Cholesterol interactions

Ohvo-Rekila, H., Ramstedt, B., Leppimaki, P. and Slotte, J. P. (2002). Cholesterol interactions with phospholipids in membranes, Progr. Lipid Res., 41, 66-97. 

Cholesterol interacts with glacial acetic acid and acetic anhydride to result into the formation of a coloured product whose absorption is measured at 630 nm and this is found to be directly proportional to the level of cholesterol present in the serum. The reaction may be expressed as follows ... 

The unsaturated phospholipid from soybean lecithin also shows a similar effect, while the unsaturated phospholipids from red blood cell membranes, although showing a slight effect of cholesterol interaction, still show a prominent polymethylene peak in the high resolution spectrum. 

When the membrane is washed with ether to remove all of the cholesterol, the resultant PMR spectrum shows little change in the intensity of the polymethylene chain signal compared with that of the original membrane spectrum. This appears to rule out lipid-cholesterol interaction in this membrane as having a dominant effect upon the polymethylene chain freedom. In the membrane fragments either lipid chain-chain interactions have increased as a result of the protein interaction... 

Zheng L, McQuaw C, Ewing A, Winograd N (2007) Sphingomyelin/phosphatidylcholine and cholesterol interactions studied by imaging mass spectrometry. J Am Chem Soc 129(51) 15730-15731. doi 10.1021/ja0741675... 

The effects of cholesterol and cholesterol-derived oxysterols on adipocyte ghost membrane fluidity has been studied. It has been found that cholesterol and oxysterols interact differently with rat adipocyte membranes. Cholesterol interacts more with phosphatidylcholine located at the outer lipid bilayer whereas, for example, cholestanone seems to interact more with phospholipids located at the inner layer... 

In another study, the in vitro modulation of rat adipocyte ghost membrane fluidity by cholesterol oxysterols was investigated [55]. It was found that cholesterol oxy-sterols interact differently with rat adipocyte membranes. Cholestanone interacts predominantly with the phospholipids located at the inner leaflet (e.g. PE), whereas cholesterol interacts preferably with the phospholipids (PC) of the outer layer. 

Among their diverse biological activities, saponins possess effective hypocholesterolemic action (Price et al., 1992). Saponin-cholesterol interaction is an important part of the hypocholesterolemic action of alfalfa but interactions of bile acids with other components of alfalfa might be equally important. Alfalfa plant and sprout saponin have been found to be effective in binding significant amounts of cholesterol (Wang and Ng, 1999). 

Permeabilizes membranes e.g. mitochondrial digitonin particles cholesterol interaction [antifungal, detergent, haemolytic]... 

Vibrational spectroscopy shows that inclusion of cholesterol in phospholipid bilayers tends to decrease the fluidity of the hydrophobic region above the main transition point Tm and to increase it below Tm. The presence of cholesterol in DPPC or DMPC muti-layered vesicles does not affect the transition point but simply broadens the transition by decreasing the CH2-stretching wavenumber in the liquid crystalline phase and by increasing it in the gel-like phase (Lippert and Peticolas, 1971 Spiker and Levin, 1976 Casal and Mantsch, 1984). There is also evidence that lipid-cholesterol interaction increases the amount of bound water in the headgroups (Levin et al., 1985). 

Terova B, Heczko R, Slotte IP. On the importance of the 54. phosphocholine methyl groups for sphingomyelin/ cholesterol interactions in membranes a study with ceramide phospho-ethanolamine. Biophys. J. 2005 88 2661-2669. 

Although some membrane proteins are known to interact with cholesterol, cholesterol interactions with other lipids have been studied much more thoroughly. Most notably, cholesterol interacts strongly with sphingomyelin, perhaps by forming complexes, which results in a liquid-liquid phase separation of cholesterol-rich and cholesterol-poor phases (13). The cholesterol-rich phases exhibit more chain order and therefore are referred to as liquid-ordered (lo) phases, whereas the cholesterol-poor phases are called liquid-disordered (Id) phases. 

Steroidogenesis synthesis of steroid hormones from cholesterol. Interactions of Fat Metabolism Pathways ... 

Cholesterol interacts with proteins and influences their function. 

Wang EJ, Casciano CN, Clement RP, Johnson WW. 2000. Cholesterol interaction with the daunorubicin binding site of P-glycoprotein. Biochem. Biophys. Res. Commun. 276(3) 909-16... 

A question of some importance is whether cholesterol in biomembranes can affect the function of membrane proteins. Several systems have now been examined and a number of conflicting ideas have been put forward. Let us first consider what is known about intrinsic protein-cholesterol interactions. 

H. L. Scott, Biophys.]., 59,445 (1991). Lipid-Cholesterol Interactions (Monte Carlo Simulations and Theory). 

Ohvo-Rekila H, Ramstedt B, Leppimaki P, Slotte JP. Cholesterol interactions with phospho-hpids in membranes. Prog Lipid Res 41(2002) 66-97. 

Biological membranes contain large numbers of insertions, e.g., embedded proteins and cholesterols. Interaction between insertions includes direct forces, such as electrostatic and van der Waals, and also interactions mediated by the membrane. Our focus here is on the interactions caused by the insertion-induced elastic deformations in membranes. 

M. J. Blandamer, B. Briggs, P. M. CuUis, B. J. Rawlings, J. B. F. N. Engberts, Vesicle-cholesterol interactions effects of added cholesterol on gel-to-liquid crystal transitions in a phosphohpid membrane and five dialkyl-based vesicles as monitored using DSC, Phys. Chem. Chem. Phys., 2003, 5, 5309-5312. 

It is a well-known experimental fact that incorporation of cholesterol in lipid bilayers affects the mechanical and transport properties of membranes. This includes their increased bending elasticity (22) and reduced passive permeability to small molecules (23, 24). Despite a great deal of theoretical and experimental research, no definitive microscopic understanding of phospholipid-cholesterol interactions has been proposed yet. 

The stoichiometry of the polyene antibiotic—cholesterol interaction has been measured in various systems with different techniques. The filipin—cholesterol interaction has been the subject of extensive study and the results suggest this interaction is equimolar. The data on other polyenes is not so definite, but suggests that only a small number of sterol molecules interact with one polyene antibiotic molecule. 

Fluorometric and spectrophotometric studies of filipin-cholesterol interaction showed that the stoichiometry of the interaction was 1 1 [150] or 1 1.5 [146,147]. UV spectrophotometry changes have been used to monitor the stoichiometry of the interaction between filipin and free or liposome-bound cholesterol. Analysis of aqueous dispersions suggested that the stoichiometry was 1 1 [171]. Lecithin, dicetyl phosphate-cholesterol liposomes only produced maximal spectral changes of filipin when the sterol polyene ratio was 1 1 [172]. Filipin released trapped ion markers from sterol—phospholipid liposomes. The rate of release was dependent upon cholesterol content of the liposome membrane (maximum at sterol phospholipid ratio of 1 1) and upon the molar fllipin sterol ratio (maximum at fllipin sterol ratio of 1 1). 

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