Phospholipid bilayer systems

Milon, A., G. Wolff, G. Ourisson, and Y. Nakatani. 1986. Organization of carotenoid-phospholipid bilayer systems. Incorporation of zeaxanthin, astaxanthin, and their C50 homologues into dimyristoylphosphati-dylcholine vesicles. Helvet. Chim. Acta 69 12-24. 

This chapter summarizes the first direct determinations of conformational disorder in phospholipid bilayer systems. The model phospholipid chosen is 1,2 dipalmitoylphosphatidylcholine (DPPC), whose physical properties have been widely investigated for two... 

Fig. 6. r,/7-phase diagram for the main (chain-melting) transition of different phospholipid bilayer systems. The fluid (liquid-crystalline) L -phase is observed in the low-pressure, high-temperature region of the phase diagram. 

How does cholesterol leave the cell Since most cells do not secrete cholesterol esters (the known exceptions are hepatocytes and intestinal epithelial cells), free cholesterol must take its way to the outer bilayer of the cell membrane, where it may be removed by appropriate acceptors. It is likely that a net loss from the cell membrane involves movement of cholesterol from an area in the membrane with a high cholesterol-phospholipid ratio to an area with a lower ratio in the acceptor. The appropriate acceptors for cholesterol removal include any phospholipid bilayer system that contains little or no free cholesterol [125]. In vivo this is intact or nascent HDL [126,127]. Nascent HDL is a disc of phospholipid surrounded on its hydro-phobic perimeter by detergent-like apoproteins, such as the arginine-rich apoprotein and the HDL apoproteins, apo AI and apo All [128]. It is secreted from the liver and probably from the intestine (Chapter 5) into the plasma. Cholesterol enters nascent or intact HDL, and the lecithin-cholesterol acyltransferase (LCAT) reaction converts it to cholesterol ester [129,130] (Chapter 4). Since the ester is insoluble in the phospholipid bilayer it oils out into the centre of the particle. In this way. nascent discs are converted to spheres, and space for a new substrate, cholesterol, is created at the surface of the particle. Lipoproteins in lymph may also produce. similar effects on the cell surfaces exposed to this fluid. 

Milon A, Wolff G, Ourisson G and Nakatani Y (1986a) Organization of carotenoid-phospholipid bilayer systems. 

Influence of the Fatty Add Composition on the Phase Transition Temperature of Phospholipid Bilayer System... 

Chapter 7 is an interesting review by Kodama and Aoki (Japan) on the behavior of water in phospholipid bilayer systems. The authors distinguish between nonfreezable interlamellar water and freezable intralamellar and bulk water, and estimate the number of molecules of water in each category. They also examine the relationship between lipid phase transitions and ice-melting behavior in lipid-water systems. The behavior of water is also discussed in the gel phase of systems such as DPPC, DMPE, and DPPG. 

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