HYDRATION OF PHOSPHOLIPID-BILAYERS IN THE PRESENCE AND ABSENCE OF CHOLESTEROL

Differential scanning calorimetry (DSC) was used for determining the n umber of unfreezable water molecules per molecule of phosphatidylserin e from bovine spinal cord (PS) or dimyristoyl phosphatidylserine (DMPS ) and dimyristoyl phosphatidylcholine (DMPC), alone or in mixtures wit h cholesterol. It was assumed that the unfreezable water molecules are tightly bound to the phospholipid. It was found that when the phospho lipids are in the gel state and in the absence of cholesterol, PS bind s 2.5 water molecules, DMPS 3.8 water molecules and DMPC 3.5 water mol ecules. In the presence of cholesterol the number of water molecules b ound increases in the region where phase separation of cholesterol tak es place [D. Bach, Chem. Phys. Lipids 35 (1984) 385-392: E.J. Wachtel. N. Borochov, D. Bach, Biochim. Biophys. Acta 1066 (1991) 63-69: D. Ba ch, N. Borochov, E. Wacktel, Chem. Phys. Lipids, submitted]. (C) 1998 Elsevier Science B.V.