Interaction of isomeric forms of xanthophyll pigment zeaxanthin with dipalmitoylphosphatidylcholine studied in monomolecular layers.
Two-component monomolecular layers were formed with DPPC and two stereoisomers of zeaxanthin 9-cis and 13-cis at the argon-water interface. Very distinct over-additivity which represents affection of a lipid arrangement in the membrane has been observed in the case of zeaxanthin 9-cis (maximum at 20 mol%) but not in the case of zeaxanthin 13-cis. The differences in the organization of the isomers of zeaxanthin-DPPC monolayers are interpreted in terms of the different orientation of both xanthophylls at the interface observed at relatively high surface pressures (>25 mN/m) comparable to the surface pressures of biomembranes. The results are consistent with the model according to which zeaxanthin 9-cis adopts a vertical orientation at the polar-nonpolar interface in contrast to zeaxanthin 13-cis, which is oriented horizontally owing to the fact that it interacts by two hydroxyl groups with the same hydrophobic-hydrophilic interface in the monolayer. The findings are discussed in comparison with the behavior of zeaxanthin in the conformation all-trans in the same system. Zeaxanthin all-trans forms efficiently molecular aggregates in the mixed monolayers in contrast to cis isomers. Circular dichroism measurements show the formation of molecular structures by zeaxanthin 13-cis that are interpreted as dimers. FTIR measurements show that these dimers are stabilized by van der Waals interactions unlike aggregated structures formed by all-trans zeaxanthin that are stabilized by hydrogen bonding. Physiological importance of the differences in aggregation and orientation of stereoisomers of zeaxanthin in lipid environment is discussed.
Milanowska
Justyna
J
Department of Biophysics, Institute of Physics, Maria Curie-Sklodowska University, 20-031 Lublin, Poland.
Polit
Agnieszka
A
Wasylewski
Zygmunt
Z
Gruszecki
Wiesław I
WI
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry* / Q000493:pharmacokinetics; D008567:Membranes, Artificial; D013237:Stereoisomerism; D024341:Xanthophylls / Q000737:chemistry* / Q000493:pharmacokinetics; D065146:Zeaxanthins; D019207:beta Carotene / Q000031:analogs & derivatives / Q000737:chemistry* / Q000493:pharmacokinetics
D008567:Membranes, Artificial; D024341:Xanthophylls; D065146:Zeaxanthins; D019207:beta Carotene; D015060:1,2-Dipalmitoylphosphatidylcholine