Lipid compositions, biomembranes

Gruner SM. Intrinsic curvature hypothesis for biomembrane lipid composition a role for nonbilayer lipids. Proc Natl Acad Sci USA 1985 82 3665-3669. 

The importance of lipid mesomorphic tendencies on cell membrane function has also been suggested by studies in which the lipid composition of cells has been varied. Such experiments are problematic because cells maintain regulatory apparatus that makes it difficult to alter the biomembrane lipid composition in a controlled manner. Furthermore, for eukaryotes, it is hard to obtain the pure membrane fractions of a single organelle membrane such as are required for meaningful determinations of the lipid compositions of particular membranes. In the case of bacteria, it is difficult to obtain pure plasma membrane fractions without cell wall contamination. However, my-coplasmas with only a single plasma membrane allow unambiguous determination of the overall plasma membrane composition. 

Abstract To understand how membrane-active peptides (MAPs) function in vivo, it is essential to obtain structural information about them in their membrane-bound state. Most biophysical approaches rely on the use of bilayers prepared from synthetic phospholipids, i.e. artificial model membranes. A particularly successful structural method is solid-state NMR, which makes use of macroscopically oriented lipid bilayers to study selectively isotope-labelled peptides. Native biomembranes, however, have a far more complex lipid composition and a significant non-lipidic content (protein and carbohydrate). Model membranes, therefore, are not really adequate to address questions concerning for example the selectivity of these membranolytic peptides against prokaryotic vs eukaryotic cells, their varying activities against different bacterial strains, or other related biological issues. 

Koynova R, MacDonald RC (2007) Natural lipid extracts and biomembrane-mimicking lipid compositions are disposed to form nonlamellar phases, and they release DNA from lipoplexes most efficiently. Biochim Biophys Acta-Biomembranes 1768 2373-2382... 

The influence of lipid phase (gel or liquid crystalline), cholesterol content, lipid composition (egg phosphatidylcholine or DPPC), and structure of benzodiazepines determine their localization in the membrane. The strength of benzodiazepine-membrane interaction increases with a decrease in molecular order, molecular packing, and hydration,. The authors point to the pharmacological relevance of theses results because the extent of partitioning of these drags into biomembranes would be coupled to local oscillation of membrane dynamics which may be induced by physiological events. ... 

Several classes of lipids common for the biomembranes can form inverted nonlamellar phases under physiologic conditions (4). The principle ones are phosphatidylethanolamines and monogalactosyldiglycerides. Also, cardiolipins and phos-phatidic acids can form inverted phases in the presence of divalent cations, and phosphatidylserines and phosphatidic acids both form inverted phases at low pH. Moreover, biomembrane lipid extracts and membrane-mimicking lipid compositions form nonlamellar phases if heated above physiologic temperatures, dehydrated, or treated with divalent cations (5-7). 

Natural biomembranes generally have a fluldllke consistency. In general, membrane fluidity is decreased by sphingolipids and cholesterol and Increased by phospho-glycerldes. The lipid composition of a membrane also influences its thickness and curvature (see Figure 5-8). 

As is evident from the work described up to this point, membranes may very well possess regions or domains differing in lipid composition and physical properties. The existence of heterogeneity in biomembranes could have great biological... 

Some final remarks concerning living membranes an important feature of biomembranes is the strongly heterogeneous lipid composition of the liquid crystal membrane matrix. Studies of mixed lipid monolayers demonstrate that the variation of the surface potential as a function of the area differs from that of pure monolayers depending on the composition, dAV/dA could either be enhanced or weakened. 

As known, cholesterol is one of the main structural elements of biomembranes. It is obtained that the DC content contributes in the inclusion of cholesterol in the lipid bilayer. It is seen from data, which is presented in the Fig. 3. However, the coefficient of the linear regression of the direct correlation between the cholesterol share in the total lipid composition and... 

Besides the inhibition of fatty acid biosynthesis the cyclohexane-1,3-dione derivates e.g. sethoxydim (Fig.3) also induce several other alterations of the plant composition and metabolism. Due to the herbicide-induced inhibition of fatty acid and biomembrane lipid formation, the development of functional chloroplasts, the formation of thylakoids and the chloroplast replication are also blocked (Lichtenthaler 1984, Lichtenthaler and Meier 1984) as well as the accumulation of chlorophylls and carotenoids (Lichtenthaler 1987, Lichtenthaler et al. 1987) but not their biosynthesis (Lichtenthaler 1987). This resulted in the formation of white leaf parts which are free of photosynthetic pigments. Furthermore, in herbicide-treated maize shoots the accumulation and biosynthesis of plastidic and cytoplasmic phospho- and glykolipids was blocked (Burgstahler and Lichtenthaler 1984 and Burgstahler 1985). The cyclohexane-1,3-dione derivatives block the... 

Among the diverse components of biomembranes, lipids are essential in structural aspects. Lipids are defined operationally as derivatives of fatty acids and their metabolites. As lipids are usually amphiphilic molecules with hydrophobic hydrocarbon tails and hydrophilic head groups (as shown in Figure 1), the bilayer structures of biomembranes are held with hydrophobic forces to the tails and heads of lipids. Another major component of biomembranes is proteins. The weight proportion of proteins in biomembranes is often more than that of lipids. As proteins are more rigid than lipid assemblies, specific interactions by biomembranes are often related to proteins. Further, the sterols contained in biomembranes play unique roles in their apolar regions. As the functionality of biomembranes arises from the diversity of their composition, various kinds of molecules have been studied for biomembrane modeling. 

Although the drug delivery to the lipid bilayer membrane is just the first step for bioactivities and phopholipid vesicles are rather simple in view of the composite structure of biomembranes, the unambiguous specification of the preferential location of the drug is essential the successive processes of the action are expected to be induced via the delivery site in membranes. We expect more advances in the dynamic NMR study, so that we can get insight into the mechanism of DD in membranes. 

Given the overwhelming compositional complexity of biomembranes, a slightly better representation can be achieved when lipid extracts from native sources are used... 

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