Lipid monolayers cholesterol effect

Since cholesterol is an important component of many biological membranes mixtures of polymerizable lipids with this sterol are of great interest. In mixed monolayers of natural lipids with cholesterol a pronounced condensation effect , i.e. a reduction of the mean area per molecule of phospholipid is observed68. This influence of cholesterol on diacetylenic lecithin (18, n = 12), however, is not very significant (Fig. 32). Photopolymerization indicates phase separation in this system. Apparently due to the large hydrophobic interactions between the long hydrocarbon chains of... 

The effect of the distance between the active center and the electrode on the reaction rate has been studied using as an example the electrocatalysis of the oxygen reduction reaction by laccase adsorbed on soot. Variation in the distance between the active center and the electroconductive substrate was achieved by inserting an intermediate monolayer of lipid molecules flatly and vertically oriented cholesterol molecules and vertically oriented lecithin molecules (scheme in Figure 36). In this case, the conditions of obtaining compact lipid monolayers were fulfilled. The subsequent setting of laccase did not lead to their desorption. 

Eeman M, Francius G, Dufrene YF, Nott K, Paquot M, Deleu M. Effect of cholesterol and fatty acids on the molecular interactions of fengycin with stratum comeum mimicking lipid monolayers. Langmuir 2009 25 3029-39. 

Malcharek S, Hinz A, Hilterhaus L, Galla H-J (2005) Multilayer Structures in Lipid Monolayer Films Containing Surfactant Protein C Effects of Cholesterol and POPE. Biophys J 88 2638-2649... 

Discontinuities are seen in the relationship between increase in film pressure, An, and lipid composition following the injection of globulin under monolayers of lecithin-dihydro-ceramide lactoside and lecithin-cholesterol mixtures. The breaks occur at 80 mole % C 16-dihydrocaramide lactoside and 50 mole % cholesterol. Between 0 and 80 mole % lactoside and between 0 and 50 mole % cholesterol the mixed films behave as pure lecithin. Two possible explanations are the formation of complexes, having molar ratios of lecithin-lactoside 1 to 4 and lecithin-cholesterol 1 to 1 and/or the effect of monolayer configurations (surface micelles). In this model, lecithin is at the periphery of the surface micelle and shields the other lipid from interaction with globulin. 

Although glycosphingolipids are the specific lipid components in the antigen-antibody complex, their activity is markedly enhanced by other (auxiliary) lipids such as lecithin and lecithin-cholesterol mixtures (15). The present study deals with the effect of lipid composition on the penetration of lactoside—cholesterol and lactoside—lecithin monolayers by rabbit y-globulin. We also investigated the lecithin-cholesterol system. Furthemore, since criteria for the existence of lipid-lipid complexes in monolayers are still few (8, 17), we have used infrared spectroscopy to examine lipid mixtures for the presence of complexes. 

Hopanoids (the most common organic natural product on earth) must have been involved in the evolution of the biomembrane itself. All known membranes contain terpene derivatives, such as cholesterol or carotenoids, which belong to, or can be derived from, hopanoids. However, we still do not know their biological function. Their most commonly proposed mechanism is to regulate membrane fluidity. Another obvious effect is their influence on the lipid bilayer (or monolayer in the case of archaebacteria) curvature. The different types of hopanoids occurring will certainly favour the relative stability of either the planar or of the intrinsically curved membrane conformation. The ether lipids of archaebacteria, which are hopanoid derivatives, forming curved bilayers as discussed above, therefore provide evidence for cubosomes as the first organised form of life. 

For simplicity of calculation, the core was assumed to contain all of the triglyceride and cholesteryl ester, although it is known that small amounts of the core lipids are dissolved in the surface monolayer, where they represent about 3 mol% of the surface lipids, and a larger fraction, about one ninth of the cholesterol, is dissolved in the core (Miller and Small, 1987). The presence of core lipids in the lipoprotein surface is very important metabolically, for the lipases and transfer proteins have access to these core lipids without having to penetrate the surface monolayer. For the calculation of composition, density, and size, however, the effects of component transfer between surface and core affect these quantities about one part in the fourth significant figure, and have been neglected in Table II. 

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