NUCLEAR-MAGNETIC-RESONANCE INVESTIGATION OF HYDROCARBON CHAIN PACKINGIN BILAYERS OF POLYUNSATURATED PHOSPHOLIPIDS

H-2 nuclear magnetic resonance (NMR) on chain-deuterated phospholipids has been used to study the influence of the degree of unsaturation on lipid chain packing and on area per molecule at the lipid water inter face. Order and motions of deuterated stearic acid in position sn-1 of phosphatidylcholines (PC) containing 18:0, 18:1n-9, 18:2n-6, 18:3n-3, 20:4n-6, 20:5n-3, or 22:6n-3 in position sn-2 were investigated in pu re PC and in mixtures of PC in a phosphatidylethanolamine (PE) matrix. Results reveal that lipid packing in bilayers is mainly controlled by packing requirements at the lipid water interface. Increasing degrees of unsaturation lower chain order and increase area per PC molecule, whereas inclusion of PE in model membranes has the opposite effect. Ch ain order and motions in highly unsaturated lipid membranes are less s ensitive to changes in temperature. Temperature sensitivity decreases further upon incorporation of PC into a PE matrix. Unsaturation induce s chain disordering, which may be interpreted as an increase in area p er molecule of lipids toward the center of the bilayer. This may resul t in a lower packing density of unsaturated lipids at the lipid water interface. We hypothesize that these differences in lipid packing and dynamics may influence activity of membrane proteins.