixture of the lecithin-cholesterol or the lecithin-lactoside complex with excess lecithin. One may picture two models in which the protein contact is restricted to molecules of lecithin. In one, individual polar groups of the protein interact with the excess lecithin molecules as well as with the lecithin portions of the complex. In the other model, the protein as a whole interacts with the lecithin sites of polymeric lipid structures. The latter, which could be referred to as surface micelles (I), are visualized also through the term "mono-... 

Structural studies of glycosphingolipids involves determination of the structure of the oligosaccharide chain and of the lipid moiety. For the oligosaccharide chain, it is necessary to determine the composition, molar ratio, and sequence of the monosaccharides, their pyranose or furanose nature, and the position of glycosidic bonds and their configuration for the lipid moiety, the composition of the fatty acids and sphingosine bases must be determined. Used for these purposes are the classical, chemical methods, conventionally accepted in the chemistry of carbohydrates and lipids and based on the degradation of compounds, enzymic, and physicochemical methods, primarily mass spectrometry and n.m.r. spectroscopy. 

Although the association between lipids and proteins is fundamental in understanding the physiological functions of membranes, information on such structures is very limited. Studies of a few systems of lipids and globular proteins indicate that the proteins tend to remain in their native form. The structures can be separated into two somewhat simplified types. Usually the lipid structure seems to dominate, and the protein molecules are incorporated into liquid crystalline structures of lipids. In other cases, the lipid molecules are distributed within the protein units,... 

The possibility of obtaining information about lipid-protein interaction makes Raman spectroscopy a useful technique for structural studies of membranes. As an illustration of spectra recorded from biological samples, see the Raman spectrum of a frog sciatic nerve in Figure 11. The C-H stretching vibration region is characteristic of lipid bilayers in a... 

Kleinschmidt JH, Tamm LK (2002) Structural transitions in short-chain lipid assemblies studied by P-31-NMR spectroscopy. Biophys J 83 994—1003... 

Ewert et al. present recent work on structural studies of cationic lipid/nucleic acid interaction, optimized for therapeutic nucleic acid delivery. Fundamental... 

Treatment with the surfactant is another way to break the barrier, as described earlier.10 The efficacy depends on each surfactant. Yang et al.15 suggested that some kinds of anionic surfactant, such as sodium dodecyl sulfate (SDS), affect not only the SC barrier, but also the nucleous layer of the epidermis. Fartasch demonstrated16 that the topical application of SDS caused cell damage to the nucleated cells of the epidermis and acetone treatment disrupted the lipid structure only in the SC. Thus, if one wants to investigate the effect of the disruption of the SC barrier function, tape stripping or acetone treatment would be better for the study. 

Pfeiffer, S. et al. High-pressure freezing provides new information on human epidermis simultaneous protein antigen and lamellar lipid structure preservation. Study on human epidermis by cryoimmobilization, J. Invest. Dermatol., 114, 1030, 2000... 

An improved understanding of the structure of the SC barrier is of interest for many reasons such as enhancing percutaneous penetration and, as discussed in this chapter, optimizing topical therapy for the treatment of dry or damaged skin. The results of this TEM work show that the lipid structure of the outer SC is quite variable. Typically, the intercellular spaces in the outer SC are considerably widened and filled with nonlamellar material. These data are consistent with earlier TEM studies13 14 and with an infrared spectroscopic study that found less structured lipids in the outer SC16 compared to the middle and inner regions. 

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