THE HYDROPHOBIC ACYL-CHAIN EFFECT IN THE LIPID DOMAINS APPEARANCE THROUGH PHOSPHOLIPID-BILAYERS

An intermolecular interaction model for selective association processe s of double-chain phospholipids in bilayer lipid membranes has been pr oposed, analysed and solved numerically. A large variety of binary mix tures of asymmetrical double-chain phospholipids with the cross-sectio nal areas of the polar headgroups a(1) = 40 Angstrom(2) (the first com ponent) and a(2) = 60 Angstrom(2) (the second component) have been inv estigated. Changing the hydrophobic acyl-chain lengths of both mixture components, we found in all cases that the self-association probabili ty (the association of like-pairs of phospholipids) of the first compo nent in parallel alignment of the electric dipole moments of the polar headgroups is higher than the cross-association probability (the asso ciation of cross-pairs of phospholipids) and the self-association prob ability of the second component. This result is in good agreement with the experimental evidence that where the cross-sectional area of the polar headgroups matches the hydrocarbon chain-packing cross-sectional area (a congruent to 2 Sigma congruent to 40 Angstrom(2)), lipids pos sess a high tendency to aggregate into well packed bilayer structures with the acyl-chains oriented perpendicularly to the bilayer plane. Ou r theoretical data confirm that the double-chain phospholipids may ass ociate themselves into anti-parallel alignment of the polar headgroups (P22) as well. The hydrophobic acyl-chain effect of phospholipids may modulate the distribution of lipid domains within bilayers that have a large variety of functional roles in cellular metabolism. (C) 1998 E lsevier Science B.V. All rights reserved.