EN
Over the last decade we have investigated the effects of cholesterol, polar carotenoids, and integral proteins (peptides) on the structure, dynamics, and hydrophobicity of saturated and unsaturated phosphatidylcholine (PC) membranes. The major results obtained in our studies can be summarized as follows: (1) The effect of unsaturation on the membrane alkyl chain order and reorientational motion is negligibly small; (2) The translational diffusion of lipids (lateral or vertical) as well as the diffusion of lipid-soluble small molecules is significantly decreased in cis- and trans-unsaturated PC membranes; (3) cis-unsaturated alkyl chains greatly decrease the ordering effect of membrane modifiers (cholesterol, polar carotenoids) as well as their effect on alkyl chain reorientational motion; (4) Introduction of a double bond into the alkyl chain increases the hydrophobicity (decreases water penetration) at all locations in the membrane; (5) Incorporation of cholesterol (30 mol%) decreases hydrophobicity (increases water penetration) from the polar headgroup region to a depth of approximately C7 and C9 for saturated and unsaturated PC membranes, respectively. Membrane hydrophobicity sharply increases at these positions from the level of methanol to the level of pure hexane, and hydrophobicity is constant in the inner region of the membrane.