Biomembrane lipids

Martonosi, A. (1975) In Biomembranes - Lipids, Proteins and Receptors, Proc. of a NATO Advanced Study Institute (Burton. R.M. and Packer, L., Eds.), pp. 369-.390, Bi-Science Publications Div., Webster Groves, Missouri. 

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). 

DeKruijff B. Biomembranes - Lipids beyond the hilayer. Nature 1997 386 129-130. 

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. 

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. 

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