Zeaxanthin (dihydroxy-β-carotene) but not β-carotene rigidifies lipid membranes: a 1H-NMR study of carotenoid-egg phosphatidylcholine liposomes

Abstract

1H-NMR technique was applied to study liposomes formed with egg-yolk phosphatidylcholine containing as an additional component two carotenoid pigments: β-carotene or zeaxanthin (dihydroxy-β-carotene). A strong rigidifying effect of zeaxanthin but not of β-carotene with respect to hydrophobic core of lipid bilayer was concluded from the carotenoid-dependent broadening of the NMR lines assigned to -CH 2- groups and terminal -CH 3 groups of lipid alkyl chains. A similar effect of zeaxanthin with respect to polar headgroups was concluded on the basis of the effect of the pigment on the shape of NMR lines attributed to -N +(CH 3) 3 groups. In contrast, β-carotene increases motional freedom of lipid polar headgroups. The inclusion of both carotenoids to liposomes resulted in the enhanced penetration of Pr 3+ ions to the polar zone of the external layer of a membrane monitored by the splitting of the -N +(CH 3) 3 signal, the effect of β-carotene being much more pronounced. Differences in the effect on membrane structure and molecular dynamics observed for β-carotene and its polar derivative are discussed in terms of organization of a carotenoid-containing lipid membrane.